Novel transinfections of Rickettsiella across multiple clonal genotypes are compatible with chemical and entomopathogen control of Myzus persicae.

Symbiotic bacteria are of increasing interest as new, alternative biological control candidates for managing insect pests. Previous work has found that a novel, self-spreading, transinfection of the endosymbiont, Rickettsiella viridis, can induce fitness costs in the globally invasive aphid pest, Myzus persicae (Sulzer). Endosymbiont transinfections could be used in broad scale management if they do not interfere with other common control options that are compatible with integrated pest management at local scales. In this work, we studied the effect of a novel Rickettsiella transinfection on chemical and entomopathogen responses in M. persicae. Our experiments used 4 different clonal genotypes that varied in their resistance to chemical insecticides, allowing us to capture the potential genetic variability in the response of aphid hosts to the Rickettsiella infection. These aphid genotypes were exposed to 3 chemical insecticides registered for aphid control in Australian agriculture (bifenthrin, a pyrethroid; dimethoate, an organophosphate; and imidacloprid, a neonicotinoid), as well as the fungal entomopathogen, Beauveria bassiana (Balsamo). Mortality following chemical insecticide exposure varied considerably among aphid genotypes but was unaffected by the Rickettsiella infection. Mortality and fecundity following fungal entomopathogen exposure exhibited interactions between genotype and Rickettsiella infection status, with some possible transgenerational effects. However, there was no evidence that the efficacy of Beauveria was compromised by Rickettsiella. These results support the potential for the general use of Rickettsiella as a biological control agent, which could be released into natural populations as part of area-wide strategies to establish infections and suppress pest populations.