Current status of the greenhouse whitefly, Trialeurodes vaporariorum, susceptibility to neonicotinoid and conventional insecticides on strawberries in southern California.

Since 1998, the greenhouse whitefly, Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae), has emerged as a major insect pest of many horticultural crops in coastal California. Control of this pest has been heavily dependent upon chemical insecticides. Objectives of this study were to determine the status of the greenhouse whitefly susceptibility to neonicotinoid and conventional insecticides on strawberries in Oxnard/Ventura, a year-round intensive horticultural production area of southern California. For bioassay tests, adult whiteflies were collected from commercial strawberry crops, and immatures were directly developed from eggs laid by these adults. LD(50) values of soil-applied imidacloprid, thiamethoxam and dinotefuran were respectively 8.7, 3.2 and 4.9 times higher for the adults, 1.8, 1.2 and 1.5 times higher for the first-instar nymphs and 89.4, 390 and 10.4 times higher for the third-instar nymphs than their top label rates. LC(50) values of foliar-applied imidacloprid, thiamethoxam and acetamiprid were respectively 6.1, 6.0 and 1.7 times higher for the adults and 3.8, 8.7 and 4.4 times higher for the second-instar nymphs than their top label rates. For the adults, LC(90) values of endosulfan, malathion, methomyl, bifenthrin and fenpropathrin were 2.2, 1.2, 1.9, 2.3 and 4.9 times lower than their respective top label rates. Chlorpyrifos was not very effective against the adults, as indicated by its LC(90) being 120% higher than its top label rate. The present results strongly emphasize the need to develop resistance management strategies in the region.