The Reproductive Physiology of the Screwworm, Cochliomyia Hominivorax (Diptera: Calliphoridae). I. Oogenesis

Abstract

Oogenesis in the screwworm fly, Cochliomyia hominivorax, was divided into a series of 10 stages, where the germarium was defined as stage 1, the beginning of yolk formation as stage 4, and the mature egg as stage 10. The volume of the nurse cell nuclei was maximum at stage 6 and then started to decrease, However, maximum cytoplasmic volume of the nurse cells was observed in stage 7 follicles. The nurse cells degenerated during stage 9. Chorion formation started in stage 9 follicles and was completed by stage 10. The number of follicle cells increased during stages 2, 3, and 4 and decreased during stages 6 through 10. The follicle cells over the nurse chamber were squamous during stages 6 through 9. During stages 6 and 7, the follicle cells over the oocyte were columnar; during stage 8, they were cuboidal, and durilig stages 9 and 10, they became elongated. Parous flies could be distinguished from nulliparous flies by the presence of follicle cell residues in the ovarioles, distended ovarioles, and the absence of pupal fat body. Egg development (egg stage vs age) fit the equation L_nY = a + bX. Stages 2 and 3 lasted longer than any of the other stages. At 24°C, development of eggs to maturity took 152 h and at 30°C, it took 80 h. As long as mature eggs were present from the 1st cycle, the 2nd cycle did not develop past stage 4, and the 3rd cycle consisted of the germarium. Removal of the ring gland in flies 4 h postemergence resulted in the cessation of the 1st cycle at stage 4.