THE EVOLUTION OF INSECTICIDE RESISTANCE IN THE PEACH-POTATO APHID, MYZUS-PERSICAE

The peach-potato aphid Myzus persicae (Sulzer) can resist a wide range of insecticides, but until recently (1990) the only mechanism identif ied was the increased production of carboxylesterases (E4 or FE4), whi ch cause enhanced degradation and sequestration of insecticidal esters . We have now identified two forms of target-site resistance involving changes in the acetylcholinesterase (AChE) and sodium channel (kdr) g enes. Biochemical and DNA diagnostic methods can be used to identify a ll three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. Amplified genes underlie the increased production of esterases, but their expression is modulat ed by DNA methylation. Amplification of the E4 gene is in strong linka ge disequilibrium with the kdr mechanism. This may reflect strong inse cticidal selection favouring aphids with multiple mechanisms, tight ch romosomal linkage and/or the prominence of parthenogenesis in many M. persicae populations. The decreased fitness of resistant aphids under winter conditions may be a consequence of the altered sodium-channel g ene affecting behaviour and/or the perception of external stimuli.