Efficacy of Biopesticides for Management of the Swede Midge (Diptera: Cecidomyiidae)

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.

Azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae by releasing cathepsin in the midgut

Azadirachtin, a botanical insecticide with high potential, has been widely used in pest control. Azadirachtin has shown strong biological activity against Bactrocera dorsalis in toxicological reports, but its mechanism remains unclear. This study finds that azadirachtin A inhibits the growth and development of Bactrocera dorsalis larvae. The larval weights and body sizes of the azadirachtin-treated group were significantly less than those of the control group in a concentration-dependent manner. Further, pathological sections revealed that azadirachtin destroyed the midgut cell structure and intestinal walls, while TUNEL staining showed that azadirachtin could induce apoptosis of midgut cells, and Western blot analysis indicated that Bcl-XL expression was inhibited and cytochrome c (CytC) released into the cytoplasm. The results also imply azadirachtin-induced structural alterations in the Bactrocera dorsalis larvae midgut by activation of apoptosis. RNA-seq analysis of midgut cells found that 482 and 708 unique genes were upregulated and downregulated, respectively. These differentially expressed genes (DEGs) were enriched in apoptotic and lysosomal signaling pathways and included 26 genes of the cathepsin family. qRT-PCR verified the expression patterns of some DEGs, indicating that Cathepsin F was upregulated by 278.47-fold and that Cathepsin L and Cathepsin D were upregulated by 28.06- and 8.97-fold, respectively. Finally, association analysis between DEGs and DEMs (differentially expressed metabolites) revealed that azadirachtin significantly reduced the digestion and absorption of carbohydrates, proteins, fats, vitamins and minerals in the midgut. In conclusion, azadirachtin induces the release of cathepsin from lysosomes, causing apoptosis in the midgut. Ultimately, this leads to reduced digestion and absorption of nutrient metabolites in the midgut and inhibition of the growth and development of Bactrocera dorsalis larvae.

Azadirachtin effects on mating success, gametic abnormalities and progeny survival in Drosophila melanogaster (Diptera)

BACKGROUND

Azadirachtin is a prominent natural pesticide and represents an alternative to conventional insecticides. It has been successfully used against insect pests. However, its effects on reproduction require further analysis. Here we investigated lethal and sublethal effects of azadirachtin, on treated adults in a model insect, Drosophila melanogaster (Meigen). Dose-mortality relationships as well as several parameters of reproduction (mating, spermatogenesis, oogenesis and fertility) were examined.

RESULTS

Neem-Azal, a commercial formulation of azadirachtin, applied topically on newly emerged adults, increased mortality with a positive dose-dependent relationship. The LD₅₀ (0.63 μg) was determined 24 h after treatment using a non-linear regression. Adults surviving this dose had a mating success that was divided by 3 and a progeny production reduced by half when males were treated, and even more when females were treated. When combining probability of survival, of mating and reduced progeny, it appeared that LD₅₀ induced a 98% reduction in reproductive rates. Reduced progeny was partially explained by the effect of adult treatment on gametes number and abnormalities. The number of cysts and the apical nuclei positions within the cysts decreased by 29.7% and 20%, respectively, in males. In females, the number of oocytes per ovary and the volume of basal oocytes also decreased by 16.1% and 32.4%, respectively.

CONCLUSION

Azadirachtin causes significant toxic effects in both sexes and decreases the fecundity and fertility of D. melanogaster. Females are more sensitive to azadirachtin. © 2017 Society of Chemical Industry.

Azadirachtin impact on mate choice, female sexual receptivity and male activity in Drosophila melanogaster (Diptera: Drosophilidae)

Azadirachtin, a neem compound (Azadirachta indica) with medical and anti-insect properties, is one the most successful botanical pesticides in agricultural use. However, its controversial impact on non-targeted species and its mechanism of action need to be clarified. In addition, Azadirachtin impact on pre- and post-mating traits remains largely undocumented. The current study examined the effects of Azadirachtin on Drosophila melanogaster as a non-target and model species. Azadirachtin was applied topically at its LD₅₀ (0.63μg) on the day of adult emergence and its effect was evaluated on several traits of reproductive behavior: mate choice, male activity, female sexual receptivity, sperm storage and female sterility. In choice and no choice conditions, only male treatment reduced mating probability. Female treatment impaired mating probability only when males had the choice. Males' mating ability may have been impaired by an effect of the treatment on their mobility. Such an effect was observed in the actimeter, which revealed that treated males were less active than untreated ones, and this effect persisted over 8days. Azadirachtin treatment had, however, no effect on the nycthemeral rhythm of those males. Even when mating occurred, Azadirachtin treatment impaired post-mating responses especially when females or both sexes were treated: remating probability increases and female fertility (presence of larvae) decreases. No impairment was observed on the efficiency of mating, evaluated by the presence of sperm in the spermatheca or the ventral receptacle. Male treatment only had no significant effect on these post-mating responses. These findings provide clear evidence that Azadirachtin alters the reproductive behavior of both sexes in D. melanogaster via mating and post-mating processes.