| Summary: | Symbiotic bacteria and hormesis in aphids are the driving forces for pesticide resistance. However, the mechanism remains unclear. In this study, the effects of imidacloprid on the population growth parameters and symbiotic bacterial communities of three successive generations of <i>Acyrthosiphon gossypii</i> were investigated. The bioassay results showed that imidacloprid had high toxicity to <i>A. gossypii</i> with an LC<sub>50</sub> of 1.46 mg·L<sup>−1</sup>. The fecundity and longevity of the G0 generation of <i>A. gossypii</i> decreased when exposed to the LC<sub>15</sub> of imidacloprid. The net reproductive rate (<i>R</i><sub>0</sub>), intrinsic rate of increase (<i>r<sub>m</sub></i>), finite rate of increase (<i>λ</i>), and total reproductive rate (<i>GRR</i>) of G1 and G2 offspring were significantly increased, but those of the control and G3 offspring were not. In addition, sequencing data showed that the symbiotic bacteria of <i>A. gossypii</i> mainly belonged to Proteobacteria, with a relative abundance of 98.68%. The dominant genera of the symbiotic bacterial community were <i>Buchnera</i> and <i>Arsenophonus</i>. After treatment with the LC<sub>15</sub> of imidacloprid, the diversity and species number of bacterial communities of <i>A. gossypii</i> decreased for G1–G3 and the abundance of <i>Candidatus-Hamiltonella</i> decreased, but <i>Buchnera</i> increased. These results provide insight into the resistance mechanism of insecticides and the stress adaptation between symbiotic bacteria and aphids.
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