Lead exposure improves the tolerance of Spodoptera litura (Lepidoptera: Noctuidae) to cypermethrin

► First study the relationship between Pb exposure and insect tolerance to cypermethrin. ► Short-term or long-term lead exposure can improve larvae tolerance to cypermethrin. ► Pb accumulations were detected in midgut, fat body, brain and hemolymph. ► Expression of P450s in midgut and fat body of Spodoptera litura enhanced after Pb exposure. Many ecological factors such as heavy metals can affect the tolerance of herbivorous insects to chemical insecticide. Spodoptera litura larvae exposed to lead (Pb) (0–100mgkg−1 in artificial diet) did not inhibit their growth. After 96h of Pb (0–100mgkg−1) exposure, topical application and feeding of cypermethrin to S. litura decreased their mortality and increased weight gain. Moreover, the mortality of S. litura treated with 25 and 50mgkg−1 of Pb for five generations was significantly lower than control. In addition, Pb accumulation was detected in midgut, fat body, brain and hemolymph, and its highest level was in the midgut. Furthermore, there was a significant negative correlation between Pb accumulation in fat body and mortality after topical application of cypermethrin. After 96h of Pb exposure, there was increase expression of detoxification enzymes (CYP9A39 and CYP6B47) in midgut and fat body of S. litura. Therefore, the tolerance of S. litura to cypermethrin is increased by Pb exposure at certain concentrations through Pb accumulation in body and the increase of CYP9A39 and CYP6B47 expression.