Inheritance of the amplified esterase genes responsible for insecticide resistance in Myzus persicae (Homoptera: Aphididae)

Insecticide-resistant and susceptible clones of Myzus persicae were induced to produce sexual morphs and crossed in the laboratory. Progeny clones were analysed for karyotype, esterase (E4, FE4 or S) gene type and activity, and amplified E4 and FE4 genes were located on their chromosomes by fluorescence in situ hybridization (FISH). Amplified FE4 genes of resistant parent clones (800F and French R) were inherited according to expectations. Chromosomal locations of these genes (on autosomes 1 and 3 in 800F, and on 1 and 2 in French R) were confirmed by FISH analysis of progeny that had inherited an autosome 2 marker (a dissociation) from the susceptible parent (DS). Inheritance of amplified E4 genes could not be studied directly as none of the available clones was able to produce mating females. Males from two clones with amplified E4 genes (and with the A1,3 translocation that is common to all E4-producing genotypes) were therefore mated with females from clones with amplified FE4 genes at known chromosomal locations. Progeny were obtained with both E4 and FE4 genes, a combination not yet found in nature. Analysis of F-1 and subsequent generations confirmed that the amplified E4 site on autosome 3(T) is close to the translocation breakpoint, and apparently coallelic with the amplified FE4 site on the normal autosome 3 inherited from 800F. One of the translocated parent clones (4156) had two additional E4 sites, unlinked to the translocation, which were inherited according to expectation. Esterase activities of progeny clones, measured by immunoassay, mostly corresponded to the number of amplified sites inherited, with some discrepancies which could be attributed to copy number differences between sites, inheritance of partially methylated genes from French R, or position effect variegation at the site on 3(T). Inheritance of the A1,3 translocation in two crosses differed markedly from expectation.