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Racemic Pheromone Blends Disrupt Mate Location in the Invasive Swede Midge, Contarinia nasturtii

Authors:
Elisabeth Hodgdon at Cornell University
Elisabeth Hodgdon
Rebecca H Hallett at University of Guelph
Rebecca H Hallett
Kimberly F. Wallin
Kimberly F. Wallin
Kimberly F. Wallin
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Chase Stratton at Delaware State University
Chase Stratton
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Abstract and Figures

Swede midge, Contarinia nasturtii Kieffer, is an invasive cecidomyiid pest that causes serious losses of Brassica oilseed and vegetable crops in the Northeastern U.S. and Canada. Currently, few alternatives to systemic insecticides exist for its management. Because a single feeding larva can render heading Brassica crops unmarketable, management strategies that prevent oviposition are needed urgently. Pheromone-mediated mating disruption is a promising management approach for swede midge because it prevents mating and subsequent crop damage. While the swede midge pheromone has been identified, one of the major barriers to using it in mating disruption is the high cost of synthesis. Racemic blends, consisting of natural and non-natural stereoisomers, could be useful for mating disruption because they are cheaper to produce. However, it is not clear whether racemic pheromone blends attract males and/or prevent them from locating and mating with females. Here, we studied the behavior of male swede midge in Y-tube and wind tunnel bioassays to pheromone blends. Specifically, we tested whether males: (1) are attracted to different doses of pheromone, (2) discriminate between blends comprising natural stereospecific or racemic components, or a combination thereof, and (3) are able to locate and copulate with females in pheromone-permeated olfactometers. We found that picogram amounts of pheromone attracted males and prevented them from locating females in y-tube olfactometers. While males were more attracted to stereospecific blends, compared to racemic blends, all blends tested prevented nearly all males mating with females. Therefore, low dose racemic blends may be promising for pheromone-mediated mating disruption.
Percentage of male swede midges (n = 40) flying to the pheromone source in a y-tube olfactometer. Pheromone concentrations are displayed in amounts of (2S, 10S)-diacetoxyundecane, the main component in the swede midge pheromone blend, with (2S, 9S)-diacetoxyundecane and (S)-2-acetoxyundecane following in the ratio produced by females (2:1:0.02, respectively) (Hillbur et al. 2005). Connecting lines offer visual guidance between data points rather than interconnectedness of data. The 0.0040 ng dose of (2S, 10S)-diacetoxyundecane was the only treatment that attracted numbers of midges greater than 50% (P = 0.017)
Percentage of male swede midges (n = 40) flying to the pheromone source in a y-tube olfactometer. Pheromone concentrations are displayed in amounts of (2S, 10S)-diacetoxyundecane, the main component in the swede midge pheromone blend, with (2S, 9S)-diacetoxyundecane and (S)-2-acetoxyundecane following in the ratio produced by females (2:1:0.02, respectively) (Hillbur et al. 2005). Connecting lines offer visual guidance between data points rather than interconnectedness of data. The 0.0040 ng dose of (2S, 10S)-diacetoxyundecane was the only treatment that attracted numbers of midges greater than 50% (P = 0.017)
… 
Y-tube for swede midge pheromone-mediated mating disruption experiment (not to scale). Air entered each arm of the y-tube via Teflon tubing (a) from an air compressor and carbon filters (not shown). Air passed through odor adaptors (b) containing filter paper with pheromone treatments (Table 2), in which each arm received the same pheromone treatment. Five live females loaded into one arm (c) were exposed to the male released into the stem of the y-tube (d). The remaining arm (e) contained no females
Y-tube for swede midge pheromone-mediated mating disruption experiment (not to scale). Air entered each arm of the y-tube via Teflon tubing (a) from an air compressor and carbon filters (not shown). Air passed through odor adaptors (b) containing filter paper with pheromone treatments (Table 2), in which each arm received the same pheromone treatment. Five live females loaded into one arm (c) were exposed to the male released into the stem of the y-tube (d). The remaining arm (e) contained no females
… 
Percentage of male swede midges (n = 70 each treatment) choosing pheromone blends (Table 2; where Ss = stereospecific and Rac = racemic) when given a choice between two blends in the y-tube olfactometer. NS, **, and *** indicate non-significance (P > 0.05), and statistical significance at P < 0.01 and P < 0.001, respectively, for individual pairwise pheromone comparisons
Percentage of male swede midges (n = 70 each treatment) choosing pheromone blends (Table 2; where Ss = stereospecific and Rac = racemic) when given a choice between two blends in the y-tube olfactometer. NS, **, and *** indicate non-significance (P > 0.05), and statistical significance at P < 0.01 and P < 0.001, respectively, for individual pairwise pheromone comparisons
… 
Percentage of male swede midges (n = 50) landing within 60 cm, 5 cm, and making contact with the pheromone source (Table 2; where Ss = stereospecific and Rac = racemic) in the wind tunnel. Connecting lines offer visual guidance between data points rather than interconnectedness of data. Data points with the same letter at the same landing distance are not different based on chi square post hoc tests (P > 0.05); *** indicates significance of the overall model at each distance at P < 0.001
Percentage of male swede midges (n = 50) landing within 60 cm, 5 cm, and making contact with the pheromone source (Table 2; where Ss = stereospecific and Rac = racemic) in the wind tunnel. Connecting lines offer visual guidance between data points rather than interconnectedness of data. Data points with the same letter at the same landing distance are not different based on chi square post hoc tests (P > 0.05); *** indicates significance of the overall model at each distance at P < 0.001
… 
Percentage of male swede midges (n = 50 for each treatment) fanning wings after landing in response to pheromone blends (Table 2; where Ss = stereospecific and Rac = racemic) in a wind tunnel. Treatments with the same letter are not different (P > 0.05) based on post hoc chi square tests; *** indicates statistical significance of the overall model at P < 0.001
+1
Percentage of male swede midges (n = 50 for each treatment) fanning wings after landing in response to pheromone blends (Table 2; where Ss = stereospecific and Rac = racemic) in a wind tunnel. Treatments with the same letter are not different (P > 0.05) based on post hoc chi square tests; *** indicates statistical significance of the overall model at P < 0.001
… 
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Racemic Pheromone Blends Disrupt Mate Location in the Invasive
Swede Midge, Contarinia nasturtii
Elisabeth A. Hodgdon
1
&Rebecca H. Hallett
2
&Kimberly F. Wallin
3,4
&Chase A. Stratton
1
&Yolanda H. Chen
1
Received: 5 February 2019 /Revised: 4 May 2019 /Accepted: 28 May 2019 /Published online: 22 June 2019
#Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
Swede midge, Contarinia nasturtii Kieffer, is an invasive cecidomyiid pest that causes serious losses of Brassica oilseed and
vegetable crops in the Northeastern U.S. and Canada. Currently, few alternatives to systemic insecticides exist for its manage-
ment. Because a single feeding larva can render heading Brassica crops unmarketable, management strategies that prevent
oviposition are needed urgently. Pheromone-mediated mating disruption is a promising management approach for swede midge
because it prevents mating and subsequent crop damage.While the swede midge pheromone has been identified, one of the major
barriers to using it in mating disruption is the high cost of synthesis. Racemic blends, consisting of natural and non-natural
stereoisomers, could be useful for mating disruption because they are cheaper to produce. However, it is not clear whether
racemic pheromone blends attract males and/or prevent them from locating and mating with females. Here, we studied the
behavior of male swede midge in Y-tube and wind tunnel bioassays to pheromone blends. Specifically, we tested whether males:
(1) are attracted to different doses of pheromone, (2) discriminate between blends comprising natural stereospecific or racemic
components, or a combination thereof, and (3) are able to locate and copulate with females in pheromone-permeated olfactom-
eters. We found that picogram amounts of pheromone attracted males and prevented them from locating females in y-tube
olfactometers. While males were more attracted to stereospecific blends, compared to racemic blends, all blends tested prevented
nearly all males mating with females. Therefore, low dose racemic blends may be promising for pheromone-mediated mating
disruption.
Keywords Pheromone .Mating disruption .Vegetable pest management .Reproduction .Swede midge .Cecidomyiidae
Introduction
Contarinia nasturtii Kieffer (swede midge; Diptera:
Cecidomyiidae) is a small galling fly that is a serious pest of
Brassica spp. (Brassicaceae) vegetable and oilseed crops in
Europe, Eastern Canada and the Northeastern USA (Chen et al.
2011; Hallett and Heal 2001). Larvae feed within the plant mer-
istem, causing deformed and scarred leaves and stems and, in
severe cases, can cause complete loss of heads of broccoli, cau-
liflower, cabbage, and other related Brassica crops. Recently,
vegetable growers in the US states of New York and Vermont
reported up to 100% yield loss of organic kale and broccoli (Y.
Chen, C. Hoepting, pers. comm.). No insecticides that are ap-
proved for certified-organic production are effective in control-
ling the midge (Evans and Hallett 2016;Seamanetal.2014).
Due to the severe economic losses inflicted by this pest, some
small, diversified organic growers in the region now avoid
Brassica production entirely (Y. Chen, pers. obs.).
Several aspects of swede midge biology create difficulty man-
aging this pest. The presence of multiple overlapping generations
and prolonged crop susceptibility to damage necessitates protec-
tion throughout the growing season (Hallett et al. 2009; Stratton
et al. 2018). Further, larvae are protected from foliar insecticides
within the meristem (Wu et al. 2006). Compounding these chal-
lenges is an extremely low damage threshold for vegetables. For
example, Stratton et al. (2018) found that a single larva can
render a cauliflower plant unmarketable. While some growers
use calendar sprays of conventional insecticides to manage
*Elisabeth A. Hodgdon
elisabeth.hodgdon@gmail.com
1
Department of Plant and Soil Science, University of Vermont, 63
Carrigan Dr., Burlington, VT 05405, USA
2
School of Environmental Sciences, University of Guelph, 50 Stone
Rd. East, Guelph, Ontario N1G 2W1, Canada
3
Rubenstein School of Environment and Natural Resources, 81
Carrigan Dr., Burlington, VT 05405, USA
4
United States Department of Agriculture Forest Service, Northern
Research Station, 707 Spear St., South Burlington, VT 05403, USA
Journal of Chemical Ecology (2019) 45:549–558
https://doi.org/10.1007/s10886-019-01078-0
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... mixture of (2S,9S)-diacetoxyundecane, (2S,10S)-diacetoxyundecane, and (S)-2-acetoxyundecane, 43,44 successfully disrupted male behavior and reduced midge damage to Brassica vegetable crops in European and North American studies. 43,45 Mating disruption may not be economically feasible at a commercial scale, however, due to the structural complexity (chirality) and high cost of swede midge pheromone synthesis. 43,44 To reduce the costs of pheromone inputs in a swede midge mating disruption system, racemic blends containing non-natural stereoisomers, as well as single-component pheromones, present opportunities for cost reduction by simplifying the chemical synthesis required (C. ...
... Although complete racemic blends and single components are unattractive to male swede midges, 46,47 they can disorient males and prevent mating. 45,47 Therefore, understanding how females respond to blends deviating from their natural three-component mixture may help inform pheromone blend selection in future mating disruption systems. ...
... italica)at the University of Guelph Elora Research Station in Ariss, Ontario, Canada. As part of a separate study, 45 Each plot contained 80 mating disruption dispensers, spaced in a 2 × 2 m grid pattern hanging from wire stakes 25 cm from the ground. We used reservoir-type semipermeable polyethylene bag dispensers (ChemTica Internacional S.A., Heredia, Costa Rica). ...
Synthetic pheromone exposure increases calling and reduces subsequent mating in female Contarinia nasturtii (Diptera: Cecidomyiidae)
Article
Full-text available
BACKGROUND Pheromone‐mediated mating disruption, which uses large amounts of synthetic female pheromones to interrupt insect reproductive behavior, has been successful for managing important agricultural pests. While multiple mechanisms have been discovered explaining how synthetic pheromone treatments prevent males from finding females, it is less clear how unnaturally large doses of synthetic sex pheromone impact the behavior of female insects, particularly nonlepidopteran females. In some species, ‘autodetecting’ females possess pheromone receptors and respond to ambient pheromones by altering their mating behavior. Here, we test whether exposure to stereospecific and racemic synthetic pheromones influences calling and subsequent propensity to mate in female swede midge (Contarinia nasturtii Kieffer; Diptera: Cecidomyiidae), a pest of Brassica crops. RESULTS In both laboratory and field settings, females exposed to stereospecific and racemic three‐component pheromone blends called significantly more frequently and for longer durations than midges in control treatments. In the field, midges were twice as likely to call in pheromone‐treated plots versus nontreated plots. Additionally, pheromone pre‐exposure reduced subsequent mating: while 68% of female midges mated following control conditions, only 42% and 35% of females pre‐exposed to stereospecific and racemic three‐component blends mated, respectively. CONCLUSION While more frequent calling within pheromone‐treated backgrounds may increase the likelihood that females are detected by males, a reduction in female propensity to mate would increase the efficacy of a pheromone‐mediated mating disruption system. Our work presents the first known investigation of autodetection behavior in Cecidomyiidae. Additional research is necessary to understand the implications of female autodetection for swede midge management.
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... Racemic pheromone compounds, or mixtures of all possible stereoisomers of the pheromone compounds, are typically less costly to produce and may present a more economical mating disruption system for swede midge. Although unnatural stereoisomers of the "main" (most abundant) swede midge pheromone component in the blend, (2S,10S)-diacetoxyundecane, inhibit male attraction (Boddum et al. 2009;Hodgdon et al. 2019a), they may still be useful for mating disruption. Unattractive compounds may camouflage calling females, adulterate attractive pheromone plumes, desensitise males, and otherwise prevent males from locating females (Miller et al. 2006;Miller and Gut 2015). ...
... Unattractive compounds may camouflage calling females, adulterate attractive pheromone plumes, desensitise males, and otherwise prevent males from locating females (Miller et al. 2006;Miller and Gut 2015). We previously found that racemic pheromone blends prevented male midges from mating with calling females in a mating disruption simulation trial in the laboratory (Hodgdon et al. 2019a). ...
Field tests of candidate pheromone blends show promise for mating disruption of the invasive swede midge (Diptera: Cecidomyiidae)
Article
Full-text available
  • Aug 2022
Swede midge, Contarinia nasturtii (Kieffer) (Diptera: Cecidomyiidae), causes severe economic losses in Brassica Linnaeus (Brassicaceae) crops in its invasive range in North America. Larvae feed within the meristem of their host plants, causing deformed heads, stems, and leaves. Pheromone-mediated mating disruption is particularly promising for swede midge management in high-value vegetable crops because its use is allowed in organic production. However, a major challenge to developing economically viable mating disruption is that the stereospecific three-component swede midge pheromone is costly to synthesise. In broccoli ( Brassica oleracea Linnaeus var. italica ) field plots, we tested whether stereospecific, lower-cost racemic, and single-component pheromone blends resulted in trap shutdown and reduced crop damage compared to nontreated controls. We found a significant reduction in males caught in three-component stereospecific and racemic pheromone–treated plots but not in the single-component treatments. Although marketable broccoli yields were not higher overall in the pheromone-treated plots compared with those in the controls, yields were significantly higher in the three-component stereospecific treatment in year 2. Therefore, the three-component stereospecific blend shows promise as a pheromone blend for swede midge mating disruption. However, due to high cost and levels of crop damage across all treatments, additional research is necessary to optimise swede midge mating disruption.
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... There are currently no swede midge-resistant crop varieties, although variation in swede midge crop preference has been observed on farms (Hoepting and Vande Brake 2020). Growers expressed an interest in mating disruption, a strategy currently in the research and development phase that may become commercially viable in the future (Hodgdon 2019). Growers ranked intercropping, trap cropping, and ground barriers the lowest. ...
Farm-level Losses and Grower Willingness to Try Management Strategies for Swede Midge in Vegetable Crops
Article
Full-text available
  • Oct 2022
Since its introduction to North America in the 1990s, the invasive swede midge ( Contarinia nasturtii ) has become an important pest of cruciferous (Brassicaceae) vegetables in the northeast and Great Lakes regions of the United States and the Canadian provinces of Québec and Ontario. Swede midge reduces yield in cruciferous vegetables through larval feeding that distorts growth. Overlapping generations, cryptic larval feeding, and lack of effective biopesticides pose challenges for managing swede midge effectively using current tools. In 2018, we distributed an online survey for commercial vegetable growers in the United States and Canada to measure farm-level economic impacts of swede midge and grower perspectives on new management strategies for this pest. Growers reported losing $3808 US ($4890 Canadian) on average per acre per year due to swede midge–related vegetable crop losses. Both organic and conventional growers expressed an interest in paying more for nonchemical swede midge management vs. insecticides and were interested in trying new management strategies, particularly biological control.
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... The stereospecific sex pheromone (4a) at 0.5 mg per septum exhibited more effective attractiveness to OWBMs in comparison with the 0.5 mg racemic sex pheromone (4b). This result is consistent with the findings of Hodgdon et al. 36 Thus, the reported sex pheromones had distinct attractiveness on OWBMs. The pheromones synthesized via the modular synthesis were biologically active and can be used in the management and control of gall midges. ...
Modular synthesis of the pheromone (2S,7S)‐2,7‐nonanediyl dibutyrate and its racemate and their field efficacy to control orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae)
Article
Full-text available
BACKGROUND Sudden outbreaks of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) cause huge wheat yield losses. Use of sex pheromones is more efficient than laborious egg counting to monitor these hidden‐concealed insects. Quick synthesis of the sex pheromones is therefore required to meet the sudden outbreak needs. RESULTS A synthetic approach of stereospecific and racemic S. mosellana pheromones was presented. This method afforded the stereospecific and racemic S. mosellana pheromones in three steps and high enantioselectivity (> 98% ee for (2S,7S)‐2,7‐nonanediyl dibutyrate) in less than 1 day with 74% and 73% overall yields, respectively, whereas most conventional methods require longer synthesis time with less than 40% yield. The synthesis routes could quickly and economically afford the pheromones, starting from synthon (S)‐but‐3‐yn‐2‐ol (1a) or but‐3‐yn‐2‐ol (1b), through the same three‐step processes of coupling, reduction, and esterification. The Y‐tube olfactometer results showed significant attractiveness of the synthetic stereospecific and racemic sex pheromones to S. mosellana males relative to the blank control (P < 0.001). Field trials also demonstrated significant attractiveness of the synthetic stereospecific and racemic sex pheromones relative to the blank control (P < 0.001). CONCLUSION This modular approach is conducive to the deployment of field traps and timely responses to S. mosellana outbreaks and can be a time‐saving and cost‐effective tool to manage S. mosellana. © 2022 Society of Chemical Industry.
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... Therefore, turning off the dispensers during mid-day and night-time hours could reduce the pheromone consumption and associated costs in a mating disruption system. 23 The sex pheromone emitted from apple leaf midge females (Table S2, entry 6) was identified as (13R,8Z)-13-acetoxy-8-heptadecen-2-one. 24 Boundary traps baited with a rubber septum dispenser containing 2 mg (13R,8Z)-13-acetoxy-8-heptadecen-2one were very effective at preventing midges from moving into mass-trapped plots. ...
Mini‐review: recent advances in the identification and application of sex pheromones of gall midges (Diptera: Cecidomyiidae)
Article
Full-text available
Most gall midges (Diptera: Cecidomyiidae) are cryptic agricultural pests. These tiny insects are prone to lurk in cargoes and spread over long distances. Their larvae feed in plant tissues, so their infestations are imperceptible until crop damage and economic loss appear. The application of sex pheromones is an efficient method with which to monitor and manage gall midges. The present review focuses on recent advances in the accurate identification of gall midge sex pheromones based on rapidly evolving analytical techniques and their use in field trials in integrated pest management. To date, sex pheromones from 19 species of gall midges have been identified and reported, and sex pheromone‐based monitoring systems have been developed and commercialized for at least ten gall midge species. All monitoring systems were tested in various experiments with a modicum of success. In addition to further studies of sex pheromones, identification of plant‐derived volatiles may offer potentials for the manipulation of behavioral response of gall midges, which can be used in dispensers for surveillance and control purposes. © 2020 Society of Chemical Industry
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A Single Swede Midge (Diptera: Cecidomyiidae) Larva Can Render Cauliflower Unmarketable
Article
Full-text available
  • May 2018
  • J INSECT SCI
Swede midge, Contarinia nasturtii Kieffer (Diptera: Cecidomyiidae), is an invasive pest causing significant damage on Brassica crops in the Northeastern United States and Eastern Canada. Heading brassicas, like cauliflower, appear to be particularly susceptible. Swede midge is difficult to control because larvae feed concealed inside meristematic tissues of the plant. In order to develop damage and marketability thresholds necessary for integrated pest management, it is important to determine how many larvae render plants unmarketable and whether the timing of infestation affects the severity of damage. We manipulated larval density (0, 1, 3, 5, 10, or 20) per plant and the timing of infestation (30, 55, and 80 d after seeding) on cauliflower in the lab and field to answer the following questions: 1) What is the swede midge damage threshold? 2) How many swede midge larvae can render cauliflower crowns unmarketable? and 3) Does the age of cauliflower at infestation influence the severity of damage and marketability? We found that even a single larva can cause mild twisting and scarring in the crown rendering cauliflower unmarketable 52% of the time, with more larvae causing more severe damage and additional losses, regardless of cauliflower age at infestation.
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Efficacy of Biopesticides for Management of the Swede Midge (Diptera: Cecidomyiidae)
Article
Full-text available
  • Aug 2016
  • J ECON ENTOMOL
Management of the swede midge, Contarinia nasturtii Kieffer, in North American crucifer production relies on crop rotation and the timely application of synthetic insecticides, based on pheromone trap monitoring of local adult populations. Organically acceptable formulations of azadirachtin, pyrethrin, and spinosad, and a commercial biopesticide containing the entomopathogenic fungus, Beauveria bassiana, were evaluated for their effects on larval mortality and oviposition deterrence in the greenhouse, and on damage symptoms in the field. In greenhouse trials, pyrethrin and spinosad treatments applied up to 24 h prior to C. nasturtii exposure resulted in significant reductions in oviposition on host plants, whereas azadirachtin and B. bassiana only deterred oviposition when applied 2 h prior to exposure. Spinosad caused the highest larval reduction (∼96%) on cauliflower meristems, while azadirachtin, B. bassiana, and pyrethrin caused significant larval reduction when applied preoviposition and significant mortality when applied postoviposition. Field trials conducted with these insecticides on broccoli in 2011 produced no significant reductions in overall damage levels; however, B. bassiana treatments produced more marketable plants than did the control. In 2013, all treatments significantly reduced overall damage levels and all treatments, except B. bassiana, produced more uninfested and marketable plants than the control. Field applications of these alternative insecticides may be effective in protecting yields of broccoli and cauliflower, when combined with other tactics in an integrated pest management program.
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Mating disruption for control of the white grub beetle Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) with synthetic sex pheromone in sugarcane fields
Article
Full-text available
  • Nov 2013
The feasibility of mating disruption with synthetic sex pheromone for the control of the white grub beetle Dasylepida ishigakiensis (Coleoptera: Scarabaeidae) was examined by permeating sugarcane fields with a racemic mixture of 2-butanol (rac-2B) released from polyethylene-tube dispensers on Miyako Island, Japan in 2011. An application of rac-2B released from 10,000 tube dispensers into 3,200 m2 sugarcane fields significantly reduced the mating rate of feral females and catches of feral males with R2B-baited traps compared with the results from untreated sugarcane fields. The larval density for the treated fields was found to be nearly zero in the following winter when the corresponding figure for untreated fields was high (1.73 and 2.33/40 × 40 cm quadrat). These results clearly show that the mating disruption technique using rac-2B could be highly promising for the control of D. ishigakiensis in sugarcane fields.
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Diel patterns of emergence and reproductive behaviour in the invasive swede midge (Diptera: Cecidomyiidae)
Article
  • Jun 2019
Swede midge ( Contarinia nasturtii (Kieffer); Diptera: Cecidomyiidae) is a serious invasive pest of Brassica Linnaeus (Brassicaceae) oilseed and vegetable crops in Canada and the United States of America. Pheromone mating disruption is a promising new tactic for managing this difficult pest, but research is needed to determine how pheromone delivery can be optimised. With an understanding of swede midge diel mating patterns, pest managers could limit pheromone release to periods when midges are sexually active. We conducted a series of 24-hour trials to test whether swede midge exhibit diel periodicity of emergence, female calling, and male capture in pheromone traps. We found that females began releasing pheromones almost immediately following emergence within the first five hours after dawn. In the field, we found that males were most active from dawn until late morning, indicating that midges mate primarily during the first five hours of photophase. Low levels of reproductive activity during midday and nighttime hours present opportunities to turn off dispensers and reduce the cost of pheromone inputs in a swede midge mating disruption system.
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Mating Disruption for the 21st Century: Matching Technology With Mechanism
Article
  • Jun 2015
  • ENVIRON ENTOMOL
Progress toward proof of the principal cause of insect mating disruption under a particular set of conditions has been hindered by a lack of logical rigor and clean falsifications of possible explanations. Here we make the case that understanding of mating disruption and optimization of particular formulations can be significantly advanced by rigorous application of the principles of strong inference. To that end, we offer a dichotomous key for eight distinct categories of mating disruption and detail criteria and methodologies for differentiating among them. Mechanisms of mating disruption closely align with those established for enzyme inhibition, falling into two major categories-competitive and noncompetitive. Under competitive disruption, no impairments are experienced by males, females, or the signal of females. Therefore, males can respond to females and traps. Competitive disruption is entirely a numbers game where the ratio of dispensers to females and traps is highly consequential and renders the control pest-density-dependent. Under noncompetitive disruption, males, females, or the signal from females are already impaired when sexual activity commences. The control achieved noncompetitively offers the notable advantage of being pest-density-independent. Dosage-response curves are the best way to distinguish competitive from noncompetitive disruption. Purely competitive disruption produces: a smoothly concave curve when untransformed capture data are plotted on the y-axis against density of dispensers on the x-axis; a straight line with positive slope when the inverse of catch is plotted against density of pheromone dispensers; and, a straight line with negative slope when catch is plotted against density of pheromone dispensers × catch. Disruption operating only noncompetitively produces: a straight line with negative slope when untransformed capture data are plotted on the y-axis against density of dispensers on the x-axis; an upturning curve when the inverse of catch is plotted against density of pheromone dispensers; and, a recurving plot when catch is plotted against density of pheromone dispensers x catch. Hybrid profiles are possible when some males within the population begin the activity period already incapacitated, while those not preexposed have the capacity to respond either to traps or pheromone dispensers. Competitive mechanisms include competitive attraction, induced allopatry, and induced arrestment. Noncompetitive mechanisms include desensitization and inhibition, induced allochrony, suppressed calling and mating, camouflage, and sensory imbalance. Examples of the various disruption types within the two major categories and suggested tactics for differentiating among them are offered as seven case studies of the disruption of important pest species using various formulations are analyzed in depth. We point out how economic optimizations may be achieved once the principal and contributory causes of disruption are proven. Hopefully, these insights will pave the way to a broader and more reliable usage of this environmentally friendly pest management tactic. © The Authors 2015. Published by Oxford University Press on behalf of Entomological Society of America. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
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Genetics of Sex Determination in the Hessian Fly, Mayetiola destructor
Article
  • Jan 1991
  • J HERED
Individual females of the Hessian fly, Mayetiola destructor (Say), produce four types of progenies: (1) all female progenies, (2) all male progenies, (3) predominantly female, bisexual progenies, and (4) predominantly male, bisexual progenies. Based on experimental results, a genetic model involving a single maternal-effect, autosomal gene ( Chromosome maintenance, Cm ) was constructed to explain the occurrence of the four progeny types. Selection for lines of Hessian flies that were either monogenous or bisexual indicated that these characteristics were heritable. Matings between females and exceptional males within the monogenous line indicated that the type of progeny produced depends on maternal genotype and that exceptional individuals result from sex-chromosome nondisjunction during oogenesis. Reciprocal matings between the monogenous and bisexual lines indicated that alleles responsible for sex-chromosome maintenance segregate in a simple Mendelian fashion and have primarily a maternal effect. The genetic model proposes that sex is determined by a ratio between sex chromosomes and autosomes that is established during embryogenesis by the maintenance or elimination of the paternally derived sex chromosomes. This behavior is conditioned by three types of alleles operating at the Cm locus.
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Cabbage seedpod weevil (Coleoptera: Curculionidae): new pest of canola in northeastern North America
Article
  • Sep 2001
  • CAN ENTOMOL
In 1996, damage symptoms typical of the swede midge, Contarinia nasturtii (Keiffer), were observed on broccoli, Brassica oleracea L. var. italica (Brassicaceae), crops east of Toronto, Ontario. Early attempts to identify an associated insect larva were unsuccessful, and damage symptoms became mistakenly attributed to nutrient deficiencies (T Clarke, personal communication). Between 1996 and 1999, damaged plants were seen by growers regularly, and resulted in up to 85% loss of marketable yield (T Clarke, personal communication). In June 2000, we initiated investigations at two sites 12 km apart to determine the causal organism of this damage. Both sites were located at farms where cole crops are primarily -gown and from where the first damage reports originated.
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