Interactions among Helicoverpa armigera (Lepidoptera: Noctuidae), its larval endoparasitoid Microplitis croceipes (Hymenoptera: Braconidae), and Bacillus thuringiensis

Interactions among Helicoverpa armigera (Hubner), its larval endoparasitoid Microplitis croceipes (Cresson), and Bacillus thuringiensis Berliner were evaluated under laboratory conditions. Prefeeding H. armigera with lethal concentrations (0.08 and 0.16 mg/g) of Dipel (B. thuringiensis subsp, kurstaki strain HD-1) did not prevent M. croceipes from ovipositing in the infected host larvae. Development of parasitoid immatures in host larvae prefed for 24 or 48 h with the dietary B. thuringiensis was not adversely affected. However, feeding on the same diets for 72 h was detrimental to the parasitoid because of premature host mortality. Continuous exposure of H. armigera larvae to the diets at different time intervals after parasitization (0, 4, or 6 d), prevented successful development and pupation of M. croceipes, mainly caused by early mortality of the host. Feeding parasitoid adults with B. thuringiensis preparations of subsp. kurstaki strain HD-73 mixed in honey was not harmful to the wasps. Moreover, Dipel or purified B. thuringiensis spores of HD-73, but not purified crystals of this strain, increased longevity of the wasps compared with the control (honey alone). Microscopic observations and color indications showed that the adult parasitoid ingested the honey with the Dipel. The incompatibilities between application of B. thuringiensis to host larvae and parasitization with M. croceipes are discussed with regard to combining microbial and entomophagous control strategies against H. armigera.