Peach potato aphid, Myzus persicae (Sulzer) is an important agricultural pest throughout the world. Due to extensive and repeated application of insecticides, this aphid has developed different resistance mechanisms. Resistance mechanisms to pirimicarb and oxy-demeton methyl were surveyed. Insecticide bioassay was carried out on seven populations, collected from north provinces, as well as Karaj, using topical application method. The results of bioassay indicated that Talesh, Tirtash, Plangar and Karaj populations are susceptible to pirimicarb and oxy-demeton methyl. The results of inhibition assay showed that I50 of pirimicarb for Karaj, Rasht and Resistant populations are 1.365×10-8M, 1.366×10-8M and 1.89×10-5 M, respectively. Also I50 of oxy-demeton methyl for Karaj, Rasht and Resistant populations are 7.566× 10-7M, 8.236 ×10-7M and 2.11×10-6M, respectively. The insensitivity ratios of acetylcholinesterase from resistant population to pirimicarb and oxy-demeton methyl were 1384.6 and 2.7 respectively. The results suggested that acetycholinesterase of resistant population is insensitive to pirimicarb and oxy- demeton methyl.
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