Factors produced in Hymenopteran parasitoids from their poison gland or from calyx region of the ovary or from both effect changes in host growth. In this review, the sources of these factors from parasitoids of Heliothis spp. (Lepidoptera: Noctuidae) are described and their effects on host growth are compared. An evaluation of protein, amino nitrogen, and trehalose levels in the hemolymph of parasitized Heliothis indicates that each parasitoid species exerts a different effect on Heliothis. A number of parasitoid genera still remain to be evaluated relative to their effects on host growth before a relationship can be established between parasitoid taxon and effects of their parasitism on hosts.