Beiträge zur Morphologie und Physiologie des Genitalapparates der weiblichen Lepidopteren

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

“…Ever since the first descriptions of the somewhat complicated journey of sperm inside the reproductive tract of female Lepidoptera, these reports (Michael, 1923; Weidner, 1934; Omura, 1938; Benz, 1977) have often been accompanied by suggestions of chemotaxis by sperm to the spermatheca, but this has never been verified. Using Bombyx mori , Weidner (1934) claimed chemotaxis based on simple choice experiments in which sperm accumulated in a capillary tube or a droplet containing a spermathecal gland, in preference to one without. This result could be attributable simply to a stimulation of motility, though this in itself is an interesting result.…”

“…In the basal half of the spermathecal duct leading to the vestibulum, Hewer (1934), Weidner (1934) and Omura (1938) apparently independently discovered that the duct bifurcates, forming a very narrow, pronounced, heavily chitinized channel in the wall of the main duct that spirals around the duct until it reaches the vestibulum. This has been called the ‘fertilization canal’ and several investigators assert that in various lepidopteran species, sperm do indeed travel in this groove during fertilization of the eggs prior to oviposition (Weidner, 1934; Omura, 1938; Callahan & Cascio, 1963; Miskimen et al ., 1983; Tschudi‐Rein & Benz, 1990). The latter two reports also note that during oviposition in Diatraea saccharalis and P. brassicae , a peristaltic contraction beginning in the utriculus pushes sperm into and down the spermathecal duct.…”

“…In several lepidopteran species, escape of the sperm from the spermatophore has been attributed to its mechanical rupture, such as crushing the spermatophore, breaking the spermatophore stalk, or grating the spermatophore bulb with a toothed, heavily chitinized area (‘lamina dentata’ or ‘signum’) in the bursal wall that exists in most Lepidoptera, including M. sexta (Weidner, 1934; Srivastava & Srivastava, 1957; Watanabe, 2016). But the spermatophore stalk in at least most species of Lepidoptera studied, including M. sexta , has a preformed opening at its tip, and this seems a more parsimonious way to effect escape of the sperm.…”

“…All histological studies to date in Lepidoptera have shown muscular layers around the bursa (especially at its base near the stalk), a thick layer around the seminal duct, and investments around the common oviduct and spermathecal duct leading to the spermatheca, the last having various thicknesses of muscle (Hewer, 1934; Weidner, 1934; Musgrave, 1937; Omura, 1938; Miskimen et al ., 1983). Many reports describe contractions of the bursa wall after spermatophore transfer and we observed the same for 1–2 h after the end of copulation in M. sexta .…”

“…In any case, irrespective of mating, several other organs, for example, the nerve cord and hindgut, in the abdomen of adult Lepidoptera normally contract regularly, probably as a means to promote haemolymph circulation and perhaps air circulation in the tracheal system. It has often been suggested that the bursal contractions may play a role in evacuating the spermatophore of other lepidopteran species, and may indeed do so in those species that have soft spermatophores (Norris, 1932; Hewer, 1934; Weidner, 1934; Thibout, 1977). But the experiments reported above in M. sexta , which has a relatively incompressible spermatophore, show that contractions are unlikely to be important.…”