Susceptibility of Arizona Whiteflies to Neonicotinoid Insecticides and IGRs: New Developments in the 1999 Season

Whiteflies are serious pests of cotton, melons, and winter vegetables in Arizona’s low deserts. Successful management of whiteflies requires an integrated approach, a critical element of which is routine pest monitoring. In this paper we report findings of our 1999 investigations of resistance of Arizona whiteflies to insect growth regulators (IGRs) and neonicotinoid insecticides. Whiteflies collected from cotton fields, melon fields and greenhouses were tested for susceptibility to imidacloprid (Admire /Provado), and two other neonicotinoid insecticides, acetamiprid and thiamethoxam, and to two insect growth regulators (IGRs), buprofezin (Applaud ) and pyriproxyfen (Knack ). Contrasts of 1999 and 1998 results indicated increased susceptibilities, on average, to both imidacloprid and buprofezin of whiteflies collected from cotton. A cropping system study showed that whiteflies collected from spring melons had significantly lower susceptibility to imidacloprid than those collected from cotton or fall melons. The opposite was found for pyriproxyfen, to which whiteflies from cotton and fall melons had lower susceptibility than those from spring melons. As in 1998, whiteflies with reduced susceptibility to imidacloprid continue to be found in certain locations, particularly in spring melon fields and greenhouses. Results of our laboratory bioassays on susceptibility of Arizona whiteflies to neonicotinoid insecticides provided evidence of a low order cross-resistance between imidacloprid, acetamiprid and thiamethoxam. Monitoring in 1999 provided the first evidence of reduced susceptibility of Arizona whiteflies to pyriproxyfen.