Helicoverpa armigera is an universal pest around the world, which has recovered again in recent years because of the adjustment of cropping structure and resistance to Bacillus thuringiensis (Bt) in China. As a new insecticide spinetoram is extensively used to control many pest insects, including H. armigera. However the lethal and sublethal effects of spinetoram on cotton bollworm have not been assessed. In the present study, the toxicity of spinetoram against cotton bollworm was tested under laboratory conditions. Results demonstrated spinetoram showed an excellent activity against H. armigera, especially, against Bt (Cry1Ac) resistant H. armigera. Treatment with spinetoram at the doses of 0.19 mg/kg and 0.36 mg/kg (LC₈ and LC₂₀ after 24h oral exposure) significantly arrested the development of surviving larvae and caused significant decrease in larvae wet weight. Besides, the survivors after spinetoram treatments showed significant reduction of pupation ratio, pupal weight, emergence ratio, longevity and fecundity of adults. At same time, spinetoram treatments resulted in significant increase in the prepupal and pupal periods of survivors. In summary, these results showed that spinetoram could be used as an effective pesticide to control H. armigera, especially Cry1Ac-ressitacne, consequently to take both lethal and sublethal effects to cotton bollworm into consideration in cotton bollworm control strategy.

Crystalline (Cry) proteins from Bacillus thuringiensis (Bt) are used extensively for insect control in sprays and transgenic plants, but their efficacy is reduced by evolution of resistance in pests. Here we evaluated reduced activation of Cry1Ac protoxin as a potential mechanism of resistance in the invasive pest Helicoverpa armigera. Based on the concentration killing 50% of larvae (LC₅₀) for a laboratory-selected resistant strain (LF120) divided by the LC₅₀ for its susceptible parent strain (LF), the resistance ratio was 1600 for Cry1Ac protoxin and 1200 for trypsin-activated Cry1Ac toxin. The high level of resistance to activated toxin as well as to protoxin indicates reduced activation of protoxin is not a major mechanism of resistance to Cry1Ac in LF120. For both insect strains, treatment with either the trypsin inhibitor N-a-tosyl-L-lysine chloromethyl ketone (TLCK) or the chymotrypsin inhibitor N-a-tosyl-L-phenylalanine chloromethyl ketone (TPCK) did not significantly affect the LC₅₀ of Cry1Ac protoxin. Enzyme activity was higher for LF than LF120 for trypsin-like proteases, but did not differ between strains for chymotrypsin-like proteases. The results here are consistent with previous reports indicating that reduced activation of protoxin is generally not a major mechanism of resistance to Bt proteins.

Helicoverpa armigera (cotton bollworm) is one of the most destructive pests worldwide. Due to resistance to Bacillus thuringiensis and conventional insecticides, an effective management strategy to control this pest is urgently needed. Spinosad, a natural pesticide, is considered an alternative; however, the mechanism underlying the developmental effects of sublethal spinosad exposure remains elusive. In this study, the mechanism was examined using an insect model of H. armigera. Results confirmed that exposure to sublethal spinosad led to reduced larval wet weight, delayed larval developmental period, caused difficulty in molting, and deformed pupae. Further investigation demonstrated that exposure to sublethal spinosad caused a significant decrease in 20E titer and increase in JH titer, thereby leading to the discordance between 20E and JH titers, and consequently alteration in the expression levels of HR3 and Kr-h1. These results suggested that sublethal spinosad caused hormonal disorders in larvae, which directly affect insect development. Our study serves as a reference and basis for the toxicity evaluation of spinosad on molting and pupation in insect metamorphosis, which may contribute to identifying targets for effective control of cotton bollworm.

Female moths use sex pheromones to attract males, and corresponding regulatory mechanism underlying sex pheromone biosynthesis is species-dependent. However, the detailed mechanism involved in sex pheromone biosynthesis in Ostrinia furnacalis has not yet been fully addressed. In the present study, transcriptome sequencing of O. furnacalis pheromone glands screened a serials of candidate genes involved in sex pheromone biosynthesis. Our analysis showed that sex pheromone release in O. furnacalis females arrives its peak at the 2^nd scotophase, consistent with its mating behavior. Pheromone biosynthesis-activating neuropeptide (PBAN) was confirmed to regulate sex pheromone biosynthesis, and Ca²⁺ is the secondary messenger of PBAN signaling in O. furnacalis. The functional analysis of candidate genes demonstrated that the decreased mRNA levels or activities of calcineurin (CaN) and acetyl-CoA carboxylase (ACC) led to significant decrease in sex pheromone production and female capability to attract males, as demonstrated by RNAi-mediated knockdown and pharmacological inhibitor assay. Most importantly, the activities of CaN and ACC depend on the activation of PBAN/PBANR/Ca²⁺. Furthermore, fatty-acyl reductase 14 was involved in PBAN-mediated sex pheromone biosynthesis. Altogether, our results demonstrated that PBAN regulates sex pheromone biosynthesis through PBANR/Ca²⁺/CaN/ACC pathway to promote sex pheromone biosynthesis in O. furnacalis and provided a reference for non-model organism to study neuropeptide signal transduction.

Supplemental nutrients of adult moths maximize moth fitness and contribute to the pollination of many plants. Previous reports have revealed that sugar feeding promotes to sex pheromone biosynthesis by increasing the haemolymph trehalose concentration in mating moths. Here, Mythimna separata adults were employed as a model to investigate the effect of sugar feeding on sex pheromone biosynthesis. Results showed that in virgin females, sugar feeding markedly increased the concentrations of trehalose, pyruvic acid, and acyl-CoA in pheromone glands (PGs), which in turn led to an increase in sex pheromone titer, female ability to attract males and successfully mating frequency in sugar-fed females. Consistently, sugar-fed females laid more eggs than water-fed females. Furthermore, the refeeding of starved females also caused significantly increase in the concentrations of trehalose, pyruvic acid, and acyl-CoA in PGs, thus facilitating a significant increase in sex pheromone production. Most importantly, RNAi-mediated knockdown of trehalase (leading to PG starvation) resulted in an increase in trehalose content, and decrease in the concentrations of pyruvic acid, and acyl-CoA in PGs, which in turn led to a decrease of sex pheromone titer, female ability to attract males and successful mating efficacy. Altogether, results revealed a mechanism by which sugar feeding contributed to trehalose utilization in PGs, promoted to significantly increased sex pheromone precursor by increasing the concentrations of pyruvic acid and acyl-CoA, and facilitated to sex pheromone biosynthesis and successful mating.