Factors that might affect parasitism rate and progeny production of Cotesia marginiventris (Cresson), a solitary endoparasitoid of lepidopteran larvae, were considered in this study. Hosts were Spodopteraexigua (Hubner) larvae, which were feeding gregariously on artificial diet within 270-mL unicellular rearing trays. The following hypotheses were tested: (1) parasitism and superparasitism rates increased as exposure time and parasitoid density increased, and (2) progeny production decreased as parasitoid age increased. Parasitism rate increased significantly as exposure to S. exigua larvae increased from 2 to 6 h, but not from 6 to 18 h. Superparasitism rate was not affected significantly by exposure time. Both parasitism and superparasitism rates were greatest at a density of 3 rather than 1 parental parasitoid per tray; no differences were evident between densities of 3 vs 2 or 2 vs 1 parasitoid per tray. Significantly more offspring were produced (with normal sex ratios) when parental females were inserted into rearing trays as adults rather than as pupae (in cocoons). Also, 1- to 2-d-old and 8- to 9-d-old females produced more progeny (with normal sex ratios) than 15- to 16-d-old females. This study suggests that inserting a single, mated 1- to 9-d-old C. marginiventris female into a unicellular rearing tray containing an abundance of putative hosts could limit superparasitism without seriously reducing progeny production. Partial automated rearing of C. marginiventris is possible. Techniques; Care in captivity; Reproduction; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Spodoptera exigua (Noctuidae); Hymenopteran parasites; Cotesia marginiventris; Production of parasitoid in unicellular rearing trays Cotesia marginiventris (Braconidae); Rearing techniques; Production in unicellular rearing trays using lepidopteran host; Reproductive productivity; Progeny production; Lepidopteran hosts; Spodoptera exigua none