The microfilariae of 2 species of Dipetalonema (i.e., D. gracile and D. caudispina), common parasites of South American monkeys, develop to the third (infective) stage in the biting midge, Culicoides hollensis. Development of both species occurs in the abdominal fat body; D. gracile requires 13 days and D. caudispina 9 days. Despite similarities in the patterns of development of both species, the third-stage larvae of each is morphologically distinct.