Use of biochemical and DNA diagnostics for characterising multiple mechanisms of insecticide resistance in the peach-potato aphid, Myzus persicae (Sulzer).

The peach-potato aphid Myzus persicae (Sulzer) can resist a range of insecticides by over-producing detoxifying esterase and having mutant-insensitive forms of the target proteins, acetylcholinesterase (AChE), and the sodium channel. Using a combination of bioassays, biochemical and DNA diagnostics, it is now possible to diagnose all three mechanisms in individual aphids, and thereby establish their spatial distributions and temporal dynamics. A survey of 58 samples of wide geographic origin showed that all 46 resistant clones had amplified esterase genes (E4 or FE4) conferring broad-spectrum resistance to pyrethroids, organophosphates and carbamates. These occurred in combination with insensitive AChE (11 clones), conferring resistance to pirimicarb and triazamate, and/or mutant sodium channel genes (25 clones), conferring knockdown (kdr) resistance to pyrethroids and DDT. Amplified esterase genes were in linkage disequilibrium with both insensitive AChE and the kdr mutation, reflecting tight physical linkage, heavy selection favouring aphids with multiple mechanisms, and/or the prominence of parthenogenesis in many M. persicae populations. An ability to monitor individual mechanisms with contrasting cross-resistance profiles has important implications for the development of resistance management recommendations.