Li_2020_Pest.Manag.Sci_77_1936

BACKGROUND: Bacterial symbionts in insects, especially aphids, have a major influence on host adaptation. The authors previously showed that infection with the secondary symbiont Hamiltonella defensa increases the fitness of the wheat aphid Sitobion miscanthi, yielding increases in fitness parameters such as adult weight and offspring number. However, whether H. defensa affects the sensitivity of host aphids to insecticides remains unknown. RESULTS: We tested the effects of H. defensa on host aphid susceptibility to the insecticides chlorpyrifos methyl, imidacloprid, cyantraniliprole and acetamiprid. Our results showed that compared with Hamiltonella-free aphid clones, Hamiltonella-infected aphid clones exhibited lower sensitivity to most of the tested insecticides at low concentrations. Quantitative PCR showed that the density of H. defensa in the infected clones was slightly decreased at 24 h but then sharply increased until the late stage after treatment with the different insecticides. H. defensa in the host aphids was detected by fluorescence in situ hybridization and was localized to the aphid hindgut. The levels of the detoxification enzymes acetylcholinesterase (AChE), glutathione transferase (GST) and carboxylesterase (CarE) were significantly higher in the Hamiltonella-infected clones than in the Hamiltonella-free clones. CONCLUSIONS: The findings indicated that infection with H. defensa reduced aphid sensitivity to the investigated insecticides at low concentrations, potentially by increasing detoxification enzyme activity in the host. Therefore, symbiont-mediated insecticide resistance should be taken into account when performing resistance-monitoring studies. Studies of symbiont-mediated insecticide resistance may enhance our understanding of the emergence of insecticide resistance in agricultural systems. This article is protected by copyright. All rights reserved.