MANAGING RESISTANCE IN INSECT GROWTH-REGULATORS IN THE SWEET-POTATO WHITEFLY (HOMOPTERA, ALEYRODIDAE)

Insecticide resistance in the sweetpotato whitefly, Bemisia tabaci (Gennadius), was monitored during 1991 and 1992 in a rose greenhouse and in adjacent cotton fields located in the western Negev of Israel. The whiteflies were collected and exposed to a series of concentrations of the insect growth regulators (IGRs) buprofezin and pyriproxyfen. Assays done on whiteflies obtained from the greenhouse indicated an almost-equal-to 4-fold increase in tolerance to buprofezin after two successive applications of this compound. A relatively high level of resistance to pyriproxyfen was recorded after three successive applications of this compound. At LC50, the resistance ratio value for suppression of egg-hatch was 554-fold; for adult emergence failure, the resistance ratio was 10-fold. In contrast, one treatment of pyriproxyfen in cotton fields during the summer seasons (in accordance with the cotton insecticide resistance management [IRM] strategy) did not alter the susceptibility of B. tabaci appreciably to this compound. The rapid development of resistance to the novel IGRs demonstrates the need for IRM strategy, in both field and greenhouse crops. To prevent development of resistance to these compounds, use of both pyriproxyfen and buprofezin should be restricted to one treatment per crop season during the period of peak activity of the pest.