Lu_2019_Pestic.Biochem.Physiol_160_127

Environmental xenobiotics can influence the tolerance of insects to chemical insecticides. Heavy metals are widespread distributed, can be easily bio-accumulated in plants and subsequently within phytophagous insects via the food chains. However, less attention has been paid to the effect of heavy metal exposure on their insecticide tolerance. In this study, pre-exposure of copper (Cu, 25-100mgkg(-1)) significantly enhanced the subsequent tolerance of Spodoptera litura to beta-cypermethrin, a widely used pyrethroid insecticide in crop field. Cytochrome P450 monooxygenases (CYPs) activities were cross-induced in larvae exposed to Cu and beta-cypermethrin, while the activities of glutathione S-transferase (GST) and carboxylesterase (CarE) were not affected. Application of piperonyl butoxide (PBO), a P450 synergist, effectively impaired the tolerance to beta-cypermethrin in Cu-exposed S. litura larvae with a synergistic ratio of 1.72, indicating that P450s contribute to larval tolerance to beta-cypermethrin induced by Cu exposure. Among the four CYP6AB family genes examined, only larval midgut-specific CYP6AB12 was found to be cross-induced by Cu and beta-cypermethrin. RNA interference (RNAi)-mediated silencing of CYP6AB12 effectively decreased the mRNA levels of the target gene, and significantly reduced the larval tolerance to beta-cypermethrin following exposure to Cu. These results showed that pre-exposure of heavy metal Cu enhanced larval tolerance to beta-cypermethrin in S. litura, possibly through the cross-induction of P450s. Our findings provide new insights on the relationship between heavy metals and chemical insecticides that may benefit both the risk evaluation of heavy metal contamination and development of pest management strategies.