Testing for pesticide resistance in lettuce aphid

Lettuce aphid, Nasonovia ribisnigri Mosely (Hemiptera: Aphidoidae), was first detected in New Zealand on lettuce (Lactuca sativa) in Christchurch in March 2002. Lettuce growers immediately found the new pest difficult to control using insecticides. Failure of insecticides to provide adequate control could have been due to inadequate spray coverage because lettuce aphid prefers to feed in the interior of the lettuce or to insecticide resistance, which has been recorded in lettuce aphid in Europe. To determine the efficacy of topically applied insecticides on lettuce aphid in New Zealand, 12 pesticides were applied at recommended field rates with a Potter tower to apterous lettuce aphids on lettuce discs imbedded in agar. Only acephate (80.6%) and methomyl (90.7%) failed to give complete mortality after 48 hours at 18 degrees C. The concentration-mortality relationships for acephate, methomyl and pirimicarb were estimated and compared with data from Europe.