Cnaphalocrocis medinalis is a destructive migratory rice pest. Although many studies have investigated its behavioral and physiological responses to environmental changes and migration-inducing factors, little is known about its molecular mechanisms. This study was conducted to select suitable RT-qPCR reference genes to facilitate future gene expression studies. Here, thirteen candidate housekeeping genes (EF1α, AK, EF1β, GAPDH, PGK, RPL13, RPL18, RPS3, 18S rRNA, TBP1, TBP2, ACT, and UCCR) were selected to evaluate their stabilities under different conditions using the ∆CT method; the geNorm, NormFinder, BestKeeper algorithms; and the online tool RefFinder. The results showed that the most stable reference genes were EF1β, PGK, and RPL18, related to developmental stages; RPS3 and RPL18 in larval tissues; EF1β and PGK in larvae feeding on different rice varieties; EF1α, EF1β, and PGK in larvae temperature treatments; PGK and RPL13, related to different adult ages; PGK, EF1α, and ACT, related to adult nutritional conditions; RPL18 and PGK, related to adult mating status; and, RPS3 and PGK, related to different adult take-off characteristics. Our results reveal reference genes that apply to various experimental conditions and will greatly improve the reliability of RT-qPCR analysis for the further study of gene function in this pest.

Insect tolerance to insecticides is closely related to the host plant. Migratory insects flying downwind and landing randomly may face host-plant switching after migration. However, it is not clear whether host-plant switching affects the tolerance of migratory insects to insecticides. In the present work, Cnaphalocrocis medinalis, a migratory pest destructive to rice, was studied to explore this issue. The results show that the host-plant switch reduced the susceptibility of rice and wheat larvae populations to abamectin but increased that of wheat larvae populations to chlorpyrifos, indicating that host switching resulted in different tolerance to different insecticides. Enzyme activity determination showed that, although abamectin and chlorpyrifos affect the activities of detoxification enzymes (carboxylesterase, multifunctional oxidase, and glutathione S-transferases), antioxidant enzymes (superoxide dismutase, peroxidase, and catalase), and acetylcholinesterase at sublethal dosages, the effect depends on the host plant and insecticide species. Overall, our findings show that the induction of C. medinalis by host switching affects its susceptibility and biochemical responses to abamectin and chlorpyrifos. Insecticides against C. medinalis should be used with consideration of the potential impact of host switching. Reasonable selection and usages of insecticides can help in the resistance management and control of migratory insects.

Chilo suppressalis is one of the most important rice pests worldwide, and chlorantraniliprole, abamectin, and methoxyfenozide have been widely used to control this pest in China. However, the control efficiency in the field has dramatically decreased in recent years. Therefore, assessing the impacts of different factors on C. suppressalis resistance is essential for maintaining control effectiveness and managing resistant populations. Herein, we investigated insecticide resistance and its potential influencing factors (biotic and abiotic factors) in C. suppressalis field populations, using bioassays and biochemical and molecular diagnostic approaches. The results showed that the resistance levels of most field populations of C. suppressalis have evolved to moderate-to-high levels to the tested insecticides. The toxicity correlation analysis indicated that there was a significant positive correlation between the resistance levels of abamectin and methoxyfenozide, whereas GST activity was positively correlated with abamectin and methoxyfenozide resistance in C. suppressalis. EST and P450 activities showed significantly positive correlation with the resistance of chlorantraniliprole and methoxyfenozide, while the increase in temperature enhanced EST enzyme activity and was positively correlated with the evolution of resistance to methoxyfenozide. Overall, our study provides a systematic understanding of the dynamic resistance status and its influencing factors of C. suppressalis to insecticides. These findings will help clarify the resistance levels and the influencing factors in the resistance development of C. suppressalis, providing a theoretical basis for the resistance management of this insect species.

Pomacea canaliculata is one of the most destructive threats to the safe production of rice. Molluscicides are the primary measure for controlling this pest species. Tea saponin (TS) is a plant secondary metabolite with a high snail-killing activity. However, some individuals have enhanced detoxification metabolism against TS, leading to a weakened control efficiency of TS to P. canaliculata. To clarify the detoxification and metabolic mechanisms of TS in P. canaliculata, we characterized the toxicity of TS against the snails. Additionally, we examined its biochemical and molecular effects on glutathione S-transferases (GSTs) and monoamine oxidase (MAO) activities, as well as their corresponding gene expression levels. The results showed that the LC₅₀ values were 6.12, 9.03, and 9.35 mg/L for small, medium, and large snails following 24 h exposure. The LT₅₀ values were 16.85, 20.96, and 29.85 h for small, medium, and large snails at a concentration of 9 mg/L exposure, respectively. Furthermore, as the TS concentration increased or the treatment duration was prolonged, the activities of GSTs and MAO increased, along with the corresponding gene expression levels of PcGSTs1, PcGSTo1, PcmGST1 and PcMAO, compared to those of untreated snails. These results indicated that TS displayed dose- and time-dependent toxicity to P. canaliculata. Overall, the biochemical and molecular results suggested that GSTs and MAO were probably involved in the detoxification metabolism of P. canaliculata against TS. These findings preliminarily clarified the detoxification mechanism of P. canaliculata against TS.