Effects of cowpea intersowing and insecticide application on Helicoverpa armigera Hubner (Lepidoptera : Noctuidae) and its natural enemies in pigeonpea intercropped with sorghum

In a split-plot experiment, Helicoverpa armigera eggs, larvae, and H, armig era egg predators were sampled weekly or biweekly to test whether intersowi ng of cowpea could increase the natural control of Helicoverpa armigera in pigeonpea that had been relay intercropped with sorghum, and to test the ef fect of an insecticide treatment on the H. armigera population and on its n atural enemies. Cowpea intersowing resulted in higher numbers of H. armiger a eggs and larvae per pigeonpea plant in the first 3 weeks of sampling, whe reas the predator species studied were not significantly affected, possibly due to the small overlap between the composition of natural enemies in sor ghum and pigeonpea: the two beneficial species Orius tantillus (Motschulsky ) (Heteroptera: Anthochoridae) and Menochilus sexmaculatus F. (Coleoptera: Coccinellidae), very common predators in sorghum, occurred in low numbers i n pigeonpea, where the most common predators were Cheiracanthium inornatum O.P.-Cambridge (Aranea: Clubionidae) and anthicids (Anthicus sp., Formicomu s sp.) (Coleoptera: Anthicidae). Insecticide treatment resulted in signific antly higher number of H, armigera eggs per plant compared with no insectic ide treatment, the effect being most pronounced immediately after the treat ment. Insecticide had no significant effect on the number of H. armigera la rvae per plant, but it had a strong adverse effect on C. inornatum and anth icids.