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 rates at which they were parasitized in cotton fields in Israel and California were monitored over a number of years. Studies took place both in fields that were treated with insecticides and in untreated fields and permitted us to assess the influence of insecticidal treatments upon percentage parasitism. The results showed that, in many cases, insecticide treatments had only a minor effect on levels of parasitism and that high levels of parasitism were sustained in insecticide-treated fields. However, many repeated treatments, especially if monocrotophos was used, resulted in significant reductions in levels of parasitism in Israel. Our findings suggest that the species of parasitoids we observed may be no more severely impacted by certain insecticides than nymphal whiteflies that serve as hosts. Nonetheless, reductions in parasitoid abundance may have important consequences for the biological control of B. tabaci over time and over larger areas, and judicious use of insecticides in commercial cotton fields is warranted. (C) 1998 Academic Press.