Transfer, subsequent movement, and fate of sperm in the tobacco hornworm moth, Manduca sexta

During mating in the Lepidoptera (moths and butterflies), sperm are passed to the female via a copulation in which the male transfers a large and often complex spermatophore over the major part of an hour or more. Subsequently, over the course of an hour or often considerably more, the sperm exit the spermatophore and travel over a relatively complex route to the spermatheca, where the sperm are stored and then used as the eggs are laid. The process of spermatophore formation and migration of sperm in the female has been described in many Lepidoptera, but the mechanics involved have received less attention. Understanding these is important in discerning the relative roles of males and females in determining the outcome of matings. We describe how the spermatophore is formed, how the sperm migrate in the female, and the fate of the sperm in the spermatheca of the tobacco hornworm moth, Manduca sexta. We found that sperm movement from the spermatophore relied upon motility of the sperm, but further movement of the sperm to the spermatheca was dependent on female muscular action. After arriving in the spermatheca, the anucleate parasperm (apyrene sperm) separated into the lateral pouch of the spermatheca (lagena) and disappeared over 7 days, whereas the eusperm (eupyrene sperm) persisted in the central lumen of the spermatheca (utriculus). The relative persistence of these two sperm types could shed some light on what determines the proclivity of females to remate. Elucidation of these physiological mechanisms contributes to an understanding of the mechanisms of female choice and male competition in Lepidoptera.