The staging of oogenesis in pupae and young virgin females of T. rutilus is described. Oogenesis is precocious; vitellogenesis begins in the pupal stage and some mature follicles are found as soon as 1 day after ecolosion of the adult. Terminal follicles are initiated at different times and perhaps mature at different rates. As a result, oogenesis is asynchronous in contrast with the pattern observed in other mosquitoes. A high incidence of oosorption was noted in young females but not in pupae; oosorption was not related to exhaustion of the nutrient reserves. This anomalous pattern of mosquito oogenesis is related to the peculiar life histories of the predatory Toxorhynchitinae.