Heliothis virescens; Pseudoplusia includens; DEVELOPMENT-; Hymenopteran parasite calyx fluid & venom influences; HYMENOPTERAN-PARASITES; Microplitis demolitor; Parasite calyx fluid & venom effects on host development Microplitis demolitor; TOXINS-AND-VENOMS; Venom effects on lepidopteran hosts development; DUCTS-OF-FEMALE; Calyx fluid effects on lepidopteran host development; LEPIDOPTERAN-HOSTS; Heliothis virescens & Pseudoplusia includens; Parasite calyx fluid & venom effects on host development; VIRAL-DISEASES; Polydnavirus; Parasite calyx fluid effects on lepidopteran hosts development Calyx fluid and venom from the braconid parasitoid Microplitis demolitor differentially affected the development of Pseudoplusia includens and Heliothis virescens. P. includens exhibited delays in larval development, supernumerary instars, and formed larval-pupal intermediates when injected with 0.01-0.10 wasp equivalents of calyx fluid. In contrast, H. virescens was relatively unaffected by calyx fluid regardless of dose. Venom did not affect the development of either host species, but appeared to synergize the activity of calyx fluid. This was particularly evident in H. virescens, where injection of 0.10-0.20 wasp equivalents of calyx fluid and venom induced the formation of a large number of intermediates while the same amount of calyx fluid did not. The particulate portion of M. demolitor calyx fluid was the only component that caused developmental delays and the formation of intermediates in both host species. Purified virus caused developmental alterations in P. includens, while trioxsalen treated calyx fluid did not affect development of P. includens or H. virescens. These data suggest the requirement for venom in parasitism may differ between host species, and that dosage plays an important role in interpreting the interaction between calyx and venom components. none