none Heliothis virescens; HYMENOPTERAN-PARASITES; Microplitis croceipes; Parasite development, effect of bacterial contamination Microplitis croceipes; LARVAL-DEVELOPMENT; Lepidopteran host, effect of bacterial contamination; BACTERIAL-DISEASES; Bacillus, Escherichia, Leuconostoc & Pseudomonas; Larval mortality, relative susceptibility in lepidopteran host; MORTALITY-; Larvae, bacterial contaminated lepidopteran host. Bacterial contaminants of Heliothis virescens (F.) influenced the development of Microplitis croceipes (Cresson). Among the four bacterial species studied, the most virulent was Pseudomonas maltophilia Hugh and Ryschenkow followed by Bacillus subtilis (Ehrenberg) Cohn. Both bacteria caused severe mortality in all stages of Microplitis tested. Microplitis larvae were less suceptible to Escherichia coli (Migula) Castellani and Chalmers and Leuconostoc mesenteroides (Tsenkovskii) van Thieghem than to B. subtilis and P. maltophilia. Although E. coli did not affect the number of cocoons produced, adult emergence was lower than in controls. Longevity of adult Microplitis exposed to bacterially contaminated honey-water was greatly reduced in all bacterial treatments.