Gut bacteria of the fall armyworm, Spodoptera frugiperda, promote host resistance against the toxic effects of lufenuron

Abstract

The fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is a highly polyphagous agricultural pest that seriously threatens food production and agricultural development. Lufenuron is widely used because of its good control effect and safety to nontarget organisms. However, due to the continuous application of lufenuron and the evolution of insect resistance mechanisms, the potential of S. frugiperda developing resistance to lufenuron is increasing. Insect gut bacteria play an important role in insecticide resistance. We established a germ-free (GF) rearing protocol and cultured monoassociated gnotobiotic S. frugiperda with 20 different bacteria to explore the possible mechanisms of gut bacteria resistance in insects. After the larvae were exposed to lufenuron, Klebsiella C3 was screened, which could significantly change the resistance of larvae to lufenuron. Moreover, chitin synthesis and metabolism in larvae fed with Klebsiella C3 were significantly affected. The liquid chromatography results showed that Klebsiella C3 could not directly degrade lufenuron. Nontargeted metabolomics analysis revealed that the intervention of Klebsiella C3 resulted in the production of different metabolites by S. frugiperda, which affected the associated metabolic pathways. These changes in substances may be responsible for the altered sensitivity of S. frugiperda to lufenuron. Taken together, our study investigated how intestinal bacteria influence the resistance of S. frugiperda against insecticides. This research offers new insights for developing preventive and control strategies against this key pest.