Abstract Bacterial symbionts can promote insecticide resistance in their hosts by isolating and degrading insecticidal compounds or altering the expression of host genes. Although Wolbachia, a common endosymbiont in arthropods, typically does not influence insecticide resistance, there are cases of increased or decreased susceptibility. Due to the restrictions of applying conventional insecticides in a stored product setting, studies on alternative control methods are needed, including those on entomotoxic nanoparticles and the potential for resistance. For pests of stored beans, selenium nanoparticles (SeNPs) are relatively innocuous to the azuki bean beetle, Callosobruchus chinensis (L.) (Coleoptera: Chrysomelidae: Bruchinae). Here, we hypothesized that this response is mediated by Wolbachia, and we tested this using an isofemale line of C. chinensis (infected or uninfected with Wolbachia). Our results showed that the lifespan of Wolbachia-infected females was not affected by SeNPs, but increasing concentrations of SeNPs still had a negative effect on fecundity; in uninfected females, increasing concentrations of SeNPs significantly decreased both lifespan and fecundity. However, in males, SeNPs enhanced lifespan and decreased the incidence of sexual harassment behavior regardless of infection status (for uninfected males, the duration of harassment behavior also decreased). In the presence of males, 72-h female reproduction increased independent of infection status or SeNP treatment, but egg hatchability was reduced by male presence and SeNPs. This study documents a valuable example of symbiont-mediated resistance to entomotoxic nanoparticles.
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