Why are there so few resistance–associated mutations in insecticide target genes?

Abstract

The genes encoding the three major targets of conventional insecticides are: Rdl , which encodes a γ–aminobutyric acid receptor subunit (RDL); para , which encodes a voltage–gated sodium channel (PARA) and Ace , which encodes insect acetylcholinesterase (AChE). Interestingly, despite the complexity of the encoded receptors or enzymes, very few amino acid residues are replaced in different resistant insects: one within RDL, two within PARA and three or more within AChE. Here we examine the possible reasons underlying this extreme conservation by looking at the aspects of receptor and/or enzyme function that may constrain replacements to such a limited number of residues.