THIRD TROPHIC LEVEL EFFECTS OF AZADIRACHTIN

Azadirachtin (AZA) is the principal insecticidal compound occurring in the oil of neem [Azadirachta indica (Juss.)] seed. Although many studies have been published (Schmutterer 1990) regarding the effects of AZA on herbivorous insects, little is known of the impact of this compound on the natural enemies of herbivores. Beckage et al. (1988) investigated the effects of injected AZA on Cotesia congregata (FAY) (Braconidae), a parasitoid of Manduca sexta (L.). Parasitoid development was retarded when injections of 2.5–10 μg AZA were administered to the host larva prior to the wasp's first larval ecdysis. The development of new neem-based insecticides in North America (Isman et al. 1991) has prompted the investigation of the effects of AZA on the natural enemies of pest insects that have ingested sublethal doses of the active compound. Our laboratory study was carried out with the ichneumonid parasitoid, Diadegma terebrans (Gravenhorst), and its host, the European corn borer, Ostrinia nubilalis (Hubner). AZA (>95% purity) for this study was extracted as described previously (Xie et al. 1991) from seeds collected in India.