Gut Microbiota Mediate Insecticide Resistance in the Diamondback Moth, Plutella xylostella (L.)

Abstract

The development of insecticide resistance in insect pests is a worldwide concern and elucidating the underlying mechanisms is critical for effective crop protection. Recent studies have indicated potential links between insect gut microbiota and insecticide resistance and these may apply to the diamondback moth, <i>Plutella xylostella</i> (L.), a globally and economically important pest of cruciferous crops. We isolated <i>Enterococcus</i> sp. (Firmicutes), <i>Enterobacter</i> sp. (Proteobacteria), and <i>Serratia</i> sp. (Proteobacteria) from the guts of <i>P. xylostella</i> and analyzed the effects on, and underlying mechanisms of insecticide resistance. <i>Enterococcus</i> sp. enhanced resistance to the widely used insecticide, chlorpyrifos, in <i>P. xylostella</i>, while in contrast, <i>Serratia</i> sp. decreased resistance and <i>Enterobacter</i> sp. and all strains of heat-killed bacteria had no effect. Importantly, the direct degradation of chlorpyrifos <i>in vitro</i> was consistent among the three strains of bacteria. We found that <i>Enterococcus</i> sp., vitamin C, and acetylsalicylic acid enhanced insecticide resistance in <i>P. xylostella</i> and had similar effects on expression of <i>P. xylostella</i> antimicrobial peptides. Expression of cecropin was down-regulated by the two compounds, while gloverin was up-regulated. Bacteria that were not associated with insecticide resistance induced contrasting gene expression profiles to <i>Enterococcus</i> sp. and the compounds. Our studies confirmed that gut bacteria play an important role in <i>P. xylostella</i> insecticide resistance, but the main mechanism is not direct detoxification of insecticides by gut bacteria. We also suggest that the influence of gut bacteria on insecticide resistance may depend on effects on the immune system. Our work advances understanding of the evolution of insecticide resistance in this key pest and highlights directions for research into insecticide resistance in other insect pest species.