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Schematic representation of oviposition cups used in oviposition experiments; showing the set up with larvae (left) and chemicals (right)
Source publication
The oviposition behavior of mosquitoes is mediated by chemical cues. In the malaria mosquito Anopheles gambiae, conspecific larvae produce infochemicals that affect this behavior. Emanations from first instar larvae proved strongly attractive to gravid females, while those from fourth instars caused oviposition deterrence, suggesting that larval de...
Contexts in source publication
Context 1
... filter paper, 125 mm in diameter, Whatman® (Whatman International Ltd., Maidstone, England) was placed over the cup, serving as an oviposition site for the mosquitoes thus preventing stimulation by visual stimuli. To prevent drying out of the oviposition paper, a cylinder made of filter paper was placed in the cups (Fig. 1, left panel). This cylinder ensured that when the water level in the cup decreased, the oviposition paper remained wet. Moreover, because of the cylinder, the oviposition paper did not have to be in contact with the liquid, which would decrease the area of the water surface for the larvae to breathe. Larvae were placed within and outside of the ...
Context 2
... used in the follow-up experiments. In the second set of concentrations of DMTS (ranging from 5.5 × 10 −10 -5.5 × 10 −12 M) mosquitoes in two of the three cages did not oviposit at all. At the concentration 5.5 × 10 −11 M, oviposition bowls received fewest eggs with an OAI equal to −0.17, and this concentration was used for further experiments (Fig. ...
Citations
... Though not emitted by hosts, some VOCs have also been associated with the selection of oviposition sites by An. gambiae, An. arabiensis and Ae. aegypti gravid females [19,93,94], demonstrating that compounds produced in water bodies containing mosquito larvae may influence the selection of oviposition sites [93]. For example, dimethyl disulfide and dimethyl trisulfide detected in emanations from water containing fourth instar larvae (L4) acted as oviposition repellents, also causing retention of eggs within the gravid females [93]. ...
Volatile organic compounds (VOCs) are chemicals emitted as products of cell metabolism, which reflects the physiological and pathological conditions of any living organisms. These compounds play a key role as olfactory cues for arthropod vectors such as mosquitoes, sand flies, and ticks, which act in the transmission of pathogens to many animal species, including humans. Some VOCs may influence arthropod behaviour, e.g., host preference and oviposition site selection for gravid females. Furthermore, deadly vector-borne pathogens such as Plasmodium falciparum and Leishmania infantum are suggested to manipulate the VOCs profile of the host to make them more attractive to mosquitoes and sand fly vectors, respectively. Under the above circumstances, studies on these compounds have demonstrated their potential usefulness for investigating the behavioural response of mosquitoes, sand flies, and ticks toward their vertebrate hosts, as well as potential tools for diagnosis of vector-borne diseases (VBDs). Herein, we provide an account for scientific data available on VOCs to study the host seeking behaviour of arthropod vectors, and their usefulness as attractants, repellents, or tools for an early diagnosis of VBDs.
Graphical Abstract
... Volatiles associated with conspecific aquatic stages differentially attract mosquitoes to oviposition sites and stimulate egg laying [this study, 11,12,15,17,18,20,24,[34][35][36][37][38][39][40]. In this study, gravid Ae. aegypti were preferentially attracted to oviposit in response to the VOCs emanating from water conditioned with late-stage larvae [11,20,22], which likely signals a productive breeding site and reduced competition for resources between the existing, soon to pupate, larvae and the new generation [6,20,41,42]. ...
... Both the aquatic stage and odour release rate significantly affected the manner in which females were stimulated to oviposit in either the treated or controlled sites. Our findings indicate that gravid mosquitoes rely on the detection of aquatic stage-specific VOC blends for the identification and discrimination among potential oviposition sites to provide a reliable signal of the suitability of a potential breeding site for their offspring [24,39]. This differential preference for a specific conspecific aquatic stage, and its volatiles, may have a direct effect on the population dynamics of Ae. aegypti, and provide a potential route by which to manipulate vector behaviour. ...
... The presence of conspecific aquatic stages in a breeding site, currently or in the recent past, influences and mediates the oviposition site selection and egg-laying decision of gravid mosquitoes [this study, 11,12,15,17,18,20,24,[34][35][36][37][38][39][40]44]. The behavioural responses of gravid mosquitoes to these sites are species-and taxon-specific [34,36,38,41,44]. ...
Background
Olfaction plays an important role in the selection and assessment of oviposition sites by mosquitoes. Volatile organic compounds (VOCs) associated with potential breeding sites affect the behaviour of gravid mosquitoes, with VOCs from aquatic stages of conspecific mosquitoes influencing and regulating oviposition. The purpose of this study was to conduct a systematic analysis of the behavioural response of gravid Aedes aegypti to conspecific aquatic stage-conditioned water, to identify the associated bioactive VOCs and to determine how blends of these VOCs regulate oviposition site selection and stimulate egg-laying.
Methods
Using a multi-choice olfactory oviposition assay, controlling for other sensory modalities, the responses of individual females to water conditioned with different densities of conspecific aquatic stages were assessed. The conditioned water samples from the most preferred density of each aquatic stage were subsequently compared to each other using the same oviposition assay and analysed using an analysis of variance (ANOVA) followed by a Tukey post-hoc test. Using combined gas chromatography and electroantennographic detection or mass spectrometry, bioactive VOCs from the preferred density of each aquatic stage were identified. Synthetic blends were prepared based on the identified ratios of bioactive VOCs in the aquatic stages, and then tested to determine the oviposition choice of Ae. aegypti in a dose-dependent manner, against a solvent control, using a dual-choice assay. This dataset was analysed using nominal logistic regression followed by an odds ratio comparison.
Results
Gravid Ae. aegypti responded stage- and density-dependently to water conditioned with eggs, second- and fourth-instar larvae, and pupal exuviae, but not to water conditioned with pupae alone. Multi-choice assays demonstrated that gravid mosquitoes preferred to oviposit in water conditioned with fourth-instar larvae, over the other aquatic stage-conditioned water. Gravid Ae. aegypti were attracted, and generally stimulated, to oviposit in a dose-dependent manner to the individual identified synthetic odour blends for the different aquatic stages.
Conclusions
Intraspecific VOCs regulate oviposition site selection in Ae. aegypti in a stage- and density-dependent manner. We discuss the need for further studies to evaluate the identified synthetic blends to modulate the odour-mediated oviposition of Ae. aegypti under field conditions.
Graphical Abstract
... The effect of color on the oviposition rate of different mosquito species has been studied by several researchers worldwide (Ai-Leen and Jin Song 2000; Oliva et al. 2014;Pavlovich and Rockett 2018;Schoelitsz et al. 2020). Additionally, the increase in marginalization in cities and settlement in non-standard housing has created suitable conditions for the growth and proliferation of pathogenic vectors like mosquitoes, making it even more critical to understand the ecological characteristics of mosquito oviposition sites (Bentley and Day 1989). ...
... Ovitraps have been widely used as a valuable tool for monitoring, identifying, and controlling mosquitoes (Schoelitsz et al. 2020). Having enough information about the behavior of mosquitoes can be effective in preventing diseases that can be transmitted by them . ...
Adequate knowledge of mosquito behavior can aid in the prevention of numerous diseases that they are capable of transmitting. Therefore, a comprehensive research was designed to study the effects of color and some environmental factors on the oviposition behavior and biodiversity of mosquitoes for the first time in Iran. This study was conducted in seven different locations in Shiraz city, south of Iran. Two experimental groups were included: Group 1 received well water, and Group 2 received processed water, which were applied into 28 identical containers of different colors in each group. After oviposition, the larvae were collected and identified using taxonomic keys. A total of 1386 mosquitoes were collected, with the dominant species being Culex quinquefasciatus (65.10%). The specimens collected from processed water (84.06%) were significantly higher compared to those collected from well water (15.94%) (p=0.003). The oviposition behavior of mosquitoes in aquatic habitats was completely selective based on the amount of organic matter present. The most attractive colors for mosquito oviposition were black and blue. Fig trees showed an attractant property for the oviposition of almost all mosquitoes, while medlar trees had a deterrent effect. Among all studied species, Culex perexiguus and Culex antennatus displayed completely different behavior compared to others. In conclusion, the preferred colors for mosquito oviposition (black and blue) can be used as an oviposition stimulant for almost all species and can be incorporated as the background color of ovitraps. Furthermore , colors that exhibit repellent properties can also be used as an inexpensive and environmentally friendly behavioral control tool for painting artificial mosquito oviposition sites.
... Egg retention in mosquitoes is the process by which a gravid female withholds laying a proportion of a mature egg batch (Meola and Lea, 1972) and in anophelines has been observed in response to a range of environmental cues (Dhar et al., 1996;Harris et al., 2013;Schoelitsz et al., 2020;Mwingira et al., 2020a). To determine whether eggs were retained when only dung-infused oviposition water was presented of a single dung type, no choice assays were conducted where cow (n = 26) and chicken (n = 26) dung were assessed separately. ...
The rice agroecosystem provides suitable breeding habitat for many malaria vector species, and rice-adjacent communities are consequently exposed to a greater malaria transmission risk than non-rice-associated communities. As part of efforts to expand rice production in Africa, sustainable and climate-adapted practices such as the System of Rice Intensification (SRI) are being promoted. SRI encourages the use of organic fertilisers (OFs) such as cow and chicken dung, as opposed to inorganic industrially produced fertilisers, due to their lower resource cost, apparent benefit to the rice agroecosystem and as a means to reduce the greenhouse gas emissions associated with the production of industrial fertilisers. However, the impact of OFs on mosquito fauna is not well documented and may have knock-on consequences on malaria transmission risk. Here, we demonstrate, using dual choice egg count assays, that both cow and chicken dung modulate the oviposition behaviour of Anopheles arabiensis, a major malaria vector in Sub-Saharan Africa. A significantly reduced proportion of eggs were laid in water treated with either cow or chicken dung compared to untreated water, with higher dung concentrations resulting in further reduced proportions. When presented in competition, significantly fewer eggs were laid in water treated with chicken dung than with cow dung. Moreover, there was no evidence of egg retention in any experiment, including in no-choice experiments where only dung-containing dishes were available. These results suggest both cow and chicken dung may act as oviposition deterrents to malaria vector species and that the application of manure-based OFs in rice agriculture may modulate the oviposition behaviour of An. gambiae s.l. within agroecosystems. Quantification of the ammonia present in dung-infused water showed higher concentrations were present in the chicken dung infusion, which may be one contributing factor to the difference in observed deterrence between the two dung types. Deterrence of mosquito oviposition in OF-treated farms may potentially affect the overall production of malaria vectors within rice fields and their contribution to local malaria transmission.
... Dimethyl-disulfide (DMDS , Table 3.1) has been identified in skin (Bernier et al., 2000), human breath (Geest et al., 2016;Greenman et al., 2016;Velde et al., 2008), urine (Wahl et al., 1999;Zlatkis et al., 1973) and faeces (Costello et al., 2014;Garner et al., 2007;Moore et al., 1987;Suarez et al., 1997). This compound has also been identified in the conspecific larval conditioned water of An. gambiae (Schoelitsz et al., 2020) and An. coluzzii (Suh et al., 2016), and shown to affect oviposition of gravid females. ...
... Such a potential is testified by the various reports published over the last decade on other insects species focusing on correlating biomechanical features to predatory and feeding behaviors, as well as flight ability, and on revealing anatomical traits useful in comparative morphology and evolutionary studies. 9,11,12,[91][92][93][94][95][96] Finally, such expanded knowledge may have applied relevance to develop new strategies based on the use of chemicals reproducing the olfactory cues emitted by conspecific larvae and able to affect adult oviposition, 97,98 and to better inform larvicide application to improve mosquito control in the field. 47 ...
Autofluorescence (AF) in mosquitoes is currently poorly explored, despite its great potential as a marker of body structures and biological functions. Here, for the first time AF in larval heads of two mosquitoes of key public health importance, Aedes albopictus and Culex pipiens, is studied using fluorescence imaging and spectrofluorometry, similarly to a label-free histochemical approach. In generally conserved distribution patterns, AF shows differences between mouth brushes and antennae of the two species. The blue AF ascribable to resilin at the antennal bases, more extended in Cx. pipiens, suggests a potential need to support different antennal movements. The AF spectra larger in Cx. pipiens indicate a variability in material composition and properties likely relatable to mosquito biology, including diverse feeding and locomotion behaviours with implications for vector control.
... Despite the variety of chemical signals described in these studies, there are no data available about volatile compounds emitted from water containing immature stages of Aedes mosquitoes. The sampling of headspace from larval rearing water would be a good technique for detecting volatile cues that possibly trigger oviposition behaviour of Ae. aegypti gravid females at a wider distance, as was observed with Anopheles mosquitoes [50,51]. ...
In the fight against mosquito-borne diseases, odour-based lures targeting gravid females represent a promising alternative to conventional tools for both reducing mosquito populations and monitoring pathogen transmission. To be sustainable and effective, they are expected to use semiochemicals that act specifically against the targeted vector species. In control programmes directed against Aedes aegypti, several candidates of different origins (conspecifics, plants) have already been identified as potential oviposition attractants or repellents in laboratory experiments. However, few of these candidates have received validation in field experiments, studies depicting the active molecules and their mode of perception are still scarce, and there are several methodological challenges (i.e. lack of standardization, differences in oviposition index interpretation and use) that should be addressed to ensure a better reproducibility and accelerate the validation of candidates. In this review, we address the state of the art of the compounds identified as potential candidates for trap development against Ae. aegypti and their level of validation. We also offer a critical methodological analysis, highlight remaining gaps and research priorities, and propose a workflow to validate these candidates and to increase the panel of odours available to specifically trap Ae. aegypti.
Graphical Abstract
... Studying the chemical ecology of the egg-laying behaviour of gravid malaria vectors will increase our knowledge on the sources, role and importance of volatile organic compounds (VOCs) regulating the communications between mosquitoes and their environment and might consequently facilitate the development of novel vector control and surveillance tools [13]. A range of sources for putative, attractive or repellent, chemical oviposition cues have been implicated in the literature for malaria vector mosquitoes, including from conspecific immature stages, predators, competitors, microbes, water, soil, plants and plant-based infusions [14][15][16][17][18][19][20][21][22][23]. ...
... Productive breeding sites have been associated with species from both plant families in a number of field surveys [24,26,29,40]. In nature, plant-based chemical cues interact with many other biotic and abiotic environmental cues to help gravid malaria vectors to orient and select suitable egg-laying sites, including non-plant-based chemicals [17,18,41,92,93], light and reflection [82], contrast [94], structure including plant height [29], conspecific immature stages [16,95,96], and other macroinvertebrates [14,97]. These complex interactions will need to be taken into consideration when designing 'attract-and-kill' strategies targeting gravid vectors with odour-baited traps. ...
... Studying the chemical ecology of the egg-laying behaviour of gravid malaria vectors will increase our knowledge on the sources, role and importance of volatile organic compounds (VOCs) regulating the communications between mosquitoes and their environment and might consequently facilitate the development of novel vector control and surveillance tools [13]. A range of sources for putative, attractive or repellent, chemical oviposition cues have been implicated in the literature for malaria vector mosquitoes, including from conspecific immature stages, predators, competitors, microbes, water, soil, plants and plant-based infusions [14][15][16][17][18][19][20][21][22][23]. ...
... Productive breeding sites have been associated with species from both plant families in a number of field surveys [24,26,29,40]. In nature, plant-based chemical cues interact with many other biotic and abiotic environmental cues to help gravid malaria vectors to orient and select suitable egg-laying sites, including non-plant-based chemicals [17,18,41,92,93], light and reflection [82], contrast [94], structure including plant height [29], conspecific immature stages [16,95,96], and other macroinvertebrates [14,97]. These complex interactions will need to be taken into consideration when designing 'attract-and-kill' strategies targeting gravid vectors with odour-baited traps. ...
... Studying the chemical ecology of the egg-laying behaviour of gravid malaria vectors will increase our knowledge on the sources, role and importance of volatile organic compounds (VOCs) regulating the communications between mosquitoes and their environment and might consequently facilitate the development of novel vector control and surveillance tools [13]. A range of sources for putative, attractive or repellent, chemical oviposition cues have been implicated in the literature for malaria vector mosquitoes, including from conspecific immature stages, predators, competitors, microbes, water, soil, plants and plant-based infusions [14][15][16][17][18][19][20][21][22][23]. ...
... Productive breeding sites have been associated with species from both plant families in a number of field surveys [24,26,29,40]. In nature, plant-based chemical cues interact with many other biotic and abiotic environmental cues to help gravid malaria vectors to orient and select suitable egg-laying sites, including non-plant-based chemicals [17,18,41,92,93], light and reflection [82], contrast [94], structure including plant height [29], conspecific immature stages [16,95,96], and other macroinvertebrates [14,97]. These complex interactions will need to be taken into consideration when designing 'attract-and-kill' strategies targeting gravid vectors with odour-baited traps. ...
Background
Understanding the ecology and behaviour of disease vectors, including the olfactory cues used to orient and select hosts and egg-laying sites, are essential for the development of novel, insecticide-free control tools. Selected graminoid plants have been shown to release volatile chemicals attracting malaria vectors; however, whether the attraction is selective to individual plants or more general across genera and families is still unclear.
Methods
To contribute to the current evidence, we implemented bioassays in two-port airflow olfactometers and in large field cages with four live graminoid plant species commonly found associated with malaria vector breeding sites in western Kenya: Cyperus rotundus and C. exaltatus of the Cyperaceae family, and Panicum repens and Cynodon dactylon of the Poaceae family. Additionally, we tested one Poaceae species, Cenchrus setaceus , not usually associated with water. The volatile compounds released in the headspace of the plants were identified using gas chromatography/mass spectrometry.
Results
All five plants attracted gravid vectors, with the odds of a mosquito orienting towards the choice-chamber with the plant in an olfactometer being 2–5 times higher than when no plant was present. This attraction was maintained when tested with free-flying mosquitoes over a longer distance in large field cages, though at lower strength, with the odds of attracting a female 1.5–2.5 times higher when live plants were present than when only water was present in the trap. Cyperus rotundus, previously implicated in connection with an oviposition attractant, consistently elicited the strongest response from gravid vectors. Volatiles regularly detected were limonene, β-pinene, β-elemene and β-caryophyllene, among other common plant compounds previously described in association with odour-orientation of gravid and unfed malaria vectors.
Conclusions
The present study confirms that gravid Anopheles gambiae sensu stricto use chemical cues released from graminoid plants to orientate. These cues are released from a variety of graminoid plant species in both the Cyperaceae and Poaceae family. Given the general nature of these cues, it appears unlikely that they are exclusively used for the location of suitable oviposition sites. The utilization of these chemical cues for attract-and-kill trapping strategies must be explored under natural conditions to investigate their efficiency when in competition with complex interacting natural cues.
Graphical abstract
