MANAGING RESISTANCE IN BEMISIA-TABACI IN ISRAEL WITH EMPHASIS ON COTTON

At the beginning of the 1990s, insecticides with novel modes of action, such as buprofezin, pyriproxyfen and diafenthiuron, were introduced for controlling the whitefly Bemisia tabaci (Gennadius) in cotton and other crops. In order to delay the onset of resistance to these novel insecticides, as well as to the efficient conventional ones, an insecticide resistance management (IRM) strategy was implemented in 1987 in cotton fields in Israel. The main purposes have been to combat resistance to available, efficient insecticides and to prolong the life-span of new insecticides by optimizing their use and preserving natural enemies during the peak of their activity. A rotation programme was applied, using insecticides of different modes of action, rotated according to the generation duration of the relevant pests. The strategy included explanatory and educational campaigns, and was accompanied by an extensive resistance monitoring programme conducted throughout the year in greenhouses and during the summer in cotton fields. Bioassays of whiteflies collected from cotton fields indicated that one treatment with pyriproxyfen in cotton fields during a one-month period, followed by an additional treatment with buprofezin (if required), did not markedly alter the susceptibility of B. tabaci to either compound. In addition, no appreciable increase of resistance to the available conventional insecticides was observed, although some changes in susceptibility were noticed during the cotton season. In some greenhouses without an IRM programme, a c. tenfold increase in resistance to buprofezin was found after two or three applications of this compound in each season. A c. 500-fold increase of resistance to pyriproxyfen was recorded after three successive applications of this compound in a greenhouse. These findings demonstrate the necessity for an IRM strategy to be implemented in both open fields and greenhouses.