CONTROL STRATEGY FOR THE SWEET-POTATO WHITEFLY, BEMISIA-TABACI, LATE IN THE COTTON-GROWING SEASON

Populations of the sweetpotato whitefly, Bemisia tabaci (Gennadius), were sampled late in the cotton-growing seasons of 1990, 1991 and 1992, in commercial 'Acala' cotton fields in southwestern Israel. In mid summer, when populations of B. tabaci started to build up, cotton fields were commercially treated with a single application of an IGR (insect growth regulator). The experimental plots were then treated in September with conventional adulticides or with the novel insecticides buprofezin and pyriproxyfen (IGR), and diafenthiuron (a thiourea derivative). The effects of the insecticides on B. tabaci larval and adult populations, and the amount of damage to the cotton lint, were recorded. Untreated populations of larvae and pupae of B. tabaci in the three end-of-season studies, had the tendency to build up toward the defoliation treatment. However, the level of the B. tabaci populations observed in the experimental fields and the short period of exposure of the open cotton bells to the whiteflies, did not result in lint damage, probably because the whitefly numbers had been reduced considerably after the defoliation treatment. At the end of the 1991 and 1992 cotton seasons, a high level of parasitism, ranging between 50% and 80%, was recorded. The shift in chemical applications toward the novel IGRs during the season, along with the reduction in insecticide use in general, probably contributed to the propagation of parasitoids, thereby improving whitefly control.