none Heliothis virescens; PROTEINS-; Haemolymph levels; HAEMOLYMPH-; Protein & ecdysteroid levels; HORMONES-; Ecdysteroid levels; LARVAL-DEVELOPMENT; METAMORPHOSIS-; Pupation, hymenopteran parasite teratocytes effects; HYMENOPTERAN-PARASITES; Cardiochiles nigriceps; Parasite teratocytes effects on host development & ecdysteroid production Cardiochiles nigriceps; EGG-; Teratocyte effect on lepidopteran host development & ecdysteroid production; LEPIDOPTERAN-HOSTS; Heliothis virescens; Parasite teratocytes effects on host development & ecdysteroid production Teratocytes deriving from the serosal membrane of Cardiochiles nigriceps Viereck, obtained "in vitro" from embryos hatched on a semidefined medium, were injected at different numbers and in different developmental stages of nonparasitized Heliothis virescens (F.) last instar larvae. Host development was affected by teratocyte injections and the responses registered ranged from normal to complete inhibition of pupation, according to the number of teratocytes injected and the developmental stage of the larva at time of injection. Complete pupation failure was observed when teratocytes derived from 4 C. nigriceps embryos were injected into 1st day 5th instar (new-slender stage) host larvae. Complete pupation occurred when teratocytes from 2 embryos were injected into 3rd or 4th day 5th instars (burrow-digging or day 1 cell formation stage). Intermediate responses, such as the formation of pupal cuticle without ecdysis or with only partial ecdysis, were obtained with intermediate teratocyte numbers, or host developmental stages. All pupae derived from teratocyte injected larvae failed to develop into adults normally obtained from control injected larvae. The larval weight just before pupation was negatively affected only when teratocyte injections were performed on 1st day 5th instar H. virescens larvae. Teratocyte injections altered the hemolymph protein titer to a level similar to that occurring in parasitized larvae. At the same time the ecdysteroid titer was characterized by a late significant increase, which reached values almost 3 times greater than found in normally parasitized larvae, and also surpassed the highest values registered for nonparasitized larvae. Ligation of parasitized larvae between the meso- and metathorax demonstrated that when the prothoracic glands were excluded, there was almost no ecdysteroid production.