Effects of malathion bait spray on Aleyrodes spiraeoides (Homoptera: Aleyrodidae) and its parasitoids in northern California

During an infestation of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), in northern California, malathion-Staley's bait was sprayed as an eradicant. As a part of a study on the effect of this spray on nontarget organisms, Aleyrodes spiraeoides Quaintance and two of its chalcidoid parasitoids, Euderomphale flavimedia (Howard) and Encarsia peltata (Cockerell), were chosen as index species. Simulated aerial bait sprays were used to test effects of the spray, on foliage on the longevity, production of progeny, and presence on foliage of test insects. The sedentary feeding behavior and preference for the undersides of leaves protected the whitefly from severe intoxication. The more active parasitoids were highly susceptible. Despite similar adult susceptibility, Encarsia was significantly more successful than Euderomphale in parasitizing whiteflies. Bait-sprayed foliage was relatively free of adult parasitoids; test results suggested some degree of active avoidance or enhanced dispersal by the wasps in addition to mortality because of bait. No significant increase or decrease in numbers of Aleyrodes was observed over the short term despite significant reductions in activities of its parasitoids.