No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Organization of a Plant-Arthropod Association in Simple and Diverse Habitats: The Fauna of Collards (Brassica Oleracea)
Ecological Monographs
Abstract
Collards were grown at Ithaca, New York, in two experimental habitats: pure stands and single rows that were bounded on each side by diverse, meadow vegetation. The arthropods associated with these plants were sampled on 20 dates over a 3-year period. The status of the herbivore species was measured by their rank in biomass in each sample. The two most prominent species, Phyllotreta cruciferae and Pieris rapae, maintained high status throughout the investigation, but another important species, Brevicoryne brassicae, was absent for an entire season. Pit feeders usually formed the most important herbivore guild. Nevertheless, the guild spectrum, which describes the functional structure of the fauna, varied widely in time and space. The size distributions of species and of individuals were both highly skewed toward the smaller sizes. Herbivore loads, the mean biomass of herbivores per 100 g of consumable foliage, were consistently higher in the pure stands. Moreover, herbivore loads varied significantly with season in each experimental habitat. Both the number of herbivore species and the diversity of the herbivore load were greater in the diverse habitat. Biomass was more heavily concentrated among the prominent herbivores in the pure stands; increased dominance, rather than differences in species richness, appeared to be the major cause for the lower herbivore diversity in this habitat. The diversity of predators and parasitoids was higher in the pure stands. Most of the abundant species found on collards shared a similar narrow range of hosts. As a result the species in this core group of herbivores and parasitoids were regularly associated with each other. Predators and the less abundant herbivores tended to be less specialized and served to link the collard association with the surrounding community. Plant-arthropod associations are representative of component communities, well-integrated systems that form portions of larger compound communities. This distinction facilitates the analysis of community structure. Microclimates and the effectiveness of @'enemies@' did not appear to differ sufficiently in the two experimental habitats to account for the observed differences in the herbivore load. The results suggest a new proposition, the resource concentration hypothesis, which states that herbivores are more likely to find and remain on hosts that are growing in dense or nearly pure stands; that the most specialized species frequently attain higher relative densities in simple environments; and that, as a result, biomass tends to become concentrated in a few species, causing a decrease in the diversity of herbivores in pure stands.
... Further, diversifying crops favours the presence of non-host plants that dilute host species and create barriers between them (Andow 1991), leading to a lowered colonization and spread of insect pests (Mansion-Vaquié et al. 2020). Known as the 'resource concentration' hypothesis, this bottom-up effect of intercropping can be complemented by the 'enemies' hypothesis, i.e. the increase of biological control through the multiplication of ecological niches, the diversification of resources, and the reduction of inter-and intra-specific competition in complex agro-ecosystems (Root 1973). Evidence however shows that intercropping does not consistently provide benefits to natural enemies (Lopes et al. 2016;Rakotomalala et al. 2023). ...
... Aphids were significantly reduced in intercropping compared to sole cropping. It is consistent with previous findings (Lopes et al. 2016) and follows the 'resource concentration' hypothesis (Root 1973). Aphids are known to be sensitive to the physical and chemical camouflage of their host plants and barrier effects (Ninkovic et al. 2013;Döring 2014;Mansion-Vaquié et al. 2020) that are key 'associational resistance' mechanisms (sensu Tahvanainen and Root 1972) characterizing intercropping systems. ...
... Yet, wildflower strips further reduced aphid colonization in breadseed poppy-barley intercropping and enhanced predation in faba bean-wheat intercropping. In its seminal work proposing the 'enemies' hypothesis, Root (1973) highlighted the key role of non-crop flowers to support natural enemies in complex agro-ecosystems. While, modern intercropping systems tended to reduce the complexity to the sole diversity of crops (Brooker et al. 2015), the present results indicate that diversifying both the crop field and its margins can partially strengthen pest regulation. ...
Different diversification practices have the potential to reduce pests and therefore pesticide use. Yet, their integration at the agroecosystem level and the evaluation of their multifunctional effects remain limited. Through a two-year field experiment conducted in Germany, we tested whether associating intercropping (faba bean-wheat, followed by breadseed poppy-barley) with pluriannual wildflower strips strengthens the biological regulation of aphid pests and weeds, and enhances cropping system productivity. The contribution of flowering weeds to conservation biological control was also analysed. Aphid but also predator colonization and predation rates on bean and poppy were consistently lower in intercropping compared to sole cropping. Wildflower strips enhanced aphid predation in bean-wheat intercropping, and further reduced aphid colonization at 10 m distance but not at 20 m in poppy-barley intercropping. Weed biomass was consistently reduced in intercropping compared to sole cropping bean and poppy, and did not significantly affect bean and poppy yields in intercropping. The cover of one flowering weed species, Matricaria recutita, was negatively correlated to aphid colonization and positively correlated to predation rate. Matricaria recutita flowers were also visited more often by predatory hoverflies in plots adjacent to wildflower strips. Finally, land equivalent ratio was consistently higher than 1, and the highest in bean-wheat intercropping associated to wildflower strips. The study demonstrates the benefits of associating wildflower strips to intercropping to strengthen biological control and cropping system productivity. Flowering weeds, maintained at an acceptable level through intercropping, turn out to be relevant functional biodiversity in interacting with wildflower strips for conservation biological control.
... For example, Gagic et al. (2021) found that larger cotton fields located in landscapes with <10% semi-natural habitat experienced the earliest immigration and highest abundances of small, piercing-sucking arthropod pests. Once in a field, areas of high crop density can be more vulnerable to herbivory as specialist herbivores concentrate on that preferred resource at the local scale (a.k.a Resource Concentration Hypothesis; Root, 1973;Feeny, 1976). On the other hand, resource dilution effects can occur when high local crop density outstrips the ability of an herbivore population to take advantage of that resource, as seen in the declines of pollen beetles with increasing densities of oil rape seed plants (a.k.a Resource Dilution Hypothesis; Schneider et al., 2015). ...
... In contrast to herbivores, natural enemy groups often require alternative plant and prey resources to persist within agricultural fields. These alternative plant resources are important to consider in land management given that natural enemies can often control overall herbivory through predation of herbivores (Root, 1973;Landis et al., 2000;Wilby and Thomas, 2002). Specifically, increases in the density of crop plants at the local and landscape scales often decreases the availability of alternative plant resources, supporting fewer, less diverse natural enemies (Dassou and Tixier, 2016;Beaumelle et al., 2021). ...
... Finally, intrinsic biological factors such as diet breadth, specifically degree of diet specialization, could be a key functional trait modulating the effect of resource availability (Moreira et al., 2016) for both herbivores and natural enemies (Root 1973). Specialist herbivores are expected to be most sensitive to temporal changes in resource concentration as their development and reproduction is dependent upon a narrow range of host plants (Doublet et al., 2019). ...
Herbivory is a major fitness pressure for plants and a key driver of crop losses in agroecosystems. Dense monocultures are expected to favor specialist herbivorous insects, particularly those who primarily consume crop species; yet, levels and types of herbivory are not uniform within regional cropping systems. It is essential to determine which local and regional ecological factors drive variation in herbivory in order to support functional agroecosystems that rely less on chemical inputs. Crops in the genus Cucurbita host a suite of both generalist and specialist herbivores that inflict significant damage, yet little is known about the relative contribution of these herbivores to variation in herbivory and how local- and landscape-scale Cucurbita resource concentrations, management practices, and natural enemies mediate this relationship. In this study, we tested whether three foundational ecological hypotheses influenced Cucurbita herbivory across 20 pumpkin fields in the semi-arid Southern High Plains Region of Texas. We used generalized linear mixed models and confirmatory path analysis to assess whether the Density-dependent Herbivory Hypothesis, Resource Concentration Hypothesis, or the Natural Enemies Hypothesis, could explain variation in Cucurbita herbivory and insect dynamics in the context of conventional agronomic practices. We found that herbivory increased over time, indicating that herbivores were causing sustained damage throughout the growing season. We also found that fields with higher local Cucurbita resources had lower herbivory, suggesting a resource dilution effect. Natural enemy communities were more abundant and taxonomically rich in sites with greater generalist herbivore abundance, though predator abundance declined over time, indicating that late-season crop fields are most at risk given high herbivory and low natural enemy-based control. Our findings also suggest that while local resource availability may drive the abundance and richness of arthropod communities, additional agronomic and phenological information is needed to anticipate herbivory risk in an agriculturally dominated landscape.
... Top down control: Here, natural bio-agents (third trophic level) inhibit herbivores (second trophic level), and this sort of strategy is shown in "Augmentative biological control." Pest suppression as a result of this phenomenon, according to Root (1973), supports the "enemy" hypothesis. ...
... This strategy is used in "Conservation biological control" as habitat alteration. Root (1973) used the phrase "resource concentration hypothesis" to describe pest suppression caused by non-natural enemy impacts, implying that the resource (crop) was successfully "diluted" by signals from other plant species. ...
... When planted in a monoculture rather than a mixed crop, pests have an easier job locating host plants. This is based on the "Resource Concentration Hypothesis," which states that plant-feeding insects are more likely to identify and stay in patches of their host plants that are dense and less diversified (Root, 1973 (Staver et al., 2001). Marigold increases longevity and fecundity of natural enemies by providing nectar and pollen (Baggen et al., 1999). ...
Ecological engineering has recently emerged as a paradigm for considering pest
management approaches that rely on the use of cultural techniques to manipulate
farm habitat and to enhance biological control. In contrast to the intensive use
of ecosystems, these days to enhance productivity can affect agro-ecosystems
through soil and water depletion, biodiversity loss, challenging pest problems
and disruption in flow of ecosystem services. Ecological engineering for pest
management mainly focuses on increasing the abundance, diversity and function
of natural enemies in horticultural crops habitats by providing refuges and alternate
or supplementary food resources and also attracts different kinds of pollinators
like honeybees. The aim of ecological engineering in horticulture ecosystem is
to integrate soil and pest management strategies with regular practices of farmers
for the benefit of environment and farming community. It involves knowledge
of horticulture, ecology and farm economics, for restoration and construction of
healthy and sustainable horticulture ecosystems. By redesigning the horticulture
ecosystem, farmers can enhance biodiversity on their farms through adopting
polyculture, cover crops, corridors, crop rotations and various habitats. This is a
key strategy in sustainable horticulture to enhance biodiversity at the landscape
and field level. For example, the planting of buckwheat, Fagopyrum esculentum
as a cover crop in vineyards and alyssum, Lobularia maritima between rows of
vegetables provide resources for predators and parasitoids resulting in reduced
herbivore damage. The main approach in ecologically-based pest management 1s to
increase agro-ecosystem diversity and complexity as a foundation for establishing
beneficial interactions that keep pest populations in control.
... The effects of plant genotypic diversity on herbivore abundance may occur through additive (i.e., the sum of average effects of genotypes) or non-additive mechanisms (i.e., synergistic or antagonistic effects of multiple genotypes) (Schweitzer et al. 2005;Hughes et al. 2008;Utsumi et al. 2011;Hambäck et al. 2014). Additive effects (e.g., the resource concentration [RC] hypothesis) occur when plant genotypes experience the same herbivore abundance in single-genotype as in mixed-genotype plots (Root 1973); thus, the responses of herbivore abundance in mixed-genotype plots can be predicted based on those observed in single-genotype plots. The RC hypothesis supports this mechanism and predicts that mixed-genotype plots should be diluted in terms of the abundance of preferred genotypes for specialist herbivores. ...
... The RC hypothesis supports this mechanism and predicts that mixed-genotype plots should be diluted in terms of the abundance of preferred genotypes for specialist herbivores. In contrast, generalists are less sensitive to such dilution effects (Root 1973). Conversely, non-additive effects occur when the responses in diverse plant communities cannot be predicted from those in the single-genotype plots. ...
... The effects of plant genotypic diversity on specialist herbivore abundance may be additive or non-additive (Schweitzer et al. 2005;Hughes et al. 2008;Utsumi et al. 2011;Hambäck et al. 2014). The RC hypothesis predicts additive effects, in which dilution alone is sufficient to decrease the abundance of specialist herbivores in mixed-genotype plots compared with single-genotype plots (Root 1973). Thus, the responses of herbivore abundance in mixed-genotype plots can be predicted based on those observed in single-genotype plots. ...
Key message
The response of herbivore abundance to birch genotypic diversity varies depending on the host specificity of the herbivores. Specialist, but not generalist, herbivores were affected by birch genotypic diversity.
Abstract
Biological control is an important ecosystem service mediated through plant diversity. Responses of herbivore abundance to plant genotypic diversity may depend on host specificity, especially the host-feeding type. We conducted a common-garden experiment by manipulating plot-level genotypic diversity (number of source populations per plot) of Erman’s birch (Betula ermanii) to understand how birch genotypic diversity affected the abundance of three herbivore feeding types (chewers, galls, and suckers). Specifically, we investigated whether the effects of plant genotypic diversity on herbivore abundance were additive or non-additive. Furthermore, we examined this mechanism as a possible change in plant phenotype (plant productivity and/or leaf traits) and/or herbivore foraging behavior (associational resistance with neighboring plant individuals). We found that genotypic diversity had a significant positive effect on condensed tannin concentration; however, it did not affect plant growth. There was no effect of increasing birch genotypic diversity on the density of chewers (generalists) and chewing herbivory, whereas the density of galls and suckers (specialists) decreased significantly. A negative non-additive effect was observed with regard to gall density and a negative additive effect on sucker density was observed. Gall density was not related to the increase in condensed tannins affected by birch genotypic diversity. This implies that associational resistance is more likely to explain the negative non-additive effects on gall density. Our study shows that the loss of birch genotypic diversity due to shrinking population sizes will strongly affect specialist herbivores in the boreal forests of Hokkaido.
... predators and parasitoids; Albert et al., 2022;Jactel et al., 2020;Moreira et al., 2016;Schuldt et al., 2018Schuldt et al., , 2019. The influential "Enemies Hypothesis" (Root, 1973) posits that plant diversity promotes the diversity and abundance of natural enemies via increased habitat complexity, greater niche availability, and higher prey diversity (Langellotto & Denno, 2004;Moreira et al., 2016), which often results in enhanced top-down pressure on herbivores (Haddad et al., 2009;Jactel et al., 2020;Letourneau et al., 2011;Wan et al., 2020). In the case of forests, several recent studies provide evidence for the positive effects of tree diversity on the abundance and diversity of natural enemies (Ampoorter et al., 2020;Butz et al., 2023;Li et al., 2023;May-Uc et al., 2020;Nell et al., 2018;Penone et al., 2019;Stemmelen et al., 2022), but experimental tests involving assessments of predation pressure are still limited. ...
... Notably, marked functional differences between birds and arthropods, including different foraging behaviours, could shape their responses to tree diversity. For instance, natural enemy diet breadth has been proposed as an important factor modulating plant diversity effects on top-down herbivore control (Root, 1973). In this context, generalist natural enemies are expected to benefit more than specialist ones from the greater resource availability and diversity found in more speciesrich forest patches and thus show stronger responses to tree diversity (Bellone et al., 2020;Legault & James, 2018;Staab & Schuldt, 2020;Zhang et al., 2017). ...
... Enemies Hypothesis (Root, 1973) and suggests that tree diversity strengthens top-down control of insect herbivores by insectivorous birds in forests. Importantly, the top-down control of herbivores by birds may be more pronounced in older, natural forests, given that bird predation positively covaried with stand age. ...
Tree diversity can promote both predator abundance and diversity. However, whether this translates into increased predation and top‐down control of herbivores across predator taxonomic groups and contrasting environmental conditions remains unresolved. We used a global network of tree diversity experiments (TreeDivNet) spread across three continents and three biomes to test the effects of tree species richness on predation across varying climatic conditions of temperature and precipitation. We recorded bird and arthropod predation attempts on plasticine caterpillars in monocultures and tree species mixtures. Both tree species richness and temperature increased predation by birds but not by arthropods. Furthermore, the effects of tree species richness on predation were consistent across the studied climatic gradient. Our findings provide evidence that tree diversity strengthens top‐down control of insect herbivores by birds, underscoring the need to implement conservation strategies that safeguard tree diversity to sustain ecosystem services provided by natural enemies in forests.
... Diversified systems create conditions less favorable for pest arthropods and more conducive for natural enemies (Gómez-Marco et al. 2016;Meyling et al. 2013;Piñero and Manandhar 2015;Ponti et al. 2007). Secondary plants can serve as physical barriers, offer visual and olfactory camouflage, and act as repellents against pests (Finch and Collier 2000;Parolin et al. 2012;Piñero and Manandhar 2015;Root 1973). In addition, they can attract natural enemies, support their establishment in crop fields, provide refugia, and offer food resources, enhancing biological control (Landis et al. 2000;Root 1973;Sheehan 1986). ...
... Secondary plants can serve as physical barriers, offer visual and olfactory camouflage, and act as repellents against pests (Finch and Collier 2000;Parolin et al. 2012;Piñero and Manandhar 2015;Root 1973). In addition, they can attract natural enemies, support their establishment in crop fields, provide refugia, and offer food resources, enhancing biological control (Landis et al. 2000;Root 1973;Sheehan 1986). The success of using secondary plants for pest control varies widely among studies in different countries, influenced by the target pest, plant species, experimental design, and climatic conditions (Hahn and Cammarano 2023). ...
... The natural enemies hypothesis explains the suppression of aphids in Brassica crops intercropped with Poaceae or flowering plants (Root 1973;Vidal 1997), suggesting that such secondary plants enhance biological control. In a review of the effects of secondary plants on pest control, Piñero and Manandhar (2015) reported that in most studies, reductions of aphids or aphid-transmitted viruses were associated with an increase in aphidophagous hoverflies, subfamily Syrphinae (Diptera: Syrphidae). ...
Diversifying crop habitats and controlling arthropod pests by cultivating “secondary plants” alongside a primary crop is a frequently discussed strategy. The effectiveness of using secondary plants to manage pests varies across countries, and is influenced by factors such as the target pest, plant species, experimental design, and climatic conditions. Consequently, we conducted a study investing the impact of intercropping wheat or barley with additional flower strips on controlling aphid pests in white cabbage fields in Japan and Germany.Query Our results in Japan supported the natural enemies hypothesis, leading to a significant reduction in populations of two pest aphids: the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), and the cabbage aphid, Brevicoryne brassicae (L.) (Hemiptera: Aphididae). Furthermore, intercropping and/or flower strips increased the proportions of natural enemies, including hoverfly larvae (Diptera: Syrphidae), ladybirds (Coccinellidae: Coleoptera), and parasitoid wasps (Hymenoptera: Braconidae), relative to the aphids. Hoverfly larvae, due to their high abundance, appeared to be Japan’s most effective aphid suppressors. In contrast, in Germany, intercropping and flower strips did not remarkably suppress aphid populations or enhance the presence of the natural enemies, despite a temporary increase in the population density of hoverfly larvae in intercropping. These disparities between the trials in the two countries may be attributed to variations in regional and local biodiversity. This suggests that using secondary plants for pest control should consider the specificities of local environments.
... Till now, the associational resistance hypothesis has been recognized as the primary mechanism driving the dilution effect of increased plant diversity on specialist herbivory (Root, 1973;Agrawal et al., 2006;Lewinsohn and Roslin, 2008). This hypothesis claims that specialist herbivores prefer homogeneous neighbors to the same host plants for increase their herbivore loads (Lewinsohn and Roslin, 2008). ...
... This result suggests that mixed plantation of phylogenetically distant plant species can have a clear dilution effect on herbivory intensity from specialist pest. This pattern can be explained by the associational resistance hypothesis, which claims that specialist herbivores prefer more homogeneous neighbors to their preferred host plants to increase their loads (Root, 1973;Agrawal et al., 2006;Lewinsohn and Roslin, 2008). Thus, increasing the numbers of phylogenetically distant tree species will dilute specialist herbivores, thereby decreasing the abundance of specialist herbivores (Tahvanainen and Root, 1972;Barbosa et al., 2009). ...
Pest herbivory regulation is one of the key functions provided by diverse ecosystems, especially when compared to species depauperate agro-ecosystems and in the context of increased pest outbreaks due to global change. The dilution effect of host diversity on insect herbivory suggests that mixed plantations are feasible for regulating pest herbivory in agroecosystems. Dilution effect of increased plant diversity on insect herbivory has been widely observed, yet little is known about how it may change with plant phylogenetic relatedness and herbivore specialization, especially at the community level. Here, we compared herbivore richness, abundance, and degree of herbivory (i.e., the ratio of trees damaged by pest and total trees in a given area) among the two monocultures and the four mixed plantations in Wenchang city, Hainan Province, China. We also respectively assessed the effects of phylogenetically close or distant species on generalist and specialist herbivores in monocultures and mixture. We found that increasing the number of phylogenetically closely-related tree species could dilute generalist herbivore richness, abundance, and degree of herbivory but amplify specialist herbivore richness, abundance, and degree of herbivory. In contrast, increasing the number of phylogenetically distant tree species increased generalist herbivore richness, abundance, and degree of herbivory, while reducing specialist herbivore richness, abundance, and degree of herbivory. Our results suggest that plant phylogenetic relatedness and herbivore specialization can indeed interact to influence pest control efficiency when using mixed plantations to manage pest herbivory in agroecosystems. Thus, both herbivore specialization and plant phylogenetic relatedness should be taken into account in the management of agro-ecosystems and biodiversity conservation with respect to herbivory.
... In two excellent review papers, much information about plant defense theories is given. In 1992, Herms and Mattson published their review paper on evolutionary theories of plant defense, focusing on plant physiological trade-offs interacting with the abiotic environment, competition and herbivory (Root 1973). The plant apparency theory distinguishes between plants that are relatively "hard to find", as small, ephemeral, early succession plant species, and those who are "bound to be found", as huge, late succession tree species. ...
... The plant apparency theory distinguishes between plants that are relatively "hard to find", as small, ephemeral, early succession plant species, and those who are "bound to be found", as huge, late succession tree species. Plants in the first category rely on 'escape in time and space' from their adapted enemies, plants in the second category are predicted to be more defended (Root 1973, Feeny 1976, see Castagneyrol et al. 2013 for a field study on tree apparency). Bilberry is a plant species that belongs to the second category and is therefore, at least according to these two plant defense theories, predicted to be defended against herbivores. ...
Bilberry responses to herbivory: phenolic concentrations and subsequent insect herbivory. Marcel Schrijvers-Gonlag, PhD thesis. Submitted 8 January 2024. Not approved by the Evaluation Committee. The first two papers have been published, the third paper is only available as manuscript in this thesis. At the end of my thesis, I added the Assessment from the Evaluation Committee which may be useful for fellow PhD students.
... This is consistent with the resource heterogeneity hypothesis (Hutchinson, 1959;Lewinsohn & Roslin, 2008;Moreira et al., 2016), as a greater diversity of herbivores provides more specialized prey for certain carnivores, leading to an increase in their richness. Additionally, diverse plant communities can provide more structurally diverse habitats (Strong, 1984), which can support higher abundances of predators and limit herbivore populations (the Enemies Hypothesis, Root, 1973). While many manipulating biodiversity experiments have found a positive correlation between plant diversity and consumer diversity (herbivores and carnivores) (Koricheva et al., 2000;Haddad et al., 2001;Wimp et al., 2004;Crutsinger et al., 2006;Johnson et al., 2006;Haddad et al., 2009;Scherber et al., 2010;Borer et al., 2012;Ebeling et al., 2018), there have been a few observational and experimental studies that reported no impact of plant diversity on consumer diversity (Currie, 1991;Wright & Samways, 1998;Hawkins & Porter, 2003;Jetz et al., 2009). ...
... The observed impact of treatment may not be a result of indirect plant diversity loss, as herbivore richness was not related to plant diversity ( Figures 6A, 7A). Instead, this may correspond to the resource concentration hypothesis (Root, 1973), which suggests that specialist herbivores are attracted to their host plants when other forbs are removed, leading to an increase in herbivore richness. This hypothesis is based on the idea that high plant diversity will increase nutrient heterogeneity within the plant community, and highquality resources will be diluted, leading to a reduction in arthropod diversity (Otway et al., 2005). ...
Plant species loss, driven by global changes and human activities, can have cascading effects on other trophic levels, such as arthropods, and alter the multitrophic structure of ecosystems. While the relationship between plant diversity and arthropod communities has been well-documented, few studies have explored the effects of species composition variation or plant functional groups. In this study, we conducted a long-term plant removal experiment to investigate the impact of plant functional group loss (specifically targeting tall grasses and sedges, as well as tall or short forbs) on arthropod diversity and their functional groups. Our findings revealed that the removal of plant functional groups resulted in increased arthropod richness, abundance and the exponential of Shannon entropy, contrary to the commonly observed positive correlation between plant diversity and consumer diversity. Furthermore, the removal of different plant groups had varying impacts on arthropod trophic levels. The removal of forbs had a more pronounced impact on herbivores compared to graminoids, but this impact did not consistently cascade to higher-trophic arthropods. Notably, the removal of short forbs had a more significant impact on predators, as evidenced by the increased richness, abundance, the exponential of Shannon entropy, inverse Simpson index and inverse Berger-Parker index of carnivores and abundance of omnivores, likely attributable to distinct underlying mechanisms. Our results highlight the importance of plant species identity in shaping arthropod communities in alpine grasslands. This study emphasizes the crucial role of high plant species diversity in controlling arthropods in natural grasslands, particularly in the context of plant diversity loss caused by global changes and human activities.
... Plant diversity effects on species interactions and ecosystem function have been widely documented (Tilman et al. 2001;Cardinale et al. 2011;Hooper et al. 2005). Within this body of work, the "Enemies Hypothesis" poses that plant diversity promotes the abundance and diversity of natural enemies (i.e., predators and parasitoids), ultimately favouring topdown control of herbivores (Root 1973;Haddad et al. 2009;Letourneau et al. 2011). In the case of forests, however, a recent meta-analysis by Stemmelen et al. (2022) found support for predicted increases in natural enemy abundance and diversity with tree diversity but no overall effect of tree diversity on predation pressure. ...
... In line with a previous study in this system by Nell et al. (2018), we observed higher attack rates by birds on clay caterpillars in tree polycultures relative to monocultures for two surveys, one in winter (December 2018) and another in late summer (October 2020). These results align with the Enemies Hypothesis, suggesting that plant diversity enhances predation pressure (Root 1973). However, they also indicate that these effects are not universal but rather dynamic and context-dependent. ...
Tree diversity promotes predator abundance and diversity, but evidence linking these effects to increased predation pressure on herbivores remains limited. In addition, tree diversity effects on predators can vary temporally as a function of environmental variation, or due to contrasting responses by different predator types. In a multi-year study, we assessed temporal variation in tree diversity effects on bird community abundance, diversity, and predation rates as a whole and by functional group based on feeding guild (omnivores vs. insectivores) and migratory status (migrant vs. resident). To this end, we conducted bird point counts in tree monocultures and polycultures and assessed attacks on clay caterpillars four times over a 2-year period in a tree diversity experiment in Yucatan, Mexico. Tree diversity effects on the bird community varied across surveys, with positive effects on bird abundance and diversity in most but not all surveys. Tree diversity had stronger and more consistent effects on omnivorous and resident birds than on insectivorous and migratory species. Tree diversity effects on attack rates also varied temporally but patterns did not align with variation in bird abundance or diversity. Thus, while we found support for predicted increases in bird abundance, diversity, and predation pressure with tree diversity, these responses exhibited substantial variation over time and the former two were uncoupled from patterns of predation pressure, as well as contingent on bird functional traits. These results underscore the need for long-term studies measuring responses by different predator functional groups to better understand tree diversity effects on top-down control.
... Preserved environments with high biodiversity tend to have a high richness of herbivorous insects (Root 1973, Fleck & Fonseca 2007. Among the different types of herbivory observed in these environments, the endo-phytophagous habit is considered one of the most threatened by environmental changes, including gallinducing insects, which are considered the most sophisticated on planet Earth (Shorthouse et al. 2005), as they can induce structures called galls through disordered processes of hyperplasia and/or hypertrophy and cell differentiation in different organs of host plants (Mani 1964, Oliveira & Isaias 2010, Ferreira & Isaias 2013. ...
... These will further increase vulnerability at 255 community level. According to the enemies hypothesis (Root 1973), which posits a positive 256 effects of plant richness on natural enemies, the higher trophic levels in our study (e.g. 257 predators and parasitoids) would benefit from tree diversity and regulate herbivores thereby 258 (Staab and Schuldt 2020). ...
Environmental factors can influence ecological networks, but these effects are poorly understood in the realm of the phylogeny of host-parasitoid interactions. Especially, we lack a comprehensive understanding of the ways that biotic factors, including plant diversity, tree identity, genetic diversity, overall community composition of higher trophic levels, and abiotic factors such as microclimate, interact to determine host–parasitoid network structure and host–parasitoid community dynamics. To address this, we leveraged a five-year dataset of trap-nesting bees and wasps and their parasitoids collected in a highly-controlled, large-scale subtropical tree biodiversity experiment. We tested for effects of tree species richness, tree phylogenetic and functional diversity, and taxonomic and phylogenetic composition on taxonomic, phylogenetic, and network composition of both host and parasitoid communities. We show that multiple components of tree diversity, tree composition, and canopy cover impacted both, taxonomic and phylogenetic composition of hosts and parasitoids. Generally, top-down control was stronger than bottom-up control via phylogenetic association between hosts and parasitoids, reflecting non-randomly structured interactions between phylogenetic trees of hosts and parasitoids. Further, host-parasitoid network structure was influenced by tree species richness, tree phylogenetic diversity, and canopy cover. Our study indicates that the composition of higher trophic levels and corresponding interaction networks are determined by habitat structure and heterogeneity, which is maintained by trees and especially via phylogenetic links in species-rich ecosystems.
... It is suggested that the impacts of natural enemies, i.e. predators and parasitoids, on outbreaking insects will be greater in more diverse habitats, especially those with more plant species, since this would promote higher natural enemy abundance and diversity (Andow 1991;Russell 1989;Root 1973). It is generally accepted that more diverse habitats provide greater diversity of predator species and microhabitats for generalist natural enemies and a greater diversity of resources for adult parasitoids. ...
This thesis aims to investigate different trophic interactions related to the outbreaking cycles of the forest tent caterpillar (Malacosoma disstria Hübner, Lepidopter:Lasiocampidae), both top-down and bottom-up, in the two types of forests, the boreal and the temperate. Throughout field studies, we determined that forest tent caterpillar early-instar larvae were more susceptible to mortality due to pathogens and maternal effects in years after the outbreak than to predators. These results suggest delayed density dependence and contribute to low endemic levels between outbreak peaks. We also investigated the overwintering mortality of forest tent caterpillars at the egg stage. While larger egg masses tended to promote survival, this factor was not the only significant predictor. Mortality was also related to average winter temperature variation and cold spells. With increasingly unpredictable
climate patterns, both factors could cause high mortality levels during the winter. Finally, with the high amount of organic material released during the outbreaks, we investigated the impact on potential predators, such as ants. We observed a shift in ant communities in the boreal forest but not in temperate forests, suggesting that disturbances caused by the forest tent caterpillar can alter less ecologically complex and redundant ecosystems. Forest tent caterpillars are important disturbance agents and participate in multiple trophic interactions during outbreaks, cementing the importance of a better understanding of their population dynamics.
... Intraplot diversification may lead to the emergence of foliar disease regulation processes that do not occur under monospecific cover [83,84]. The resource concentration hypothesis [85] reflects the fact that mixing multiple host and non-host plant species results in the 'dilution' of susceptible individuals within the plant cover, thereby limiting the development of the pathogen population. Increasing the proportion of non-host plants in a mixture reinforces this effect [83]. ...
Diversification at the plot level, through the use of intercropping (mixtures of crops), is an alternative to the conventional system of intensive agriculture, based on monospecific, usually single-variety canopies. Intercropping has been shown to provide benefits in terms of disease control. However, competition phenomena and the heterogeneity of the associated crops raise new ecological questions, particularly with regard to the dynamics and evolution of parasite populations. No study has assessed the potential impact of these associations on the dynamics of pathogenic species complexes. Changes in the nutritional status of plants and therefore in their physiological susceptibility to infection within intercropping systems could contribute to an increased diversity of ecological niches and thus affect the composition of the parasitic complex and its spatiotemporal dynamics. In this review, focusing on foliar diseases of fungal origin, and after outlining some elements of the biology and epidemiology of these fungal diseases, we will (i) describe the mechanisms that contribute to the composition of disease clusters and that drive interactions, but we will also review the strategies that these foliar diseases have adopted to deal with these co-infections; (ii) define how intercropping can lead to changes in epidemic dynamics, in particular by presenting the mechanisms that have a direct and indirect effect on disease evolution; and (iii) present the approach that should be adopted to properly study intercropping correctly in a multi-infection situation.
... Vegetation may play an important role in predator-prey interactions in this case (Li et al., 2018), and our findings would support the enemies' hypothesis. According to this hypothesis, plant species diversity is positively related to the abundance of predatory arthropods (Root, 1973;Russell, 1989). Our study demonstrates that the abundance of the predator guild increased positively as plant diversity/vegetation heterogeneity increased. ...
... Além disso, a policultura permite a presença de maior diversidade de insetos herbívoros, que podem funcionar como fontes alternativas de alimento para os inimigos naturais e, fazê-los permanecer no campo, nas épocas em que a população da praga principal está baixa (ROOT, 1973;ALTIERI, 1989;VANDERMEER, 1990;ANDOW, 1991). ...
In: AQUINO, A. M.; ASSIS, R. L. (Ed.). Agroecologia: princípios e técnicas para uma agricultura orgânica sustentável. Brasília, DF: Embrapa Informação Tecnológica, 2005. p. 325-339.
... This finding supports the disruptive crop hypothesis, which suggests that herbivores in polycultures will have a harder time locating crop plants associated with one or more taxonomically or genetically different plants compared to those in [81,82]. Given that we did not measure the natural enemy population in this experiment to validate the natural enemy hypothesis [83], we recommend further research to evaluate the relationships between the richness and abundance of natural enemies and natural biological pest control in these agricultural systems. ...
Diversifying agroecosystems enhance the sustainability of agricultural production and reduce input dependency during agroecological transitions. To achieve this objective, a study was conducted to assess the impact of intercropping and the introduction of flowering plant strips on land use efficiency and crop damage in a lettuce and broccoli association. The results indicated that the introduction of flowering plant strips alone led to a significant increase in land use efficiency, while intercropping alone did not have any such effect. The efficiency was measured using the land use equivalent ratio (LER), which consistently showed values greater than 1, suggesting a significant increase in efficiency. It should be noted that the presence of flower strips in the crop fields were found to increase the incidence of molluscs and Plutella xyllostella. Additionally, the competitive ratio analysis revealed that broccoli was more competitive than lettuce in the intercropping system. Therefore, farmers can increase the efficiency of land use and profitability by incorporating flower strips in the intercropping systems of broccoli and lettuce.
... Moreover, the secondary dominance of mammals as caterpillar predators could be attributed to the higher population of small mammals like carnivorous mammals and rodents within an agroecosystem, which often predates on insect pests and undervalued ecosystem services by mammals (Williams et al. 2018). Our ndings conform to the 'Enemies hypothesis', which posits that the e cacy of top-down control by predators is expected to rise coupled with plant diversity and structure (i.e., increased tree cover) (Root 1973;Yang et al. 2018). This is attributed to the potential enhancement of diverse plant communities in fostering the diversity and stability of habitat niches and resources essential for supporting a heightened abundance and diversity of predators (Yang et al. 2018). ...
Prey-predator interactions are fundamental to ecosystems, with predators regulating prey populations. Yet, the degree of this interaction varies, depending on the conditions and structure of the ecosystem. We investigated the impact of urbanisation and tree cover, together with leaf herbivory, on the risk of predation of caterpillar prey. We used 1500 arti cial caterpillars across ten study sites in southcentral Mindanao, Philippines. We found that the predation rate was similar across leaf herbivory treatments, but the risk differed signi cantly according to the predator and landscape variables. Arthropods were the most signi cant predators, and local landscape and plot-level variables affected the overall predation risk of caterpillar prey. Increasing canopy and tree cover increased the risk of predation. This study implies that, irrespective of the speci c foraging locations chosen by arthropod prey, predators are likely to prey on the available prey within the environment. Our results align with the 'Enemies hypothesis', which suggests that the effectiveness of top-down control by predators increases with heightened tree cover. This further suggests that adjacent small-scale restoration interventions, such as native tree planting to bolster habitat heterogeneity and structure, would bene t top-down control (i.e. natural pest control) within urban agroecosystems.
... It was realized in the current study that their numbers increased because of the rising pest numbers. This is in accordance with the enemy hypothesis proposed by Root (1973), which states that there is likely to be variations in the number of aphid specialist predators like D. rapae, which are expected to accumulate in simpler habitats where their specific prey (aphids) achieved higher densities and are easier to find (Sheehan, 1986). According to this hypothesis, their numbers fell behind that of the aphids (K strategists). ...
... network perspectives that go much beyond logging bi-trophic interactions for individual pests or conservation priority targets (Dee et al., 2017;Ma et al., 2019;Wyckhuys et al., 2021;Allen et al., 2022). Indeed, by viewing the tri-trophic interactions between BCAs, lepidopteran hosts and host plants comprehensively, ecological concepts based on various hypothesis including natural enemy, resource concentration, insurance, and aggregation can be put into practice (Root, 1973 et al., 2021) and the imperatives of biodiversity conservation and onfarm pest resilience can be made mutually enforcing (Tscharntke et al., 2021;Wyckhuys et al., 2022). The examination of the strength of the reported interactions with the various biological theories (hypotheses) are also important to investigate the impact of species decline on FAW biological control practice. ...
Biodiversity loss, as driven by anthropogenic global change, imperils biosphere intactness and integrity.
Ecosystem services such as top-down regulation (or biological control; BC) are susceptible to loss of extinction-prone
taxa at upper trophic levels and secondary ‘support’ species e.g., herbivores. Here, drawing upon curated
open-access interaction data, we structurally analyze trophic networks centered on the fall armyworm Spodoptera
frugiperda (Lepidoptera: Noctuidae) and assess their robustness to species loss. Tri-partite networks link 80 BC
organisms (invertebrate or microbial), 512 lepidopteran hosts and 1194 plants (including 147 cultivated crops)
in the Neotropics. These comprise threatened herbaceous or woody plants and conservation flagships such as
saturniid moths. Treating all interaction partners functionally equivalent, random herbivore loss exerts a
respective 26 % or 108 % higher impact on top-down regulation in crop and non-crop settings than that of BC organisms (at 50 % loss). Equally, random loss of BC organisms affects herbivore regulation to a greater extent
(13.8 % at 50 % loss) than herbivore loss mediates their preservation (11.4 %). Yet, under moderate biodiversity
loss, (non-pest) herbivores prove highly susceptible to loss of BC organisms. Our topological approach spotlights
how agriculturally-subsidized BC agents benefit vegetation restoration, while non-pest herbivores uphold biological
control in on- and off-farm settings alike. Our work underlines how the on-farm usage of endemic biological
control organisms can advance conservation, restoration, and agricultural sustainability imperatives. We
discuss how integrative approaches and close interdisciplinary cooperation can spawn desirable outcomes for
science, policy and practice.
... In general, compensatory mechanisms associated with interspecific competition have been assumed to be demographic in nature, with abundance representing a useful metric for assessing the strength of competition as a structuring mechanism. Density compensation is based on the premise that a particular species will be more abundant if it experiences less interspecific competition (Root 1973;Hawkins and McMahon 1989). However, number of individuals may be a poor measure of the ecological or evolutionary responses of species, as not all species require the same per capita quantity of resources. ...
Interspecific competition, environmental filtering, or spatial variation in productivity can contribute to positive or negative spatial covariance in the abundances of species across ensembles (i.e., groups of interacting species defined by geography, resource use, and taxonomy). In contrast, density compensation should give rise to a negative relationship between ecomorphological similarity and abundance of species within ensembles. We evaluated (1) whether positive or negative covariances characterized the pairwise relationships of 21 species of Congolese shrew, and (2) whether density compensation characterized the structure of each of 36 Congolese shrew ensembles, and did so based on the abundances or biomasses of species. In general, positive covariance is more common than negative covariance based on considerations of abundance or biomass, suggesting dominant roles for environmental filtering and productivity. Nonetheless, negative covariance is more common for ecomorphologically similar species, suggesting a dominant role for competition within functional groups. Effects of abundance or biomass compensation, via pairwise or diffuse competitive interactions, were detected less often than expected by chance, suggesting that interspecific competition is not the dominant mechanism structuring these ensembles. Effects of competition may be balanced by responses to variation in resource abundance among sites in a landscape or among niche spaces within sites. Future studies of compensatory effects should incorporate considerations of heterogeneity in the abundance and distribution of resources in ecological space to better isolate the effects of competition and resource abundance, which can have opposing effects on community structure.
... Pest outbreaks are rare in polyculture condition due to the ability of the diverse plant culture to self-sustain through natural pest control by increasing the occurrence of natural enemies (Scherr and McNeely 2008). Polyculture offers alternate prey or hosts and alternate food sources such as pollen and nectar (Root 1973). Polycultures that support high densities of natural enemies might have increased incidence of predation and parasitization of herbivores (Altieri and Letourneau 1982). ...
Field experiment was carried out during 2014 to 2015 at Dryland Agricultural Research Station, Chettinad, Sivagangai district to find out cost-effective groundnut based intercropping system to enhance the activities of natural enemies viz spider and egg parasitoid. Groundnut (Arachis hypogaea Linnaeus; Variety: VRI II) when intercropped with bajra (Pennisetum glaucum L.; Variety: Co 7) 4:1 ratio attracted the highest population of natural enemies like spider and egg parasitoid, recording the population of 4.00 nos./10 plants and 10.56 per cent, followed by groundnut + sorghum (Sorghum bicolor L.; Variety: Co 30), maize (Zea mays L.; Variety; Co 6), groundnut + marigold (Tagetes erecta L.; Variety: MDU 1), groundnut + marigold (Tagetes erecta L.; Variety: MDU 1), groundnut + redgram (Cajanus cajan L.; Variety: VBN (Rg) 3) and groundnut + onion (Allium cepa L.; Variety: Co 1), while it was 2.39 nos./10 plants and 7.67 percent in groundnut pure crop.
... Pest outbreaks are rare in polyculture condition due to the ability of the diverse plant culture to selfsustain through natural pest control by increasing the occurrence of natural enemies (Scherr and McNeely, 2008). Polyculture offers alternate prey or hosts and alternate food sources such as pollen and nectar (Root, 1973). Polycultures that support high densities of natural enemies might have increased incidence of predation and parasitization of herbivores (Altieri and Letourneau, 1982). ...
... It is not clear what led to this underyielding, but it is possible that microbial decomposition could be inhibited by secondary plant metabolites leached by other litters (Srivastava et al., 2009). The alternative hypothesis, that litter diversity reduces the search efficiency of macroinvertebrates that have been evolved to select the most nutritious litter ("Resource concentration hypothesis": Root, 1973), has been shown to apply primarily to temperate latitudes with seasonal litterfall (Boyero et al., 2021). Further, in our study, most macroinvertebrates were mosquito larvae, which have minor effects on decomposition. ...
The effects of biodiversity on ecological processes have been experimentally evaluated mainly at the local scale under homogeneous conditions. To scale up experimentally based biodiversity‐functioning relationships, there is an urgent need to understand how such relationships are affected by the environmental heterogeneity that characterizes larger spatial scales. Here, we tested the effects of an 800‐m elevation gradient (a large‐scale environmental factor) and forest habitat (a fine‐scale factor) on litter diversity–decomposition relationships. To better understand local and landscape scale mechanisms, we partitioned net biodiversity effects into complementarity, selection, and insurance effects as applicable at each scale. We assembled different litter mixtures in aquatic microcosms that simulated natural tree holes, replicating mixtures across blocks nested within forest habitats (edge, interior) and elevations (low, mid, high). We found that net biodiversity and complementarity effects increased over the elevation gradient, with their strength modified by forest habitat and the identity of litter in mixtures. Complementarity effects at local and landscape scales were greatest for combinations of nutrient‐rich and nutrient‐poor litters, consistent with nutrient transfer mechanisms. By contrast, selection effects were consistently weak and negative at both scales. Selection effects at the landscape level were due mainly to nonrandom overyielding rather than spatial insurance effects. Our findings demonstrate that the mechanisms by which litter diversity affects decomposition are sensitive to environmental heterogeneity at multiple scales. This has implications for the scaling of biodiversity–ecosystem function relationships and suggests that future shifts in environmental conditions due to climate change or land use may impact the functioning of aquatic ecosystems.
... The 'enemies' hypothesis suggests that diversified environments favour natural enemies of pests because they contain: (i) more diverse populations of herbivores (i.e. prey and hosts); (ii) more microhabitats offering as many ecological niches; and (iii) more nectar and pollen sources (Root, 1973). Meta-analyses showed that increasing plant diversity at the field scale (notably through intercropping and companion planting) enhances the abundance of natural enemies in general (Letourneau et al., 2011), and predator abundance and diversity in particular (Dassou and Tixier, 2016). ...
In an attempt to restore functional biodiversity-delivering ecosystem services, several alternative agricultural approaches have emerged. Among these, two have been particularly acknowledged in recent decades: organic agriculture, with its aim to restrict the use of synthetic intrants, and conservation agriculture, promoting soil health via reduced soil tillage, permanent soil cover and crop diversification. Both approaches share the same overarching objective of restoring ecological functions and services to reach higher autonomy and resilience, yet, they have long represented two distinct communities. Today, interests from both parties are starting to converge: organic farmers are willing to provide more attention to their soils and conservation farmers are willing to decrease their dependency on synthetic intrants. However, when combining both approaches, farmers are left with no curative tools to combat pests and preventive agroecological practices become of the uttermost importance. This chapter reviews the challenge of controlling pests when opting for a combination of organic and conservation agriculture principles, reviewing the scientific knowledge on agroecological practices managing pests, then presenting the feedback of eight farmers in Belgium who have opted for this ambitious approach of organic-conservation agricultures combined.
... While, in the British flora, Umbellifera species (Lawton and Price 1979) and trees (Moran and Southwood 1982;Kennedy and Southwood 1984) with large leaf areas and less divided supported more diverse insect communities. The diversity of both insect guilds was positively affected by mean plant cover, as expected by the resource concentration hypothesis (Root 1973). Species providing most of the resources in our community (e.g. ...
Herbivorous insect assemblages are functionally diverse, with each species exploiting plant tissues in different ways. Availability and palatability of plant tissues influence the diversity and composition of herbivorous insect assemblages. However, few studies have compared herbivorous insect assemblages and their ecological correlates across multiple plant species within the same plant community. Here, we sampled insect assemblages from the canopies of 1060 plants belonging to 36 woody species in two mixed Mediterranean forest stands. 401 insect species were classified as herbivores and grouped into sucker or chewer guilds. We explored differences in the diversity and composition of each insect guild across plant species, and tested their relationships with plant leaf traits, abundance or phylogeny, and explored whether the structures of plant-herbivorous insect networks depended on any of the studied plant traits. Plant identity accounted for the highest proportion of variation in the composition of each insect guild. Plant species abundance showed a positive effect on both insect guilds’ diversity. Suckers’ diversity was higher in plant species with deciduous leaves and low SLA, while the composition was more similar between phylogenetically closer plant species. Chewers diversity increased with the leaf area, while plants with similar LA, leaf nitrogen, SLA and distinct leaf habit showed more similar assemblages. Similarly, closely related angiosperms showed similar chewer assemblages. Plant–insect interaction networks present a modular structure, in which plants belonging to the same module tend to be related and share more sucker species. We add to the evidence supporting the role of plant species features as filters for structuring their associated herbivore insect assemblages.
... Moreover, based on the "enemy hypothesis", the control of herbivores by their natural predators is predicted to be more effective in diversified crop environments compared to simplified ones. This is because natural predators may be more prevalent in habitats that provide a wider range of prey-host species and microhabitats for them to exploit [42]. ...
The main reason for adding plants to accompany the main crop is to protect it from pests and diseases. We reviewed the effectiveness of white mustard (Sinapis alba L.), sweet alyssum (Lobularia maritima L.), and coriander (Coriandrum sativum L.) in this regard. White mustard proximity had a strong positive influence on the occurrence of Syrphidae, parasitoids, Coccinellidae, and Carabidae, as well as on the fertility of Syrphidae and the longevity of parasitoids—all of which are essential for biological pest control. It also reduced many pests and diseases. The influence of S. alba on yield depends on the spacing used and the species of protected plant. Sweet alyssum positively affected the occurrence of Syrphidae, Coccinellidae, Anthocoridae, epigeal, and soil fauna, as well as the longevity of parasitoids and Anthocoridae. Its effect on the crop yield is variable, depending on the references consulted. The sensitivity of L. maritima to Phyllotreta spp. excludes it as a companion plant for hosts of these pests. Coriander positively affected the occurrence of Chrysopidae, Coccinellidae, Staphylinidae, and Aranea, as well as the longevity of parasitoids and the egg-laying of Syrphidae. It also reduced some crop pests. Introduction of the reviewed plants can improve the biodiversity of beneficial entomofauna that can help control pests and reduce diseases, with benefits to crop and yield. The use of synthetic insecticides can thus be greatly reduced, though it is not always possible to avoid them completely.
... Following the LHH, we may expect a lower herbivory pressure in the ex situ populations with higher latitudes and vice versa. Third, the resource concentration hypothesis (RCH) posits greater damage in monocultures (Root, 1973;Stephens & Myers, 2012). As transplanted individuals are monocultures in many ex situ conservation practices, we may expect a higher herbivory rate in ex situ populations, especially those not far from wild populations. ...
Ex situ conservation is an effective approach to prevent the extinction of endangered species. Biotic interactions (e.g. herbivory and pollination) are critical to ex situ conservation success, including plant establishment, survival and reproduction. However, shifts in biotic interactions between wild and ex situ populations are still poorly understood.
We compared herbivory and pollination characteristics between the only wild population (WP) and three ex situ populations (LP, local population, nearby WP; NP, north population, ca. 850 km; and SP, south population, ca. 750 km) of a critically endangered tree species (Sinojackia huangmeiensis) to explore the latitudinal changes in plant‐invertebrate interactions.
Larvae of the Limacodidae family were the dominant herbivores in WP, LP and NP, while the only herbivore observed in SP was snail. Compared to WP, the leaf herbivory rate was unchanged in LP but decreased in NP and SP. Leaf defence traits (total phenols, tannins, leaf thickness and leaf dry matter content) increased or remained unchanged in the three ex situ populations. A pollinator (Apis cerana) of S. huangmeiensis was present in the four populations. NP and SP lacked some pollinators that were found in both WP and LP, but they shared one pollinator that was not observed in WP and LP. The pollinator visiting frequency increased in SP, while it did not change significantly in LP and NP.
Synthesis and applications. Our results suggested that both herbivory and pollination of Sinojackia huangmeiensis changed in ex situ populations, with complete or partial changes in herbivores, leaf herbivory rate, pollinators, pollinator visiting frequency and fruit set in the two distant ex situ populations. This work provides a unique empirical study of shifts in both antagonistic and mutualistic biotic interactions between wild and ex situ populations. We emphasized that it is essential to integrate herbivore and pollinator management in future ex situ conservation of plant species.
... Specialista növényevő rovarokról általánosságban elmondható, hogy kártételük monokultúrákban szignifikánsan jelentősebb mértékű, mint elegyes állományokban (Jactel et al. 2021). Két hipotézis magyarázhatja ezt a hatást: az egyik a természetes ellenségek hipotézise, míg a másik a forrás koncentráció hipotézis (Root 1973). Mivel a tölgy-csipkéspoloskára gyakorolt ragadozó nyomás elenyésző (Paulin et al. 2020), így nem releváns a természetes ellenségek hipotézise, ami szerint a ragadozók egy komplexebb környezetben hatékonyabbak (Russell 1989). ...
A tölgy-csipkéspoloska tömeges fellépése jelentős hatással lehet tölgyeseink egészségi állapotára, növedékére, makktermésére és a tölgyesekhez kapcsolódó közösségekre. Nagy távolságra történő terjedését elsősorban a közúti és vasúti forgalom segíti elő, míg kisebb távolságokra aktívan és passzívan egyaránt képes eljutni. Rövid távú terjedését befolyásoló tényezők lehetnek a fertőzési forrástól való távolság, az elegyesség, vagy az uralkodó szélirány. Specialista lombfogyasztókra (különösen a tápnövényt aktívan keresőkre) jellemző, hogy ha tápnövényük elegyben található meg, akkor azt nehezebben találják meg, így terjedésük lassabb, illetve korlátozott. Eredményeink azt mutatják, hogy kezdetben az utak szegélyeiben keletkeznek nagyobb fertőzési gócok, a fertőzés innen halad az állományok belseje felé. Az elegyes erdők nem képesek érdemben lassítani a C. arcuata invázióját, valamint az uralkodó széliránnyal ellentétes irányba is képes a faj terjedni.
... Our study reinforces the role of predators on suppression of terrestrial herbivore populations [65,66] and demonstrates the importance of predators as a biological control agent in a variety of crop systems. This result also highlights that predators could reduce pest populations and increasing yield even in crop systems, which tend to be simpler environments than natural or semi-natural habitats and could lead to more strong species interactions ( [67], but see for example enemies' hypothesis: [68,69]). Although the influence of landscape context on biological control is outside the scope of our study, other possible explanations might be that landscape complexity at different scales is also important for biological control, and pest control in crops inserted in complex landscapes may benefit from additional resources [70,71]. ...
Pesticides have well-documented negative consequences to control crop pests, and natural predators are alternatives and can provide an ecosystem service as biological control agents. However, there remains considerable uncertainty regarding whether such biological control can be a widely applicable solution, especially given ongoing climatic variation and climate change. Here, we performed a meta-analysis focused on field studies with natural predators to explore broadly whether and how predators might control pests and in turn increase yield. We also contrasted across studies pest suppression by a single and multiple predators and how climate influence biological control. Predators reduced pest populations by 73% on average, and increased crop yield by 25% on average. Surprisingly, the impact of predators did not depend on whether there were many or a single predator species. Precipitation seasonality was a key climatic influence on biological control: as seasonality increased, the impact of predators on pest populations increased. Taken together, the positive contribution of predators in controlling pests and increasing yield, and the consistency of such responses in the face of precipitation variability, suggest that biocontrol has the potential to be an important part of pest management and increasing food supplies as the planet precipitation patterns become increasingly variable.
... For biocontrol agent establishment, life history traits of the agent may be more important than traits of the respective target weed. Because biocontrol agents are introduced and released in a more enemy-free environment with unlimited host resources, it has been argued that weed traits are less important factors affecting the probability of agent establishment (Root 1973;Kéry et al. 2001;Sholes 2008;Stephens and Myers 2012). Although we did not explicitly test the importance of agent traits vs. plant traits, our results anecdotally support this argument in that six of eight biocontrol agent life history traits included in this analysis were strongly associated with establishment, while this was true for only one of four target weed traits analyzed. ...
Improving success rates of classical weed biocontrol programs is an ongoing effort that requires a variety of different approaches. Previous assessments indicated biocontrol agent taxonomy and feeding characteristics and weed life history traits are associated with better control outcomes. We examined weed biocontrol releases for correlations between biocontrol agent and target weed traits associated with different levels of reported establishment and control. Data collated in the 5th edition of ‘Biological Control of Weeds: A World Catalogue of Agents and Their Target Weeds’ were used as the basis for this global analysis. Published literature was used to augment the catalog with data for eight biocontrol agent traits and four target weed traits. Biocontrol agent establishment and impact data were analyzed against these traits using generalized linear mixed models and categorical models, respectively. Analyses for biocontrol agent establishment reveal the following agent traits were correlated with a greater probability of establishment: being an internal feeder, feeding on above-ground plant tissues, multivoltine agents and agents that feed during both their adult and immature life stages. Insect taxon did not affect establishment except for the order Lepidoptera, which had the lowest establishment probability. For weed traits, those occurring in aquatic or riparian habitats were associated with a higher probability of biocontrol agent establishment. Regarding agent impact, using the definition categories in the catalog, agents feeding externally and on vegetative plant tissues, multivoltine agents and those with both adult and immature plant-feeding life stages were strongly correlated with greater impact. Perennials, reproducing only vegetatively and invading aquatic or riparian habitats were associated with greater biocontrol impact. Our findings could facilitate both the prioritization of invasive plants targeted for biocontrol and the selection of suitable biocontrol agent candidates, which should further improve biocontrol project outcomes.
... This weaker effect of land-use predictors is consistent with the results of Hof and Allen 37 and Gong et al. 40 Nevertheless, Liu et al. observed contrasting patterns in the relative effects of land-use and climatic conditions on the potential ranges of the fall armyworm (a globally invasive pest) at the global scale, and this might be explained by the resource concentration hypothesis, which posits that pests tend to occupy portions of their potential range with high resource abundance. 41,42 Thus, the relative effects of climate and land-use changes on potential ranges are likely species-specific, 40 and several mechanisms might affect the relative importance of these factors. Further investigation is needed to clarify the relative importance of the effects of climatic and land-use changes on the potential ranges of alien invasive species. ...
BACKGROUND
The invasion of Asian yellow‐legged hornets (Vespa velutina) has significantly affected Western honey bees (Apis mellifera) and apiculture in Europe. However, the range dynamics of this hornet and its range overlap with the bees under future change scenarios have not yet been clarified. Using land‐use, climate, and topographical datasets, we projected the range dynamics of this hornet and Western honey bees in Europe and the future overlap of their ranges.
RESULTS
We found that climatic factors had stronger effects on the potential ranges of the hornets compared with land‐use and topographical factors. A considerable range expansion of this hornet was predicted, and an increase in the overlap between this pest and the bees was primarily caused by future decreases in temperature seasonality. Additionally, we detected future range expansions of the hornet in the UK and France; future range overlap between this pest and Western honey bees in the UK, Ireland, Portugal, and France; and future overlap between the ranges of this pest and bees but not under recent conditions was mainly projected in Germany, Denmark, and the UK.
CONCLUSION
Mitigating future climate change might effectively control the proliferation of the hornets and their effects on the bees. Strategies for preventing the invasion of this pest and developing European apiculture should be developed and implemented in these regions where future range overlap between them was projected. Given that climate‐change scenarios may result in uncertainty in our projections, further investigation is needed to clarify future range changes of our target species. © 2024 Society of Chemical Industry.
... Sebagian besar spesies tumbuhan yang memanfaatkan hewan untuk menyebarkan serbuk sarinya memiliki sifat yang sama antara satu tumbuhan dengan tumbuhan lainnya, meliputi warna bunga, bentuk bunga, dan aroma yang tentunya akan menarik hewan untuk menghampirinya. Misalnya, burung Kolibri (Trochilidae) yang aktif di siang hari memiliki penglihatan warna yang sangat baik, paruh yang 71 Disebut juga zaman jurasik, yaitu periode utama dalam skala waktu geologi yang berlangsung antara 201,3 juta tahun sampai 145 juta tahun yang lalu 72 [111]. Saling ketergantungan ini mengasumsikan populasi tumbuhan Ara memerlukan kepadatan yang tinggi agar dapat mempertahankan eksistensi spesiesnya [112]. ...
Dalam eksplorasi ilmu tumbuhan, kita disuguhkan dengan
keberagaman dan keelokan flora yang memperindah bumi
kita. Tumbuhan, dengan kekayaan spesies dan sifat yang
unik, membuka tirai keajaiban alam selama ini. Tidak hanya
mengungkap kompleksitas dan pesona keindahan, interaksinya dengan
fauna di sekitar juga menggambarkan sebuah peta kehidupan yang tak
terduga. Dari kerja keras lebah yang menjelajahi nektar hingga
kehadiran burung yang mencari pelindung di bawah kanopi dedaunan,
setiap organisme memiliki peran pentingnya dalam menyelaraskan
harmoni ekosistem. Selain itu, kita juga tidak hanya memahami
keberagaman organ-organ dasar tumbuhan, melainkan juga menggali
organ tambahan yang unik dan peran mereka dalam berinteraksi
dengan lingkungan sekitar. Dari kantong hingga umbi, setiap struktur
ini memiliki perannya masing-masing dalam kelangsungan hidupnya.
Sejalan dengan eksplorasi ini, kita diingatkan bahwa keajaiban
dunia tumbuhan dapat didekati secara ilmiah. Melalui metode ilmiah
yang cermat, kita dapat mendalami pengetahuan dan memahami
morfologi, anatomi, fisiologi hingga genetika tumbuhan yang selama
beberapa tahun terakhir terus berkembang. Penelitian dan pendekatan
ilmiah sangat dibutuhkan untuk membuka jalan menuju kebaruan, dan
menggelar pengetahuan dan wawasan yang lebih luas.
Buku ilmiah populer ini setidaknya dapat menjadi asupan
tambahan tentang pemahaman, gambaran dan informasi terkait teori
mengenai tumbuhan dan interaksinya dengan hewan. Tentu, diulas
dengan perspektif dan cara pandang yang berbeda sehingga ringan
dibaca namun tetap ilmiah. Semoga buku ini tetap memberikan aroma
ilmu pengetahuan yang melekat dan menjadi buku pendamping
bersama buku-buku sejenis lainnya.
Emerald ash borer (EAB) (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) is the most destructive insect to invade North American forests. Identifying habitat features that support EAB natural enemies is necessary to enhance EAB biological control. In many forest ecosystems, tree species diversity has been linked with reduced pest abundance and increases in natural enemy abundance. We assessed the influence of tree species richness, ash density, and proportion of total ash basal area on ash canopy condition, EAB larval densities, and biocontrol by woodpeckers and parasitoids in pairs of healthy and declining overstory (DBH > 10 cm) and recruit-sized ash (DBH 2–10 cm) in 4 post-invasion forests in Michigan, USA. Tree species richness and ash density were not significantly associated with EAB larval densities, ash canopy dieback and transparency, and woodpecker predation of EAB larvae. In declining and healthy overstory ash, woodpeckers killed 38.5 ± 3.9% and 13.2 ± 3.7% of larvae, respectively, while the native parasitoid Phasgonophora sulcata Westwood killed 15.8 ± 3.8% and 8.3 ± 3.0% and the introduced parasitoid Spathius galinae Belokobylskij & Strazanac killed 10.8 ± 2.5% and 5.0 ± 2.6% of EAB larvae. Parasitism by P. sulcata was inversely related to ash density while parasitism by S. galinae was positively associated with ash density. Ash density, but not tree diversity, appears to differentially influence biological control of EAB by parasitoids, but this effect is not associated with reduced EAB densities or improved canopy condition.
Push-pull strategy in integrated pest management (IPM) is employed for controlling aphid population as the aphid produces deleterious damage to crops. For wheat aphid management, wheat (Triticum aestivum) and peas (Pisum sativum) were scrutinized to observe pest and predator population and peas act as the stimuli that allure the aphids (pull). In this study the pea-wheat trap crop area was divided into control (pea and wheat) and experimental (wheat sandwiched between peas) zones with an area of 0.13 acres (0.0526 hectare). The purpose was to determine natural abundance of Aphids in peas and wheat, Population abundance of natural enemies attacking aphids in peas and wheat and comparison of abundance of natural enemies and aphids in peas and wheat. Pea-wheat trials were surveyed on a weekly basis by visual observation utilizing five fixed sampling methods. Results indicated the mean number of aphid population was 54.77 in wheat control zone while in experimental zone 63.79 per 100 tillers while predat ors in experimental zone were 767.72 and control had 82.99 per 100 tillers. Moreover, peas considered as pull had an aphid population in control zone was 937.83 and experimental had 1147.56 per 100 plants whereas, predator in control was 33.50 and in experimental 8.66 per 100 plants. The research findings statistically showed that the population abundance of predators was 8.66 in the experimental zone for peas and 82.99 in wheat, attacking aphids in the peas and wheat ecosystem. The population abundance of predators was determined in peas and wheat, with the higher population observed in wheat compared to the peas. Thus, it can be concluded peas proved beneficial in reducing aphid population from main crop without aid of pesticides, on the basis of present research underpin the existing knowledge on Trap crop in IPM.
Premise
Theories of plant–herbivore interactions hold that seedlings are more vulnerable to herbivory in warmer and more stable climates at lower elevations. Hypotheses of plant apparency, resource concentration, and resource availability have been proposed to explain variability in leaf herbivory. However, seasonal differences in the effects of these hypotheses on leaf herbivory on seedlings remain unclear.
Methods
We evaluated the three herbivory hypotheses by comparing the percentage and frequency of leaf herbivory in understory broadleaf seedlings in a subtropical forest in May (spring) and October (autumn) along an elevational gradient (290–1370 m a.s.l.). In total, we measured 2890 leaves across 696 seedlings belonging to 95 species and used beta regressions to test the effects of plant apparency (e.g., leaf area, seedling height), resource concentration (e.g., plant species diversity), and resource availability (e.g., canopy openness, soil available N and P) on leaf herbivory.
Results
Seedlings exhibited unimodal patterns of leaf herbivory along elevation, with drivers of leaf herbivory varying by the month. Variation in the frequency of leaf herbivory was best explained by the resource concentration hypothesis (e.g., plant species diversity) in both months, and herbivory was lower on seedlings in sites with higher plant diversity. Plant apparency hypothesis (e.g., leaf area, seedling height) was weakly supported only in spring, and the evidence for resource availability hypothesis (e.g., canopy openness, soil nutrients) was mixed.
Conclusions
This study supports the resource concentration hypothesis and reveals the importance of seasonal difference on understanding leaf herbivory patterns and the drivers of plant diversity in subtropical forests.
Declines in biodiversity generated by anthropogenic stressors at both species and population levels can alter emergent processes instrumental to ecosystem function and resilience. As such, understanding the role of biodiversity in ecosystem function and its response to climate perturbation is increasingly important, especially in tropical systems where responses to changes in biodiversity are less predictable and more challenging to assess experimentally. Using large-scale transplant experiments conducted at five neotropical sites, we documented the impacts of changes in intraspecific and interspecific plant richness in the genus Piper on insect herbivory, insect richness, and ecosystem resilience to perturbations in water availability. We found that reductions of both intraspecific and interspecific Piper diversity had measurable and site-specific effects on herbivory, herbivorous insect richness, and plant mortality. The responses of these ecosystem-relevant processes to reduced intraspecific Piper richness were often similar in magnitude to the effects of reduced interspecific richness. Increased water availability reduced herbivory by 4.2% overall, and the response of herbivorous insect richness and herbivory to water availability were altered by both intra- and interspecific richness in a site-dependent manner. Our results underscore the role of intraspecific and interspecific richness as foundations of ecosystem function and the importance of community and location-specific contingencies in controlling function in complex tropical systems.
Neighbouring plant species can indirectly affect each other's fitness through insect herbivores. For instance, the number of eggs an insect deposits on a focal plant can be influenced by the presence of a neighbouring plant species because of the herbivore's relative host plant preferences. Yet, the relationship between oviposition preferences (measured in no‐choice tests) and the strength and direction of such indirect effects among neighbouring plants remains poorly understood.
We performed a lab experiment using bean beetles ( Callosobruchus maculatus ) and five species of beans to determine if beetles' no‐choice preferences for a neighbouring bean species correlated with the number of eggs laid on a focal species in two‐species environments (diculture).
We predicted that as the preference for the neighbouring beans increased compared to the focal host, beetles would lay fewer eggs on the focal bean host.
Across all pair‐wise combinations, our prediction was supported: as the relative no‐choice preference of neighbouring beans increased, the number of eggs laid on focal beans decreased. However, this relationship was relatively weak. We also found that beetles tended to lay more eggs in diculture compared to arenas with one bean species.
These results provide empirical evidence linking herbivores' no‐choice preferences to the strength of neighbourhood effects and suggest that even within a relatively controlled environment, neighbourhood effects can be weak. Our results also highlight that unexpected changes to the total number of eggs laid by herbivores in mixed‐plant patches relative to monoculture can complicate predictions.
Weed management is challenging for vegetable crops that are highly sensitive to weed competition, such as onions. Thrips (Thysanoptera: Thripidae) are major insect pests of onions, causing damage through feeding, and vectoring bacterial pathogens causing bulb rot. Both thrips and their associated pathogens are known to survive on many weed species in onion growing regions. Combining weeding with biopesticides may synergistically manage thrips and reduce disease prevalence. However, disturbances from weeding may negatively impact natural enemies. We estimated the effects of organic weed management and biopesticides on weed density, thrips and natural enemy activity, disease severity, and yield. The experiment was a randomized complete block design, with 4 replications of each weeding (control, tine-weeded twice, tine-weeded 4 times, and hand-weeded) and biopesticide (control, OxiDate 2.0, Serenade) combination. Arthropods were monitored using yellow sticky cards, and weed counts, marketable yield, and bulb rot prevalence were estimated. Hand-weeding resulted in the lowest weed density and thrips abundance. Additionally, hand-weeding produced a 9× higher yield compared to all other treatments. Significant interactions were observed between tine-weeding and biopesticide treatments on the prevalence of bulb rot. Natural enemy abundance was slightly negatively impacted by weeding, dependent on the year. DNA metabarcoding results showed high parasitoid diversity in this onion system and high numbers of reads for multiple genera containing important known biological control agents. Our study suggests hand-weeding is necessary in the southeast for maximum onion yield. Future research should focus on exploring the impact of management on natural enemy communities in onion systems on a large scale.
The two volumes of this handbook provide a comprehensive account of the emerging and vibrant science of the ecological restoration of both habitats and species. Ecological restoration aims to achieve complete structural and functional, self-maintaining biological integrity following disturbance. In practice, any theoretical model is modified by a number of economic, social and ecological constraints. Consequently, material that might be considered as rehabilitation, enhancement, re-construction or re-creation is also included. Principles of Restoration defines the underlying principles of restoration ecology, in relation to manipulations and management of the biological, geophysical and chemical framework. The accompanying volume, Restoration in Practice, provides details of state-of-the-art restoration practice in a range of biomes within terrestrial and aquatic ecosystems. The Handbook of Ecological Restoration will be an invaluable resource to anyone concerned with the restoration, rehabilitation, enhancement or creation of habitats in aquatic or terrestrial systems, throughout the world.
The two volumes of this handbook provide a comprehensive account of the emerging and vibrant science of the ecological restoration of both habitats and species. Ecological restoration aims to achieve complete structural and functional, self-maintaining biological integrity following disturbance. In practice, any theoretical model is modified by a number of economic, social and ecological constraints. Consequently, material that might be considered as rehabilitation, enhancement, re-construction or re-creation is also included. Principles of Restoration defines the underlying principles of restoration ecology, in relation to manipulations and management of the biological, geophysical and chemical framework. The accompanying volume, Restoration in Practice, provides details of state-of-the-art restoration practice in a range of biomes within terrestrial and aquatic ecosystems. The Handbook of Ecological Restoration will be an invaluable resource to anyone concerned with the restoration, rehabilitation, enhancement or creation of habitats in aquatic or terrestrial systems, throughout the world.
The two volumes of this handbook provide a comprehensive account of the emerging and vibrant science of the ecological restoration of both habitats and species. Ecological restoration aims to achieve complete structural and functional, self-maintaining biological integrity following disturbance. In practice, any theoretical model is modified by a number of economic, social and ecological constraints. Consequently, material that might be considered as rehabilitation, enhancement, re-construction or re-creation is also included. Principles of Restoration defines the underlying principles of restoration ecology, in relation to manipulations and management of the biological, geophysical and chemical framework. The accompanying volume, Restoration in Practice, provides details of state-of-the-art restoration practice in a range of biomes within terrestrial and aquatic ecosystems. The Handbook of Ecological Restoration will be an invaluable resource to anyone concerned with the restoration, rehabilitation, enhancement or creation of habitats in aquatic or terrestrial systems, throughout the world.
Habitat manipulation such as intercropping can be used as a simple and common cultural practice in pest management. This method is based on the principle of reducing pest populations by increasing the diversity of an ecosystem. This study has been carried out to evaluate the influence of additive series intercropping common bean with some aromatic plants (AP), and 2 acaricides on the different life stages (egg, immature mobile stages, and adult) of Tetranychus urticae Koch (Trombidiformes: Tetranychidae), over 2 yr of experimentation (2020 and 2021). This experiment was conducted following a randomized complete block design with 7 treatments including common bean monoculture, common bean sprayed by spiromesifen or Dayabon, and common bean + companion plants (coriander, ajwain, basil, or dill). Each treatment was replicated 3 replicates. The lowest and highest number of eggs, immature mobile stages, and adults were observed in common bean + spiromesifen and the common bean monoculture, respectively. Additionally, the common bean + Dayabon supported significantly different T. urticae life stage densities compared to common bean monoculture. Also, among intercropped treatments, common bean + basil showed the lowest number of T. urticae (eggs, immature mobile stages, and adults). The highest yield and land equivalent ratio were recorded in common bean + basil and common bean + spiromesifen, respectively. Finally, it can be concluded that additive intercropping with these AP can effectively decrease the T. urticae population density, which is useful for the safe production of common bean.
The lepidopteran fauna on goldenrod, Solidago altissima, in central New York is extraordinarily diverse (63 species in 43 genera and 13 families, representing 61% of the total insect fauna on S. altissima), as determined through over four years of sampling at 43 sites. To best illustrate the functional structure of the community, caterpillars are divided into both feeding and sheltering guilds. We studied patterns in caterpillar size, feeding guild, sheltering guild, host range, phenology, abundance, and taxonomic relationships to gain insights about community assembly on this group of native caterpillars on a prominent native host species. Size distribution among caterpillar species is highly skewed toward the small end and does not differ between caterpillars with broad and narrow host ranges. There are relatively few species that feed on stems and rhizomes, suggesting challenges in adapting to those plant parts. Host range is a highly conserved trait in several lineages of goldenrod feeders (relatives of polyphagous species are polyphagous, and relatives of specialists are specialists). Polyphagous species and exposed-feeding species are usually rare; some specialist species are also chronically rare. There is a dearth of species in mid-summer, between the time that many leaf-folding and leaf-tying species complete development and the time that flower-feeding species appear. Species with high intimacy of association (gallmakers, stem borers, and leaf miners) tend to be specialists, as compared with exposed feeders, and they are necessarily small in size. Among exophages, size relations are constrained by phylogeny. Lineages have characteristic behaviors and means of association with the host; as a result, the structure of the fauna is determined by an interaction of ecological factors and evolved constraints in the lineages that have adapted to feed on Solidago.
Plant diversification contributes to the ecological intensification of agroecosystems through pest biocontrol services provision. However, the existing evidence for the effectiveness of plant diversification in enhancing pest biocontrol services is highly uncertain across features of plant diversity and biodiversity characteristics. We undertook a comparative meta-analysis focusing on three essential crops (wheat, maize, and soybean) to investigate how diversification schemes in-field (intercropping) and Agri-environmental scheme (AES) around the field (flower strip, hedgerow and field margin) affect arthropod abundance. A random effects analysis was used to determine the role of 10 key factors underlying the effectiveness of plant diversification including biodiversity level and habitat, main and companion plant species, intercropping arrangement, the growth stage of the main crops, type of AES planting scheme, AES planting width, distance from AES plantings and geographical latitude. The overall results revealed that intercropping reduced herbivore and boosted predators and parasitoids abundance significantly, while AES successfully increased predators but not herbivores. Maize intercropping with legume and non-legume plants and row intercropping allowed for effective pest management. The abundance of predators increased in wheat fields immediately adjacent to planting around the field (AES), but this effect declined beyond 5 m from the flower strips. Our results suggest that the response of arthropod abundance to plant diversification is a compromise between spatial management scale, ecological characteristics of arthropod and plant diversification features. These results offer promising pathways for optimizing plant diversification schemes that include functional farm biodiversity across spatial and temporal scales and designing multi-functional landscapes.
The effect of removal of the bottom flora in a hawthorn hedgerow was investigated in a study of the fauna of the hawthorn over 3 years, 1964-66. The hawthorn fauna showed a reduction in total numbers and biomass in the treated sections of the hedge in the second and third years after treatment. The most marked effect was a reduction in the number of predators. This occurred in all 3 years of the experiment. A more intensive study of the predacious Heteroptera confirmed the treatment effect for this group. One of these species, Anthocoris nemorum, was restricted to hedges during its first generation, but the second was found to occur in some crops.
A system of dimension analysis of woody plants, applied to stand data for the Brookhaven forest, Long Island, permits its characterization. The forest is a woodland of small oaks and pine with an open canopy, of 88% tree coverage and a leaf area ratio of 3.4, admitting sufficient light (13% of incident sunlight) to support a well-developed stratum of low, vacciniaceous shrubs (78% coverage). Net annual production of the community is 856 g/m2 above ground, about 1195 g/m2 above and below ground, hence in the range of other small tree forests of moderately limiting environments; biomass is low, being 6560 g/m2 above ground and 10190 g/m2 above and below ground. Efficiency of net production (relative to incident sunlight energy in the visible spectrum) is 0.91; efficiency of gross production is about 2.22%. The forest is distinctive in its low biomass accumulation ratio (7.7) and massive oak roots, older than the shoots they now bear. Both characteristics are aspects of fire adaptation: the dominant oaks resprout from root systems that survive fires, and the low biomass accumulation ratio reflects the youth (about 45 years) of the present community in the cycle of fire and regrowth.
(1) The structural organization of three intertidal community types was analysed on the basis of relative biomass of the species populations. Original data for upper and lower tide pools on San Juan Island, Washington, and Glynn's (1965) data for the Endocladia-Balanus community of Monterey Bay, California, were used. Lloyd & Ghelardi's (1964) measure of equitability was used with limited success as an index of the distribution of relative abundances for comparison of communities. (2) Results showed consistent structural patterns for all community types examined. On a logarithmic scale, community biomass was divided among a few dominant species, greater numbers of moderately abundant species and a few rare species. These results are as expected if the underlying frequency distribution is lognormal. (3) Groups of similar species, defined either by taxonomic or functional criteria, tended to have higher equitability indices than groups of dissimilar species. The higher indices indicated relatively less dominance by the common species. (4) A general scheme of animal distribution based on environmental gradient concepts was proposed as an explanatory model for the low equitability indices and the lognormal biomass distributions of whole communities.
@'Switching@' in predators which attack several prey species potentially can stabilize the numbers in prey populations. In switching, the number of attacks upon a species is disproportionately large when the species is abundant relative to other prey, and disproportionately small when the species is relatively rare. The null case for two prey species can be written: P"1/P"2 = cN"1/N"2, where P"1/P"2 is the ratio of the two prey expected in the diet, N"1/N"2 is the ratio given and c is a proportionality constant. Predators were sea-shore snails and prey were mussels and barnacles. Experiments in the laboratory modelled aspects of various natural situations. When the predator had a strong preference (c) between prey the data and the @'null case@' model were in good agreement. Preference could not altered by subjecting predators to training regimens. When preference was weak the data did not fit the model replicates were variable. Predators could be trained easily to one or other prey species. From a number of experiments it was concluded that in the weak-preference case no switch would occur in nature except where there is an opportunity for predators to become trained to the abundant species. A patchy distribution of the abundant prey could provide this opportunity. Given one prey species, snails caused a decreasing percentage mortality as prey numbers increased. This occurred also with 2 prey species present when preference was strong. When preference was weak the form of the response was unclear. When switching occurred the percentage prey mortality increased with prey density, giving potentially stabilizing mortality. The consequences of these conclusions for prey population regulation and for diversity are discussed.
The presence of weed within the crop provides a habitat which is more suitable for some of the arthropod predators of Pieris rapae. Harpalus rufipes is particularly dependent on ground-cover. With the higher number of predators, survival of Pieris caterpillars was significantly poorer (P<0.01) on weedy than on hoed plots. Fewer eggs were laid by Pieris on those plots with many flowering weeds, but the difference was not significant to the 5% level. Pest numbers were low and the advantageous effects of weed were outweighed by the harmful effect of competition between the weed and the crop. Yield was highest on those plots which were kept free of weed.
The patterns of distribution, of insects flying over pasture, to leeward of a mixed hedge were measured with suction traps. Insects in the hedgerow and neighbouring fields were sampled with a vacuum sampler to show the probable origin of some taxa within the aerial populations. The patterns for insects drifting over the hedge from distant sources resembled patterns near artificial windbreaks of similar permeability, with accumulations extending about ten times the height of the hedge to leeward, and with the greatest density at about 2-4 H to leeward. Patterns for insects originating in the hedge were quite different, with accumulations extending a shorter distance to leeward and with greatest densities immediately behind the hedge. Whatever their origin, fewer insects accumulated in slow winds than in fast, which suggests that accumulations near hedges occur largely because the patterns of air-flow created by the hedge concentrate insects from the passing aerial population, not because the hedge itself supplies the greater population.
A distinction is made between immigration rate (in spp./time) for an island, and invasion rate (in propagules/time) for a species and an island. An analogous distinction is drawn between an island extinction rate and a species extinction rate (or intrinsic probability of extinction in a given time interval). It is claimed that the most objective definition for @'propagule@' is any animal of group capable of population increase under any conceivable circumstances. Immigration and island extinction curves are unique only if plotted against time, not against number of species. A model for non-interactive colonization is discussed, and its equilibrium number of species, @? derived. It is shown that data from the defaunated Florida Keys can be interpreted as arising from non-interactive colonization to an @? near the non-interactive @? (and to a point above a more enduring interactive @?), followed by a slow decline in @? (as population sizes and interaction increase) to an enduring @? near that obtaining before defaunation. The effect on this scheme of increasing distance from source area is shown, and a simulation of the non-interactive part of the scheme was performed with corroborates that part of the model. Explicit equations for the @'expected@' colonization, immigration, and island extinction curves are given for non-interactive colonization, and predictions are given about the general changes in these curves as interaction becomes significant.
1. During a long-term study of the insects of the Field Layer of an abandoned field in Michigan, U.S.A., 1584 `resident' species were collected. These represent 179 families in fifteen orders, but 86% belong to the Hymenoptera, Diptera, Lepidoptera and Coleoptera. 2. The general food habits of the larval and adult stages, taken largely from reports in the literature, have been classified and analysed. Thirty-one feeding categories were recognized, of which the Diptera were represented in twenty-three. The great majority of species present on the field were herbivorous as adults and about half were entomophagous (chiefly parasitic) as larvae. Thirteen per cent were found to complete their early life stages in habitats away from the field. 3. The number of species present as adults was relatively small at the beginning (April) and end (October) of the season of activity and was at its peak in late July. The duration of adult occurrence on the field was shown to be related to the type of (adult) feeding habits: flower-feeding species tended to have short-lived adult populations, whereas those which feed on leaves and stems persisted for longer periods. 4. Nearly three-quarters of the Field Layer species, and 86% of those whose adults are herbivorous, were found to feed at flowers. The percentage of flower-feeding species present in successive fortnightly intervals ranged from 45 to 54% throughout most of the season and did not decrease significantly until October. 5. For most of the season, the ratio of the number of species with herbivorous larvae to the number whose larvae are carnivorous was found to be quite stable, suggesting that the feeding relationships impose a structure on the insect community that persists in spite of a continual seasonal replacement of species.
Scotch broom (Sarothamnus scoparius) has been introduced from Europe to the Pacific coast of North America where it has spread and has become a weed. The main broom sites in California and in British Columbia were visited and the insect fauna was examined. Some of the introduced insect species that were found are new records for California or for British Columbia. Most of the introduced insects on broom are those which aestivate or hibernate in their immature stages under bark of young stems. They were probably transported with young host plants which were introduced either deliberately, or accidentally in ballast. The delicate flies Micropeza lateralis and Minettia fasciata were most probably carried over as puparia in broom litter in ballast. The most abundant broom insects in California are the mirid Orthotylus concolor, the moth Leucoptera spartifoliella and the psyllid Arytaina spartiophila. The broom fauna of British Columbia is much richer and the most abundant insect, at the time of my visit, was Orthotylus virescens. The populations of O. concolor in California and of O. virescens in British Columbia are enormous. Their expansion is probably associated with climatic conditions favourable to these species and with the absence of many natural enemies, notably the early hatching broom Miridae which are predacious as well as phytophagous. Samples from populations of broom Miridae from North America were compared with those from southern England. Eight characters were measured and subjected to the canonical variate analysis. The ranges of variation in samples of populations of O. virescens from southern England were as great as those between different geographical regions. O. concolor is a more plastic species, but although its populations may have been isolated for more than a hundred generations in the Sierran foothills, no major departures were found in the characters studied.
This paper is concerned with the community of invertebrates living in small decaying oak logs on the forest floor. The reactions of species' populations to various factors inside and outside the logs were determined by the use of `synthetic logs', models of the habitat whose initial characteristics were known. Comparison of the results from these models with those from natural logs indicates that the former were good substitutes. Forty-five of the 108 species considered showed significant differences in abundances associated with one or more features of the environment. Some of these were expected on the basis of prior knowledge of the species' ecology, others suggest reactions that merit further study. The presence or absence of a reaction was not predictable from knowledge of a species' frequency, median abundance or taxonomic group. The recurrent grouping procedure indicated a major group that may be considered the basic fauna of small decaying oak logs. Smaller groups are added to this, depending on the specific environmental and log characteristics. Although there was a great diversity of dominant species, all the log populations had similar structure. The average synthetic log contained 900 individuals distributed among forty-one species as follows: two species contributed 50% of the individuals (A), three species contributed an additional 25% (C), twenty-four species had two to seventy-four individuals and the remaining twelve species were represented by single individuals (S). Forty-six of the 108 species were at least once in classes (A) or (C) but none was always in this class and only four of these were never in (S). The structure was successfully simulated by a computer model that assumed that frequency is a measure of the probability that a species will invade a log, that rates of increase can be derived from maximum numbers observed per log and that invasion and establishment are random processes.
The effect of removal of the bottom flora of a hawthorn hedgerow on the Carabidae of the hedge bottom was investigated by means of pitfall trapping. Removal of the bottom flora resulted in reduced captures of the majority of carabid species present in the hedgerow. Three of the species studied were virtually restricted to the hedgerow, a further two overwintered there and one was most frequently captured in the barley crop close to the hedge. Another eleven species were apparently independent of the hedge. Agonum dorsale, a common arable species in Huntingdonshire, overwintered in the hedge and bred in the field in summer. An account is given of its seasonal movements between hedge and field at the experimental site.
Phosphorous-32 tracer studies of plant-arthropod food chains showed a significant difference in both consumer diversity and grazing pressure between the two dominant plant species on a first-year weed field in South Carolina. Where Heterotheca subaxillaris was the labeled plant ^3^2P was transferred readily to a number of phytophagous insects and secondarily to the predator fauna. Where only Erigeron canadensis was tagged, there was little transfer of the isotope to the consumer populations, with the exceptions of the ant Dorymyrmex and the tree cricket Oceanthus. Dorymyrmex is a predator-scavenger, but also tends the aphids present on Erigeron; this latter habit accounted for the high uptake and unusual retention pattern of ^3^2P by this ant where Erigeron was tagged. Oecanthus was primarily an herbivore, but the data suggest some predation on aphids from Erigeron plants. Very little ^3^2P was transferred to the detritus eaters during the 43 day period of the study. Further support is given for the use of radioisotope to study trophic position of organisms as well as grazing pressure and food chain diversity associated with single species of terrestrial primary producers.
A corrected formula for alternative (b) of MacArthur's broken stick species-abundance model is described and discussed.
The extent of feeding response of Brevicoryne brassicae (L.) to various chemically-defined liquids has been investigated. The number of aphids settling on the two membranes on the floor of a single-alternative choice chamber were taken as an index of the relative acceptability of the two solutions, and uptake was measured by means of the addition of small quantities of P32 to the solutions. It was found that:
Information content may be used as a measure of the diversity of a many-species biological collection. The diversity of small collections, all of whose members can be identified and counted, is defined by Brillouin's measure of information. With larger collections it becomes necessary to estimate diversity; what is estimated is Shannon's measure of information which is a function of the population proportions of the several species. Different methods of estimation are appropriate for different types of collections. If the collection can be randomly sampled and the total number of species is known, Basharin's formula may be used. With a random sample from a population containing an unknown number of species, Good's method is sometimes applicable. With a patchy population of sessile organisms, such as a plant community, random samples are unobtainable since the contents of a randomly placed quadrat are not a random sample of the parent population. To estimate the diversity of such a community a method is proposed whereby the sample size is progressively increased by addition of new quadrats; as this is done the diversity of the pooled sample increases and then levels off. The mean increment in total diversity that results from enlarging the sample still more then provides an estimate of the diversity per individual in the whole population.
CONCLUSIVE evidence of the properties of plants which determine host selection in aphids has been lacking1. The host plants of the cabbage aphid, Brevicoryne brassicae (L), are restricted to the Cruciferae and Resedaceae2 in which mustard oil glucosides are characteristically present3 and known to stimulate feeding by certain lepidopterous larvæ4. To test the effect of such a substance on B. brassicae, the mustard oil glucoside sinigrin was introduced into young leaves of the broad bean, Vicia faba L., which is not a host of this aphid. The leaves were set with the cut petiole in a 2 per cent aqueous solution of sinigrin for 2 h before and also during each experiment. Apterous virginoparous adult aphids were given a choice between such a sinigrin-treated leaf and a similar but untreated leaf, standing side by side under a 2 × 1 in. glass vial. 45 aphids were used in a total of five experiments. After 24 h an average of 93 per cent of the aphids were found settled and feeding on the sinigrin-treated leaf, with an average of four new-born larvae each. Only two larvæ altogether were found on untreated leaves and the few adults seen there were restless. B. brassicae were reared on sinigrin-impregnated broad bean leaves continuously to the fourth generation when the culture was still healthy.
Linaria vulgaris Miller (Scrophulariaceae) hat sich nach Einschleppung in Nordamerika dort als Unkraut stark ausgebreitet. Daher wird zur Zeit erwogen, die florenfremde Pflanze durch Nachführen von Phytophagen, die im natürlichen Verbreitungsgebiet als biotische Begrenzungsfaktoren wirken, biologisch zu bekämpfen. Dazu ist die Kenntnis der Bionomie der in Europa zur Zoozönose an Linaria vulgaris gehörigen Tierarten Voraussetzung.
Die vorliegenden Untersuchungen sollen als biozönotisch-ökologische Bearbeitung der in Westfalen-Lippe an Linaria vulgaris lebenden phytophagen Insekten einen Beitrag dazu leisten. Dabei wurden Phänologie und Ausbreitungsmodus der Pflanze im notwendigen Ausmaß berücksichtigt. Die Analyse der ökologischen Faktoren, die in Westfalen-Lippe auf Linaria vulgaris einwirken, zeigte, daß Lichtmangel der wichtigste wachstumsbegrenzende abiotische Faktor ist.
Die zahlreichen phytophagen Insektenarten der Entomozönose wurden—gegliedert nach dem überwiegenden Entwicklungssubstrat (Wurzelsystem, Sproßachse, Blätter, Infloreszenz)—bionomisch und ökologisch untersucht. Im Anschluß daran erfolgte die umfassende Bearbeitung der Morphologie, Bionomie und Ökologie von Gymnetron antirrhini Paykull (Col., Curculionidae).
Im Rahmen ökologischer Untersuchungen wurde das Beziehungsgefüge der Choriozönose an Linaria vulgaris aufgezeigt und die Einteilung der vorkommenden Insekten in biozönotische Gruppen vorgenommen. Ferner konnten die Arten nach der Art des biozönotischen Konnexes klassifiziert und ihre Präsenz und Frequenz ermittelt werden. Die zwischenartlichen Korrelationen sind diskutiert und bei den samenvernichtenden Arten quantitativ erfaßt worden. Außerdem wurde kurz auf die Beziehungen zwischen Linaria vulgaris und den vorkommenden cecidogenen Insekten eingegangen.
Zur Diskussion der Möglichkeit einer biologischen Bekämpfung von Linaria vulgaris in Nordamerika durch die in Westfalen-Lippe gefundenen Insektenarten ergab sich: Es erscheint lohnend, Eupithecia linariata Fabricius (Lep., Geometridae) zur Samenvernichtung nachzuführen. Die Monophagie dieser Art wurde durch Fraßversuche nachgewiesen. Brachypterolus pulicarius Linné (Col., Nitidulidae) und Gymnetron antirrhini Paykull (Col., Curculionidae) sind bereits in Canada vorhanden. Zur zusätzlichen Schwächung der physiologischen Leistungskraft von Linaria vulgaris wäre erwägenswert, die an Wurzelhals und Rhizomen gallenbildenden Curculio-niden Gymnetron collinum Gyllenhal und G. linaria Panzer, den Stengel-rüßler Mecinus janthinus Germar sowie die Noctuide Calophasia lunula Hufnagel in Nordamerika anzusiedeln.
Linaria vulgaris Miller (Scrophulariaceae) has been accidentally introduced into North America and has become a noxious weed in certain regions. The biological control of this species in North America by European phytophagous insects is considered. A prerequisite for any attempts at biological control is the biological and ecological study of the complex of phytophagous insects associated with L. vulgaris in Europe. The most important abiotic factor which limits the growth of L. vulguris in the observation area in Westphalia-Lippe is a deficiency in the light intensity. The biology and ecology of the insect species attacking the root, stem axies, leaves and reproductive system of L. vulgaris in Westphalia have been investigated. Detailed studies were made on the morphology, life-history and ecology of Gyrnnetron antirrhini Paykull (Col. Curc.). Data are given on the population density and constancy of the single insect species feeding on the vegetative system of L. vulgaris or destroying its seeds. The interelationships between L. vulgaris and gall-making insects are discussed. The geometrid Eupithecia linariota F., which destroys the seeds, has been exposed to feeding tests and has been found to be monophagous. It may be a promising control agent of L. vulgaris in North America. The leaf-feeding noctuid Calophasia lunula Hufn., the stemboring curculionid Mecinus janthinus Germ., and the curculionids Gymnetron collinum Gyll. and G. linaria Panz., which cause root-galls may merit an intrcduction into North America, because they contribute to a physiological weakening of the host plant.
A suspected chemical means of habitat selection by Diaeretiella rapae, a primary parasite of aphids on crucifer plants, was investigated in the laboratory with the aid of an olfactometer. Females (and, to a lesser extent, males) were found to be attracted by odor to leaves and leaf juices of a crucifer host plant and to dilute solutions of the mustard oil allyl isothiocyanate. Given a choice of aphid colonies (Myzus persicae) on leaves of beet (Chenopodiaceae — mustard oils not present) and collard (Cruciferae — mustard oils present), female D. rapae displayed a marked preference to oviposit in aphids feeding on collard. It is concluded that female D. rapae parasites locate their hosts initially by a response to an odor emanating from the aphid host-plant, followed by visual searching. Male D. rapae were attracted by odor from female D. rapae, suggesting the existence of a sex pheromone in this species.Neither males nor females of Charips brassicae, a hyperparasite of D. rapae, were attracted to collard leaves, though females showed apparent attraction to female D. rapae. As with D. rapae, males of C. brassicae are attracted by odor to females of the same species.The host finding behavior of D. rapae is discussed in relation to that of other insect species belonging to the fauna associated with the plant family Cruciferae.
Longevity and fecundity data are presented for cohorts of cabbage aphid, Brevicoryne brassicae (L.), reared on different hosts (Barbarea vulgaris, Brassica pekinensis, and two varieties of Brassica oleracea) and under constant and fluctuating environmental conditions. Changes in fecundity and development were the chief causes for the different rates of population increase (r) observed on each host. Alate forms developed only in the cohort reared on B. vulgaris, the most resistant host studied. Host factors, acting during the late prenatal period or during postnatal development, appear to be capable of influencing form determination in this aphid.
Community organization is defined as the mean number of trophic links connecting species of different trophic levels in a community. For the special purposes of this paper, competition is assumed to occur whenever two species are known to eat the same food species. Community stability is defined as the reciprocal of the mean, for all species, of the standard error of logarithms of annual collection sizes. It is thus a measure of stability over time of the species populations in a community. Several authors writing about the relationship between community organization and community stability have insisted that the stability of a complex ecological system increases with the number of avenues by which energy can flow through it. This theory does not seem consistent with the observation that some insect pest species of notorious instability are attacked by a great number of entomophagous species. In this paper we seek additional evidence bearing on the relationship between community organization and stability, using computer analysis of data collected by the Canadian Forest Insect Survey on forest Macrolepidoptera and their food plants. After considering our results, and those of other workers, we postulate the following hypothesis. Stability at any herbivore or carnivore trophic level increases with the number of competitor species at that level, decreases with the number of competitor species that feed upon it, and decreases with the proportion of the environment containing useful food. If this hypothesis is valid, too much competition in the entomophagous trophic level will not allow the species in that level to be instable enough to control an unstable pest. Therefore, the best type of biological control agent is one that has no direct competitor species. Also, the most unstable biological control agents, and hence those capable of controlling an unstable pest, will be polyphagous.
In 1958, intensive studies on the population dynamics of the imported cabbageworm,
Pieris rapae
(L.), on cabbage were initiated in long-term study plots at Merivale, Ontario. The object was to construct ecological life tables for successive generations of the species, and ultimately, to develop mathematical models describing survival of field populations. This paper reports on the variation between samples of immature stages of the insect, and between some of the mortality factors affecting its abundance; it further illustrates the use of these data in designing a sampling plan with acceptable limits of precision.
It is universally recognized that the spatial distribution or pattern of animals and plants in nature is neither uniform nor truly random. In order to study a biological community quantitatively, or to assess the densities of living organisms in their habitats, ecologists have found it profitable to sample the space in which the organisms occur. The distribution of the number of individuals per sample is of fundamental importance.
Earlier work indicated that food plants of the tenthredinid sawflies attacked by Drino bohemica Mesn. and Bessa harveyi Tns. influence host-finding by these tachinid parasites (Monteith, 1955, 1958a). There is a high degree of interaction between stimuli produced by the host larvae and by their food plants (Monteith, 1955, 1958b).
It was observed during field studies that the percentage parastism by B. harveyi of the larch sawfly, Pristiphora erichsonii (Htg.), varied with increasing height above the ground and in different sections of tamarack trees, Larix larician (DuRoi) K. Koch, on which the sawfly larvae were feeding. It appeared that shrubs and trees other than L. laricina influenced host-finding by B. harveyi .
Three questions are asked in this paper.
(1) Is the numerical stability of an insect species through time a function of the number of species of food eaten by that species?
(2) Is the information content of a genus related to the stability of species in the genus?
(3) Is the information content of an insect genus related to the number of species of food eaten by the species in that genus?
Data in the Canadian Forest Insect Survey bulletins on Forest Macrolepidoptera are used to answer all three questions; data on parasitic Hymenoptera stored in museums are used to answer the third question. There is some indication that stability decreases with number of host species, and that information content of a genus is less, the less the stability of the species it contains. The evidence from both bodies of data suggests that information content of a genus is less, the greater the average number of species of food eaten by the species in the genus.
The diamondback moth, Plutella maculipennis (Curt.), is one of three species of Lepidoptera that annually cause serious commercial damage to cabbage and related crops in Ontario. It has long been underrated as a pest of cruciferous crops, possibly because of its small size; in eastern Ontario, it is much more numerous than the other two species and ranks second in importance to the imported cabbageworm, Pieris rapae (L.) (Harcourt et al. , 1955). Its biology in eastern Ontario was investigated from 1951 to 1956. The history, distribution, and synonomy of the insect and general descriptions of the stages were given earlier (Harcourt, 1956). This article presents the life-history, behaviour, and host relationships.
Plant phenolics are a structurally diverse group of compounds synthesized by all higher plants. The toxicity of phenolics and the products of their hydrolysis and oxidation has long been appreciated, and has implicated this group of natural products with plant defense. Unfortunately, much of the literature relating phenolics to plant defense is published in sources rarely consulted by evolutionists or ecologists. The purpose of this paper is to make a case for plant phenolics as defensive substances by considering their structural diversity, concentration, alteration upon infection, and mode of action. Correlations between ecogeographical and ecological parameters and phenolic profiles are discussed in light of the putative defensive role of phenolics, and additional correlations are predicted.
These experiments were designed to determine the degree and kind of variability in the structure of the community that one might expect under very similar ecological conditions. The results of these experiments show that 95.5% to 98.0% of the specimens composed the same species in the eight communities. About 5% of the specimens were in the remaining species in one series of experiments and 1% to 2% of the species in the second series. The Shannon-Weaver diversity indices and the structures of the truncated log-normal curves representing the communities in a given series were also very similar.
The role played by the space-time structure of the environment in the survival of the wasp (Nasonia vitripennis) parasite-fly (Musca domestica and Phaenicia sericata) host systems was studied in the laboratory using a special population cage which consisted of a group of interconnected cells. One 30-cell parasite-host system survived for longer than a year. Increasing the number of cells from 16 to 30 in the population cage, decreased the average density of parasites and hosts per cell, but increased the chances of survival of the system. The amplitude of the fluctuations of the parasite-host populations did not increase with time as proposed by Nicholson's theoretical models but was limited by intraspecific competition. The rapid rate of evolution which occurred was the most important aspect of the experimental parasite-host populations. Within eight generations in a 16-cell system, reproductive capacity of the parasite declined 40 per cent. In 20 generations in a 30-cell system, reproductive capacity of the parasite declined 68 per cent. Such important qualitative changes in the parasite and host populations influenced the population characteristics of the systems to some degree. This demonstrates the importance of considering qualitative changes in studies of population dynamics of all herbivore-plant, predator-prey, and parasite-host systems.
Much as Rachel Carson's "Silent Spring" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic "The Ecology of Invasions by Animals and Plants" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. "History has caught up with Charles Elton's foresight, and "The Ecology of Invasions" can now be seen as one of the central scientific books of our century."-David Quammen, from the Foreword to "Killer Algae: The True Tale of a Biological Invasion"
A study was made of aphidophagous syrphids and syrphid predation on Brevicoryne brassicae on brussels sprouts in contrasting areas of farmland. One area was rich in hedges, woodland, pasture and other habitats outside the crop and the other was mainly arable. The areas were 5 km apart. The work was divided into three parts. (1) Studies on the phenology and habitat preferences of aphidophagous syrphids. (2) Studies on oviposition by syrphids on artificially infected sprouts in a variety of habitats. (3) Studies on the development of aphid populations on sprouts in the two areas. The phenological work showed that the main predator in this study, Syrphus balteatus, has only one generation each year, not several as suggested in the literature. Some syrphid species were found to be to woodland and also in an adjoining hedge. However, these woodland based species did not lay many eggs on sprouts except in the wood and in the immediate shelter of the hedge. Even 30 m from the hedge no more eggs were laid than in a site in the middle of an arable area. Neither was there any evidence that syrphid species which were more generally distributed and those which were mainly found in open habitats laid more abundantly in the area of diverse habitats than in the mainly arable area. The experimental study of aphid populations showed that syrphids reduced aphid numbers significantly only in the mainly arable area. This supports the view that the presence of rich non-crop habitats does not increase syrphid oviposition, at least on the scale of this experiment. suggested.
The faunal changes in the crown stratum of a newly established red pine plantation were observed during the first five years of growth. The crown faunae of three older stands planted in 1950, 1939, and 1929 were sampled throughout the growing seasons of four consecutive years by a technique employing pyrethrum insecticide.
The stands represent four stages in the development of a red pine community over a period of 35 years, and the presence, distribution, density, annual and seasonal fluctuations, species succession, and food relations of arthropod taxa are discussed.
Species colonizing trees in the establishment stage are largely replaced in the transition stage by a species-complex that persists throughout the succeeding monoculture and young-forest stages. Arthropod density in relation to crown size increases rapidly until the trees are about 15 years of age, and then declines. The pattern of seasonal abundance is dominated by a few species. The ratio between parasite–predator and prey species remains remarkably stable throughout the three older stages of the community.