Choosing the right plant: how aphids react to the anti-feeding effect of imidacloprid in tobacco

Neonicotinoid pesticides are widely used for pest control in cultivated tobacco (Nicotiana tabacum) in North Carolina, with imidacloprid being the most dominant active ingredient used by our growers. Imidacloprid is regularly applied before transplant; it gets absorbed through the roots and moves through the xylem of the plant, offering systemic protection against piercing-sucking pests. Besides its toxicity, imidacloprid also has an anti-feeding effect that, in theory, improves its effectiveness as a pesticide. We investigated if apterous female aphids could detect the pesticide before feeding. We put 20 adult aphids in arenas with four leaf discs. In choice experiments each disc belonged to one pesticide treatment (untreated control, 0.005X, 0.01X and 0.02X) and in no-choice experiments all four discs had the same treatment. Each arena was replicated four times and we ran the experiments two independent times. We analyzed adult mortality and total nymph production after 72 hours of exposure. The no choice experiment showed that all three pesticide concentrations significantly reduced reproduction, but reproduction was never zero, suggesting that aphids start feeding and reproducing in treated plants before detecting the presence of the pesticide. There were no significant differences in adult mortality between the different no-choice treatments. Choice experiments showed similar results. These experiments demonstrate that the anti-feeding effect is elicited after the aphid has pierced the leaf and that adults might survive for a few days after exposure. These results could have implications in virus dispersal by aphids.