CHANGES IN THE METHYLATION OF AMPLIFIED ESTERASE DNA DURING LOSS AND RESELECTION OF INSECTICIDE RESISTANCE IN PEACH-POTATO APHIDS, MYZUS-PERSICAE

Insecticide resistance in peach-potato aphids, Myzus persicae, results from the amplification of genes encoding an esterase that hydrolyses and sequesters insecticides, Resistance is normally stable, but highly resistant aphid clones sometimes lose resistance when insecticidal se lection pressure is removed, This loss of resistance, termed reversion , arises from a loss of elevated esterase enzyme through transcription al control, i.e. without loss of the amplified esterase DNA sequences, We have shown that loss of the elevated enzyme occurred simultaneousl y with loss of methylation at CCGG sites in the amplified DNA sequence s. During reselection of resistance in these revertant clones, enzyme levels increased, but there was no corresponding return of methylation to DNA sequences. Thus, although DNA methylation is closely correlate d with expression of the amplified esterase genes during reversion, it may not be a factor in the reverse process.