Manduca sexta; SIZE-; Food plant allelochemicals effect; FOOD-PLANTS; Plant allelochemicals, effect on hymenopteran parasite biology; DEVELOPMENT-; HYMENOPTERAN-PARASITES; Cotesia congregata; Food plant alleolchemical effects on parasite & host biology; SURVIVAL-; Rate, effects of food plant allelochemicals Cotesia congregata; SIZE-; Plant allelochemicals in lepidopteran host diet significance; DEVELOPMENT-; LEPIDOPTERAN-HOSTS; Manduca sexta; Host food plant allelochemical effects on host & parasite biology; SURVIVAL-; Rate, significance of plant allelochemicals in lepidopteran host diet Experiments were conducted to determine if three plant defenses affected the parasitoid Cotesia congregata in a fashion that would influence herbivore-parasitoid interactions. We evaluated the developmental rate, size, and survival of the parasitoid Cotesia congregata , when reared from Manduca sexta fed on diets containing either nicotine, rutin, or hordenine. These results were compared to the effects of the same three chemicals on unparasitized M. sexta . The influences of the three plant defenses differed. In general, however, the effect of these allelochemicals on the parasitoid paralleled those on the unparasitized hornworm. The one major exception was that concentrations of nicotine that had little or no effect on the hornworn caused significant mortality of parasitoids. Neither rutin nor hordenine had large or consistent negative effects, although rutin had a pronounced effect on both hornworm and parasitoid developmental times. none