The cactus moth, Cactoblastis cactorum (Berg) (Lepidoptera: Pyralidae), is an invasive species in North America, where it poses a threat to species of Opuntia Mill. of economic and ecological importance. The parasitoid Apanteles opuntiarum Martinez & Berta (Hymenoptera: Braconidae) is currently under evaluation as a potential biological control agent. This study was conducted to develop a parasitoid rearing protocol, with special attention to laboratory sex ratio and the effects of inbreeding. The parasitoid rearing method used a natural cactus host diet for culture of the moths. Female wasps were mated with siblings, non-siblings, or a combination. Clutch size, clutch number, and offspring sex ratios were recorded. The effects of sibling mating on these factors were analyzed. Offspring of sibling-mated parasitoids exhibited a significant increase in female sex ratio. The rearing method produced 6 successive generations in captivity with no additional introductions of genetic material. Hence, the protocol appears suitable for long-term maintenance of quarantine colonies. The effects of inbreeding suggest that natural populations of A. opuntiarum are subject to local mate competition. Therefore, some amount of inbreeding is recommended for maintenance of an optimal sex ratio of A. opuntiarum in laboratory colonies.