Influence of pesticide treatments on the dynamics of whiteflies and associated parasitoids in snap bean fields

To determine the influence of pesticide treatments on the population dynamics of the whiteflies Trialeurodes vaporariorum (Westwood) and Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) and their naturally occurring parasitoids, we performed field experiments on insecticide sprayed and unsprayed fields during a cropping season of snap bean in Pradera, Valle del Cauca, Colombia. Substantially larger populations of whitefly nymphs occurred in the unsprayed field than in the sprayed field. Parasitoids were more frequent in unsprayed than in sprayed fields with Encarsia nigricephala Dozier being more prevalent than Amitus fuscipennis MacGown & Nebeker. In sprayed fields the nymphs parasitized by E. nigricephala exceeded the unparasitized whitefly nymphs at the end of the cropping season. Our results suggest that while under current agricultural practices whiteflies on snap beans cannot be exclusively controlled by naturally occurring parasitoids, parasitoids may be integrated with chemical control in order to reduce crop damage