RNA interference-mediated knockdown of a cytochrome P450 gene enhanced the toxicity of α-cypermethrin in xanthotoxin-fed larvae of Spodoptera exigua (Hubner)

The beet armyworm (Spodoptera exigua) is a highly polyphagous agricultural pest that is distributed worldwide. However, the adaptive mechanisms of S. exigua for various insecticides and defensive substances in host plants are unknown. Insect P450 monooxygenases play an important role in the detoxification of plant toxins and insecticides, leading to insecticides resistance. We investigated the induced effects of xanthotoxin exposure on detoxification enzyme activity and larval tolerance to alpha-cypermethrin in S. exigua. Our results showed that the lethal concentration (LC50) of alpha-cypermethrin for xanthotoxin-exposed larvae was 2.1-fold higher than in the control. Moreover, cytochrome P450 enzyme activity was significantly elevated by upregulation of P450 genes in treated larvae. RT-qPCR results showed that CYP9A10 expression level was significantly increased in all treatments, while maximal expression level was observed in xanthotoxin + alpha-cypermethrin-fed larvae. RNAi-mediated silencing of CYP9A10 further increased mortality by 18%, 26% and 35% at 48 h and by 27%, 43% and 55% at 72 h when larvae were exposed to diets containing chemicals as compared to the control. The results show that CYP9A10 might play an important role in xanthotoxin and alpha-cypermethrin detoxification in S. exigua. RNAi-mediated silencing could provide an effective synergistic agent for pest control or insecticide resistance management.