Sub-lethal insecticide stress alters epimutation rate but not genetic mutation rate in the pest insect Myzus persicae

Insect pests evolve heritable resistance to insecticides through selection acting on genetic variation generated by mutation. It has been hypothesised that exposure to low doses of pesticides may increase mutation rate in pest genomes and accelerate resistance evolution. However, the impact of pesticide-induced stress on the mutation rate of insects has never been empirically tested. Here we leverage new, high-quality genomic resources for the aphid pest Myzus persicae in conjunction with long-term mutation accumulation experiments to interrogate spontaneous genetic and epigenetic mutation rates in insecticide-exposed and unexposed aphid lines. Our data reveal that multigenerational exposure of Myzus persicae to sublethal concentrations of the neonicotinoid insecticide imidacloprid does not increase genetic mutation rate. Rather we show that imidacloprid exposure results in a significantly lower epimutation rate. These findings reveal the rate of origin and composition of (epi)mutations arising in a pest insect and challenge the proposed link between pesticide exposure and the rate of mutation.