Variation in the chromosomal distribution of amplified esterase (FE4) genes in Greek field populations of Myzus persicae (Sulzer)

In northern Greece, insecticides have been used intensively against aphid populations of the Myzus persicae group, both on its primary host peach, on which annual sexual reproduction occurs, and on secondary host held crops such as tobacco, on which reproduction is entirely parthenogenetic. This has resulted in the selection of high levels of resistance based on the amplification of two genes encoding insecticide-degrading esterases, E4 and FE4. We have used fluorescence in situ hybridization (FISH) to study variation in the number and distribution of loci with amplified esterase genes in clones established from field populations of M. persicae-group aphids sampled on various crops in northern Greece. All clones collected from peach, as well as most of the clones (74%) from tobacco and other secondary host plants, had amplified FE4 genes and were of normal karyotype. Amplicon clusters containing FE4 occurred at multiple sites which varied in number, zygosity and distribution between clones. Most loci were on autosome 1, which also had the only site that was consistently occupied by amplified FE4, situated near subtelomeric repetitive DNA. Possibly this was the original site of FE4 gene amplification, and the location of the single-copy 'wild type' esterase genes. The rest of the clones from tobacco and other secondary hosts (26%) had amplified E4 genes, and all those analysed by FISH had an amplicon cluster on autosome 3(T) at a site close to the breakpoint of an A1,3 translocation, confirming the close linkage of this translocation with, and its probable involvement in, E4-based resistance. Three translocated clones collected on capsicum at one site had both E4 and FE4 amplified, the first time that both esterase gene types have been found together in individual aphids from field populations.