Resistance of Bemisia tabaci (Homoptera : Aleyrodidae) to insecticides in southern Spain with special reference to neonicotinoids

The tobacco whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) whi ch occurs in various parts of the world, has developed a high degree of res istance against several chemical classes of insecticide, including organoph osphates, carbamates, pyrethroids, insect growth regulators and chlorinated hydrocarbons. The present studies were done in order to monitor tho suscep tibility of whitefly populations in southern Spain to insecticides commonly used there. Systemic bioassays using Spanish field populations of B tabaci collected in 1994, 1996 and 1998 indicated an increase, albeit a slow one, in resistance to imidacloprid over this period. Comparative studies of oth er neonicotinoids using the same bioassay revealed a high degree of cross-r esistance to acetamiprid and thiamethoxam, Leaf-dip bioassays with adult fe males from these populations revealed a high level of resistance to cyfluth rin, endosulfan, monocrotophos, methamidophos, and pymetrozine, each at 200 mg litre (1). Buprofezin and pyriproxyfen were tested against second-insta r nymphs and eggs, respectively, Buprofezin also showed a lower efficacy ag ainst ESP-98, a strain of B tabaci received from Almeria in 1998, but pyrip roxyfen resistance was not obvious when tested against eggs of strain ESP-9 8, Field trials in 1998 revealed good efficacy of imidacloprid in one farm In the Almeria region and two greenhouses in Murcia and Sevilla, but a loss of activity by imidacloprid In another farm in the Almeria region. Cross-r esistance between imidacloprid and thiamethoxam was also confirmed under he ld conditions. (C) 2000 Society of Chemical Industry.