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

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)

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.

Synthetic pheromone exposure increases calling and reduces subsequent mating in female Contarinia nasturtii (Diptera: Cecidomyiidae)

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.

Mini-review: recent advances in the identification and application of sex pheromones of gall midges (Diptera: Cecidomyiidae)

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.