THE EFFECT OF INSECTICIDE TREATMENTS IN COTTON FIELDS ON THE LEVELS OF PARASITISM OF BEMISIA-TABACI (GENNADIUS) SL

Populations of whiteflies [Bemisia tabaci (Gennadius) sl.] and the rat es at which they were parasitized in cotton fields in Israel and Calif ornia were monitored over a number of years. Studies took place both i n fields that were treated with insecticides and in untreated fields a nd permitted us to assess the influence of insecticidal treatments upo n percentage parasitism. The results showed that, in many cases, insec ticide treatments had only a minor effect on levels of parasitism and that high levels of parasitism were sustained in insecticide-treated f ields. However, many repeated treatments, especially if monocrotophos was used, resulted in significant reductions in levels of parasitism i n Israel. Our findings suggest that the species of parasitoids we obse rved may be no more severely impacted by certain insecticides than nym phal whiteflies that serve as hosts. Nonetheless, reductions in parasi toid abundance may have important consequences for the biological cont rol of B. tabaci over time and over larger areas, and judicious use of insecticides in commercial cotton fields is warranted. (C) 1998 Acade mic Press.