Abstract
The psocid, Liposcelis bostrychophila, is a globally important storage pest that has developed resistance to many chemical grain protectants, including the organophosphate insecticide malathion, posing serious challenges to food security and sustainable pest management. Carboxylesterases (CarEs) are major detoxification enzymes involved in insecticide resistance, yet the specific roles of individual isoforms, particularly integument esterases, remain poorly understood. Here, we identified LbEST-inte17, a malathion-inducible integument esterase gene through transcriptomic analysis and qPCR. RNAi-mediated silencing of LbEST-inte17 significantly increased psocid susceptibility to malathion, suggesting its critical role in tolerance. Interestingly, unlike typical CarEs that hydrolyze insecticides, in vitro assays with recombinant LbEST-inte17 together with high-performance liquid chromatography (HPLC) analysis showed no detectable malathion metabolism. Instead, molecular docking predicted a stable interaction between LbEST-inte17 and malathion (binding energy: -5.66 kcal/mol), suggesting a sequestration-based mechanism. This non-metabolic role was further validated in vivo. Overexpression of LbEST-inte17 in transgenic Drosophila melanogaster enhanced its tolerance to malathion. Collectively, our results uncover a non-canonical function for an integument esterase in insecticide tolerance, characterized by physical sequestration rather than catalytic detoxification. These findings highlight functional diversification within the CarEs family and identify a potential target for developing resistance management strategies against stored-product pests.
