Abstract: 【Aim】 This study aims to address the effects of pyrethroid insecticides on the structure and metabolism of larval gut microbiota of Helicoverpa armigera and to enrich the knowledge about the action mechanisms of pesticides. 【Methods】 The 2nd and 3rd instar larvae of H. armigera were fed with the normal artificial diet (control group, SS) and diets containing 2% tefluthrin (type I pyrethroid) powder (tefluthrin treatment group, Te) and 2.5% deltamethrin (type II pyrethroid) emulsifiable concentrate (deltamethrin treatment group, DM), respectively, and then the genomic DNA of gut bacteria of the 3rd instar larvae was extracted. Then the V3-V4 region of 16S rDNA of gut bacteria was sequenced using Illumina MiSeq of the 2nd generation high-throughput sequencing technology to analyze the diversity and abundance of gut bacteria, and qPCR was performed to verify the 16S rDNA sequencing and analysis results. In addition, the gut samples of the 2nd and 3rd instar larvae of H. armigera were milled for Biolog-Eco experiment to analyze the metabolism of 31 carbon sources by gut bacteria on the Eco plate. 【Results】 Sequencing results of 16S rDNA showed that the gut bacteria of the 3rd instar larvae of H. armigera were mainly composed of Firmicutes, Proteobacteria, Bacteroidetes and Cyanobacteria. Compared with the control group, the α-diversity index of the larval gut bacteria in the deltamethrin and tefluthrin treatment groups did not change significantly, but the community structure of bacteria changed. At the phylum level, the relative abundance of Bacteroides in the deltamethrin and tefluthrin treatment groups decreased as compared with that in the control group, while that of Firmicutes and Cyanobacteria increased. qPCR verification results supported the above 16S rDNA sequencing and analysis results. At the genus level, the relative abundance of Bacteroides, Prevotella, and Pseudomonas was reduced, and that of Clostridium sensu stricto 1, Escherichia-Shigella, and Halomonas increased, especially Halomonas with significant increase. Biolog-Eco results showed that the metabolic capacity of carboxylic acid carbon sources in the 2nd instar larvae in the deltamethrin treatment group and the metabolic capacity of DL-alpha-glycerophosphate, hepatose, and L-phenylalanine in the 3rd instar larvae in the tefluthrin and deltamethrin treatment groups decreased as compared with those in the control group. 【Conclusion】 The results indicate that pyrethroid insecticides have notable effects on the structure and metabolic capacity of larval gut microbiota of H. armigera. Pyrethroid insecticides reduce the relative abundance of beneficial bacteria but increase the relative abundance of pathogenic bacteria in the gut of H. armigera. Short-term pyrethroid treatment does not result in the increased abundance of resistant bacteria. The qPCR results are similar to the 16S rDNA sequencing and analysis results. Type Ⅰ and type Ⅱ pyrethroids exhibit different effects on the structure and metabolic functions of gut bacteria of H. armigera.

Key words: Helicoverpa armigera, gut bacteria, bacterial community structure, 16S rDNA; Biolog-Eco, pyrethroids, carbon source