USE OF BIOCHEMICAL AND DNA DIAGNOSTICS FOR CHARACTERIZING 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 i nsecticides by over-producing detoxifying esterase and having mutant-i nsensitive 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 mechanis ms in individual aphids, and thereby establish their spatial distribut ions and temporal dynamics. A survey of 58 samples of wide geographic origin showed that all 46 resistant clones had amplified esterase gene s (E4 or FE4) conferring broad-spectrum resistance to pyrethroids, org anophosphates and carbamates. These occurred in combination with insen sitive AChE (11 clones), conferring resistance to pirimicarb and triaz amate, and/or mutant sodium channel genes (25 clones), conferring knoc kdown (kdr) resistance to pyrethroids and DDT. Amplified esterase gene s were in linkage disequilibrium with both insensitive AChE and the kd r mutation, reflecting tight physical linkage, heavy selection favouri ng aphids with multiple mechanisms, and/or the prominence of parthenog enesis in many M. persicae populations. An ability to monitor individu al mechanisms with contrasting cross-resistance profiles has important implications for the development of resistance management recommendat ions.