Modelling the spread of a novel endosymbiont infection in field populations of an aphid pest

Endosymbiotic bacteria are being increasingly considered in novel methods of suppressing pest populations and/or reducing their potential to vector viruses. Here, we develop a generic modelling approach to explore the potential impacts of endosymbionts on pest populations. The model is presented as a modular R package, EndoSim. We use it to model demographic changes in the green peach aphid (Myzus persicae), which has recently been transinfected with the facultative endosymbiont, Rickettsiella. This novel transinfection has deleterious fitness effects following transfer to M. persicae. We consider a range of scenarios including different temperatures, thermal response curves, plant-based transmission dynamics, introduction dates and initial introduction sizes to investigate conditions under which Rickettsiella is expected to suppress M. persicae populations. We show that impacts on field pest populations are influenced by endosymbiont transmission dynamics, which are temperature-dependent, as well as aphid population processes. Our modelling approach suggests Rickettsiella could be used as a potential biological control to suppress M. persicae in natural settings. Furthermore, it highlights critical information that is required to accurately estimate the likely efficacy of novel endosymbiont transinfections in aphid pest control.