Idiosyncratic life-histories of organisms can impose interesting constraints on the dynamics of resistance genes and the likely success of resistance management tactics. This is exemplified well by aphids, whose life-cycles can range from obligate holocycly to obligate anholocycly, with some species exhibiting both strategies in different geographical regions. In the UK and elsewhere in northern Europe, the peach-potato or green peach aphid (Myzus persicae) is largely anholocyclic, consisting of relatively few clonal lineages, each with a characteristic and constant suite of resistance genotypes. As a result, genotypic combinations that ought to exist, don't exist, or are massively under-represented. Instead, the dynamics of resistance reflects the outcome of inter-clonal selection across the genome as a whole rather than selection of allelic variants at individual loci. This 'congealing' and persistence of multi-locus and co-adapted genotypes within clones has interesting and important implications for tactics aimed at combating established and new resistance mechanisms. It can both buffer existing resistance genes from the interplay of fitness costs and insecticide use that occurs in sexually-outcrossing organisms, and can also (more speculatively) buffer against the rapid invasion of novel resistance genes, whose establishment may depend on their incorporation, through recombination, into locally-adapted gene pools. Another example concerns the grain aphid (Sitobion avenae), in which a mutation conferring pyrethroid resistance seems locked into a life of permanent heterozygosity unless some very rare events intervene.

No sex please, we're British: Resistance behaving badly

248th National Meeting (2014)

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