Insecticide Resistance in Myzus Persicae (Sulzer) (Hemiptera: Aphididae) in Southeastern Australia

Strains of Myzus persicae, collected from the Goulburn Valley, Victoria, and the Bathurst‐Orange region, N.S.W., during 1988–89 and 89–90 were screened for resistance to demeton‐S‐methyl, pirimicarb, methamidophos and methomyl. Bioassay was used to determine levels of resistance to each chemical. Electrophoresis was used to determine the frequency of individual aphids with enhanced levels of the resistance conferring E4 carboxylesterase, which was assumed to be the resistance mechanism. Demeton‐S‐methyl resistance (RF range 14.8–40.0 x) and pirimicarb resistance (RF range 7.5–20.2 x) were detected in all strains tested by bioassay. Low level methamidophos resistance was detected (RF range 2.9–4.2 x) in three of the seven strains tested. However, methomyl resistance was not detected in any strain. Electrophoretic examination of the resistant strains showed only one strain contained susceptible individuals. Most strains consisted predominantly of the highly resistant variant (R2) and some strains may contain the extremely resistant variant (R3).