Testicular maturation in the sheep bot fly Oestrus ovis

The process of testicular maturation in relation to intrapuparial developme nt was studied in the sheep nasal bot fly, Oestrus ovis L. (Diptera: Oestri dae). After formation of the puparium. during larval-pupal apolysis and the cryptocephalic pupal stage (approximate to 24-72 h), spermatogonia had und ergone mitotic divisions and sperm cysts had been formed. Five days after p upariation, spermatogonia transformed into primary spermatocytes during the phanerocephalic pupal stage, and secondary spermatocytes first appeared du ring the pupal-adult apolysis. Secondary spermatocytes began undergoing the second meiotic division by day 8 (transparent-eye pharate adult stage). By days 9 and 10, round spermatids were present and began to elongate by day 11. By day 12, the first bundles of tailed spermatozoa had appeared. By day 15 (the yellow-orange eye pharate adult stage), round, elongated, tailed a nd bundled spermatids. were predominant and by day 17 differentiating sperm atids occupied nearly 35% of the testicular cavity, and 60% was occupied by free sperm, By day 21 (the red-brown eye pharate adult stage), spermatozoa colonized the seminal vesicle. At emergence (approximate to day 22), a com plement of free sperm occupied the testis and the seminal vesicle, but grou ps of developing cells frequently remained in certain zones. Spermatogenesi s was carried out after pupariation and spermiogenesis occurred during the pharate adult stage. After emergence, males possessed fully formed spermato zoa ready for ejaculation.