ABSTRACT
BACKGROUND: The accuracy of predicting the survival of insecticide-resistant aphids following the application of commonly used insecticides from the carbamate, the pyrethroid, a mix of the two or the neonicotinoid chemical classes was evaluated in a potato field in Scotland. Equal proportions of five genotypes of the peach-potato aphid, Myzus persicae (Sulzer), with none, resistance to dimethyl-carbamates, resistance to pyrethroids or combinations conferring resistance to both chemical classes were released into potato field plots. The insecticides were sprayed separately onto these plots, the aphid populations were analysed after 6-8 days and the process repeated. RESULTS: For each assessment after the three separate spray events, plots treated with the carbamate had 48, 147 and 28%, those treated with pyrethroid 53, 210 and 89%, those treated with carbamate/pyrethroid 28, 108 and 64% and those treated with neonicotinoid 43, 55 and 11% of the numbers of M. persicae by comparison with untreated controls. Only the proportions of surviving aphids from the genotype containing no insecticide resistance traits and the genotype containing elevated carboxylesterases matched ratios predicted from the selective advantage afforded by the resistance traits alone. Survival of aphids from the other three genotypes that carried 1-3 of the insecticide resistance traits differed from expectations in all cases, possibly owing to physiological differences, including their vulnerability to predators and hymenopterous parasitoids present at the site and/or their carrying unknown insecticide resistance mechanisms. CONCLUSION: Control strategies based on knowledge of the genetically determined insecticide resistance profile of an M. persicae population alone are insufficient. Hence, other important factors contributing to aphid survival under insecticide pressure need to be considered.
