Identification and Functional Characterization of Nine Glutathione S-Transferase Genes in Lasioderma serricorne Reveals Their Roles in Detoxification of Emerging Fumigants

The cigarette beetle, Lasioderma serricorne, is a globally important pest of stored products, and prolonged fumigant use has accelerated resistance development. Glutathione S-transferases (GSTs) are key phase II detoxification enzymes that mediate insect tolerance to xenobiotics. In this study, we identified nine GST genes (LsGSTs) in L. serricorne and classified them into four cytosolic classes, namely epsilon, delta, theta, and sigma, based on phylogenetic analysis. Most LsGSTs were predominantly expressed during larval stages, while LsGSTs7 showed peak expression in adults. Tissue-specific profiling revealed predominant expression in metabolically active organs, including the fat body, Malpighian tubules, and midgut. Inhibition of GST activity using diethyl maleate (DEM) significantly increased larval susceptibility to three emerging fumigants: ethyl formate, benzothiazole, and methyl isothiocyanate. Exposure to LC30 and LC50 concentrations of these fumigants induced up-regulation of multiple LsGSTs, highlighting fumigant-specific detoxification responses. RNA interference targeting nine fumigant-inducible LsGSTs markedly elevated mortality and decreased total GST activity under fumigant stress. Furthermore, recombinant LsGSTs6 protein effectively metabolized methyl isothiocyanate, confirming their direct role in fumigant detoxification. Collectively, these findings provide novel insights into the molecular mechanisms underlying GST-mediated tolerance in L. serricorne and identify specific GST isoenzymes as promising molecular targets for innovative resistance management strategies in stored-product pest control.