The cotton whitefly, Bemisia tabaci (Genn.), is parasitized by four Aphelinid species: Eretmocerus diversiciliatus Silv., E. mundus Merc., Encarsia lutea Masi. and an unidentified Encarsia sp Whitefly adults move from field weeds onto cotton during the period September–November. The application of broad-spectrum insecticides to control other cotton pests early in the season prevents the establishment of the host-stage of B. tabaci needed by the parasitoids within cotton fields during September and October. The rate of parasitism is consequently decelerated to peak in January towards the end of the season. Peak per cent parasitism for treated cotton fields was 36.7 as compared to 76.8 in untreated fields. This has promoted B. tabaci to an all season pest instead of an early and mid-season occasional pest. Alternative control strategies for early season pests are discussed.
