Hormetic effect induced by Beauveria bassiana in Myzus persicae

Myzus persicae, a serious sap-sucking pest of a large variety of host plants in agriculture, is traditionally controlled using chemical insecticides but there is interest in using biopesticides as restrictions are increasingly placed on the use of broad-spectrum pesticides. Here we show that in petri dish experiments high concentrations of the fungal entomopathogen Beauveria bassiana (strain PRRI 5336) lead to rapid mortality of M. persicae but at a low concentration (1 x 104 conidia mL-1) there is a hormetic effect where longevity and fecundity are enhanced. Hormetic effects persisted across a generation with reduced development times and increased fecundity in the offspring of M. persicae exposed to B. bassiana. Whole plant experiments point to a hormetic effect being detected in two out of three tested lines. The impact of these effects might also depend on whether M. persicae was transinfected with the endosymbiont Rickettsiella viridis, which decreases fecundity and survival compared to aphids lacking this endosymbiont. This fecundity cost was ameliorated in the generation following exposure to the entomopathogen. While B. bassiana is effective in controlling M. persicae especially at higher spore concentrations, utilization of this entomopathogen requires careful consideration of hormetic effects at lower spore concentrations, and further research to optimize its application for sustainable agriculture is recommended. AUTHOR SUMMARYBiopesticides such as Beauveria bassiana can be effective alternatives to chemical insecticides to control insect pests. We tested the efficacy of this biopesticide against the important agricultural pest aphid Myzus persicae in laboratory experiments. We also tested whether the potential biological control agent and endosymbiont Rickettsiella viridis could provide protection against mortality caused by B. bassiana. While high doses of B. bassiana caused rapid mortality in aphids, low doses enhanced aphid fecundity and survival. This enhancement persisted into the next generation, with shortened development times and increased fecundity regardless, even when high doses were used in the previous generation. The endosymbiont R. viridis did not provide clear protection against B. bassiana, in contrast to previous studies in other aphid species, but beneficial effects at low doses also occurred in this aphid line. We also observed hormesis on experiments on whole plants, but only for some aphid genotypes. To a lesser extent, we also observed beneficial effects of low doses of B. bassiana in experiments on whole plants, but only in some aphid genotypes. Fitness enhancement by biopesticides at low doses raises concerns for field applications but further research is required to understand its underlying mechanisms.