Behavioural effects of imidacloprid, a new nicotinyl insecticide, on the potato aphid, Macrosiphum euphorbiae (Thomas) (Homoptera, Aphididae)

Adult potato aphids, Macrosiphum euphorbiae (Thomas), caged on potato terminal leaflets treated systemically with imidacloprid solutions ranging between 5.4 x 10(-4) and 5.4 x 10(-8) mt per mt water showed a significant reduction in the distance they travelled, time taken to travel a given distance, and flight propensity but no significant differences in the frequency or duration of short probing behaviour. The frequency of adult apterous potato aphids colonizing untreated potato leaflets or leaflets treated with an imidacloprid solution (5.4 x 10(-4) mt per mt water) was not significantly different, indicating no repellency. Potato aphids moving from systemically treated to untreated leaflets did not recover much and their reduced walking ability was maintained for days. A 3-day exposure to vapour from an imidacloprid solution (5.4 x 10(-4) mt per mt water) did not produce significant mortality or changes in nymphal production. The daily cumulative mortality obtained by caging potato aphids on potato leaflets placed in an imidacloprid solution (5.4 x 10(-7) mL per mL water) was similar to that obtained in the field, on 20-day-old plants treated at planting with imidacloprid applied at 0.02 g AI/m. None of the rates of imidacloprid tested stimulated the dispersal of apterous or alate potato aphids.