PYRIPROXYFEN, A NOVEL INSECT GROWTH-REGULATOR FOR CONTROLLING WHITEFLIES - MECHANISMS AND RESISTANCE MANAGEMENT

Pyriproxyfen, a novel juvenile hormone mimic, is a potent suppressor of embryogenesis and adult formation of the sweetpotato whitefly, Bemisia tabaci (Gennadius), and the greenhouse whitefly, Trialeurodes vaporariorum (Westwood). Dipping of cotton or tomato seedlings infested with 0 to 1-day-old eggs in 0.1 mg litre(-1) resulted in over 90% suppression of egg hatch of both B. tabaci and T. vaporariorum. Older eggs were affected to a lesser extent. Exposure of whitefly females to cotton or tomato seedlings treated with pyriproxyfen resulted in oviposition of non-viable eggs. The LC(90) values for egg viability of B. tabaci and T.uaporariorum exposed to treated plants were 0.05 and 0.2 mg litre(-1), respectively. Treatment of whitefly larvae with 0.04-5 mg litre(-1) resulted in normal development until the pupal stage; however, adult emergence was totally suppressed. Second instars of B. tabaci exposed to 5 mg litre(-1) pyriproxyfen, excreted honeydew at a level similar to the control level until the fourth instar (pupation), after which a strong reduction was observed. Inhibition of egg-hatch on the lower surface of cotton leaves was observed when their upper surface was treated with 1-25 mg litre(-1), indicating a pronounced translaminar effect. These findings indicate that pyriproxyfen is an efficient control agent of both B. tabaci and T. vaporariorum. The compound has been used successfully for controlling whiteflies in Israeli cotton fields since 1991. Adults of B. tabaci collected from a rose greenhouse and from adjacent cotton fields were monitored during 1991-1993 for their susceptibility to pyriproxyfen. A high level of resistance was recorded in whiteflies collected from a greenhouse after three successive applications of pyriproxyfen. Based on LC(50) values, the resistance ratio for egg-hatch suppression was 554-fold and, for adult emergence failure, 10-fold. However, a single treatment of pyriproxyfen in cotton fields during the summer season (according to an insecticide resistance management (IRM) strategy) did not alter appreciably the susceptibility of B. tabaci to this compound. In order to prevent development of resistance, an attempt should be made to restrict its use to one treatment per crop season applied during the peak activity of the pest. Pyriproxyfen can be alternated with other novel compounds such as buprofezin and diafenthiuron for controlling whiteflies in cotton, vegetables and ornamentals as part of integrated pest management (IPM) and IRM strategies. In pyriproxyfen- or buprofezin-resistant strains of B. tabaci or T. vaporariorum, no appreciable cross-resistance was observed among pyriproxyfen, buprofezin and diafenthiuron.