The Ser431Phe substitution in acetylcholinesterase associated with pirimicarb and organophosphorous insecticide resistance in the peach-potato aphid, Myzus persicae (Hem.: Aphididae)

The peach-potato aphid, Myzus pesicae Sulzer, is a globally distributed, economically important pest of a wide range of field crops and ornamentals. Due to extensive and repeated use of insecticide, this species has developed many different resistance mechanisms to insecticides. The enzyme acetylcholinesterase (EC 3.1.1.7) (AChE) occurs widely in both vertebrate and invertebrate nervous systems and is the target of organophosphate (OP) and carbamate insecticides. One of resistance mechanisms to OP and carbamate insecticides is the insensitivity of AChE to these insecticides. In this study the possibility of mutation in insensitive AChE was surveyed. The complete coding sequences of acetylcholinesterases (MpAChE2) from susceptible and resistant populations were identified and sequences from resistant and two susceptible populations were compared. Consequently, one amino acid substitution (Ser431Phe) was detected within the resistant population at MpAChE2 gene. The Ser431Phe substitution is located in acyl pocket of acetylcholinesterase. Therefore, it seems that MpAChE2 is important as a target of pirimicarb. This substitution makes the acyl pocket narrower and pirimicarb can not have any access to this site. cDNA was obtained from individual aphids randomly and sequence of MpAChE2 indicated that MpAChE2 of the resistant population was heterozygous.