The longevity of two primary aphid parasitoids,Aphidius liriodendriiLiu andTrioxys curvicaudus(MacKauer), was severely reduced when they were exposed in the laboratory to a malathion bait spray used to eradicate the Mediterranean fruit fly,Ceratitis capitata(Wiedemann). The longevity of several hyperparasites ofA. liriodendriiandT. curvicaudusalso was reduced. Oviposition ofA. liriodendriiwas 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. AsT. curvicaudusis reportedly responsible for the biological control of its aphid host,Eucallipterus tiliae(L.), malathion bait sprays used for Mediterranean fruit fly control may cause an increase in aphid populations by reducing the effectiveness of primary parasitoids.