The longevity of 2 primary parasitoids of aphids, Aphidius liriodendrii and Trioxys curvicaudus, was severely reduced when they were exposed in the laboratory to a malathion bait spray used to eradicate Ceratitis capitata. The longevity of several hyperparasitoids of A. liriodendrii and T. curvicaudus was also reduced. Oviposition of A. liriodendrii was severely reduced on plants that received field applications of malathion bait spray. The parasitoids appeared neither attracted to nor repelled by the malathion bait. Pesticide contact occurred during apparently random searching by the parasitoids. As T. curvicaudus is reportedly responsible for the biological control of its aphid host Eucallipterus tiliae, malathion bait sprays used for C. capitata control may cause an increase in aphid populations by reducing the effectiveness of primary parasitoids.