Survey of enzyme variation in british populations of Myzus persicae (Sulzer) (Hemiptera: Aphididae) on crops and weed hosts

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Abstract
Electrophoretic variation of eight enzymes (thirteen loci) including esterase-4 (EST-4, the enzyme conferring insecticide resistance) was studied in clones of Myzus persicae (Sulzer) from several localities in south-eastern England (major beet and rape growing areas) and from a site in mid-Scotland (a seed potato growing region). All loci except esterase-1/-2, which showed putative allelic variation with slow (EST-1) and fast (EST-2) bands, and EST-4, which occurred as three principal quantitative variants (susceptible (S), resistant (R1) and highly resistant (R2)), were found to be monomorphic. The occurrence of the insecticide-resistant variants is reported and shown to differ little from previous surveys, with frequencies of R1 aphids on rape in south-eastern England appearing close to fixation (>0·9), probably due to continued insecticide selective pressure. The general lack of qualitative (i.e. mobility) variation at the loci examined is thought to be due to the species having gone through tight population bottlenecks in the past, which have systematically eliminated the rarer alleles, driving the most common to fixation. Consequently, as the data suggest, only a small number of M. persicae genotypes may exist in Britain.
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