Aspects of insecticide resistance and reproductive biology ofAphis gossypii glover on seed potatoes

For several years the aphid population patterns and the incidence of the main potato virus diseases have been monitored in Italian potato-growing areas. Starting from 1992, an increase in Aphis gossypii? as compared to Myzus persicae, Macrosiphum euphorbiae and Aphis fabae, was observed on seed potato fields in the north of Italy.Laboratory tests revealed that A. gossypii was insensitive to the pesticide pirimicarb, even at the maximum dose tested (2400 mu g/ml). Moreover, in the presence of pirimicarb the reproductive capacity increased up to 30% as compared with the control, and the new-born aphids began to appear 2 days earlier in the treated group. By contrast, M. persicae was controlled at a lower dose (300 mu g/ml). Lambda-cyhalothrin and imidacloprid were very effective against both aphids.