Differentiation of male reproductive system inOryctes rhinoceros (Coleoptera: Scarabaeidae)

Abstract

The male reproductive system of adultOryctes rhinoceros consists of a pair of testes with 6 follicles in each, connected to vasa deferentia by small vasa efferentia, a pair of accessory glands, a median ejaculatory duct and a chitinous intromittent organ. The differentiation of these structures in the successive instars is described in detail. In the first, second and early third (final) instar larvae the reproductive system is rudimentary consisting of a pair of testes (each testis is a rounded aggregate of 6 follicles held together in a connective tissue sheath), a pair of delicate ducts or the vasa deferentia connected to ‘genital disc’ at the mid-ventral aspect of the 9th abdominal sternite. A chitinous plate makes its appearance in the ‘genital disc’ of second instar and is discarded alongwith prepupal exuvium. In the pupa, each testicular follicle gets separated to independent disc shaped organ. The ejaculatory duct and accessory glands differentiate from the distal part of ‘genital disc’ whereas the proximal part gives rise to the intromittent organ. Definitive spermatogonia differentiate in the late third instar larval testis. Spermatocysts and meiotic figures are seen only in the pupal stage and spermiogenesis after adult emergence. Sperm bundles are noticed only in a 2–4-day old adult. Accessory glands release secretion in 10–14-day old adult. Gradual degeneration of testis and ducts is observed in the adults from the third month onwards.