Morphology of the Male Reproductive Tract of Mature Larval, Pupal, and Adult Tobacco Hornworms (Lepidoptera: Sphingidae), Manduca sexta1

Abstract

The male reproductive tract of Manduca sexta (L.) undergoes substantial change from the last instar to the adult. In larvae the testes are small, paired, and connected to the genital disc by paired vasa deferentia, the only larval ducts. In imagines there is a single, large spherical testis whose ducts fill much of the abdominal cavity. Morphogenetic changes of the testes include volume, tracheation, fusion, and torsion. Fusion occurs in prepupae and torsion begins three or four days after pupation. All ducts but the vasa deferentia develop from the genital disc and differentiate during prepupal and pupal stages. Rudimentary accessory glands are first visible in prepupae. After pupation, the following changes occur: the simplex and duplex appear at three or four days, the elbow of the cuticular simplex begins differentiation at five or six days, seminal vesicles of the vasa deferentia begin to differentiate at six or seven days, and secretions first appear in the lower primary simplex at nine days, in the upper vasa deferentia at 11 days, in the proximal accessory glands at 12 or 13 days, and in the duplex at 14 or 15 days. Further morphogenesis of the vasa deferentia and lower reproductive ducts include increases in length and width in pupae. Criteria for defining developmental stages of M. sexta are presented and are used to correlate development of the reproductive tract with external features of the insect.