Structuration of multilocus genotypes associated with insecticide resistance of the peach potato aphid, Myzus persicae (Sulzer), in potato fields in southern Belgium.

Background: The peach potato aphid, Myzus persicae, has developed resistance to many insecticides. In Belgium, M. persicae is one of the most common aphids in potato fields and one of the most effective virus vectors. We monitored resistance mutations to pyrethroids, carbamates and neonicotinoids and related these results to microsatellite genotyping to provide information to support the choice of management tactics.

Results: Most of the 254 aphids tested (97.6%) displayed at least one mutation conferring resistance to pyrethroids (L1014F, M918L and M918T) and 36.2% additionally carried the modified acetylcholinesterase (MACE) carbamates resistance making them resistant to two insecticide action modes. Ten mutation combinations were detected, two of which were frequent and a strong linkage was found between MACE and M918L mutations. The R81T mutation conferring resistance to neonicotinoids was not detected. Microsatellites highlighted a moderate genetic diversity [69 multilocus genotypes (MLG) detected], severe deviations from Hardy-Weinberg expectations, a highly significant excess of heterozygotes and linkage disequilibrium between all pairs of loci. A structuration of MLGs in association with the mutation combinations was observed. Genetic differentiation was mainly not significant between sampling locations and most MLGs were geographically widespread. These results suggest the likely coexistence of parthenogenesis (obligatory or facultative) and sexual reproduction, and the existence of 'old' parthenogenetic overwintering asexual lineages.

Conclusion: The results of this monitoring at a regional scale provide useful information on insecticide resistance, genetic diversity and reproductive modes, and highlight the need to reduce the insecticide selection pressure and to implement mitigating techniques.