Effects of Age, Phase Variation and Pheromones on Male Sperm Storage in the Desert Locust, Schistocerca gregaria

Abstract

In general, sperm produced in the testis are moved into the seminal vesicle via the vas deferens in insects, where they are stored. How this sperm movement is controlled is less well understood in locusts or grasshoppers. In this study, the effects of age, phase variation and pheromones on male sperm storage were investigated in the desert locust, Schistocerca gregaria (Forskål). In this locust, a pair of ducts, the vasa deferentia, connect the testes to a pair of the long, slender seminal vesicles that are folded approximately thirty times, and where the sperm are stored. We found that phase variation affected the level of sperm storage in the seminal vesicle. Moreover, adult males that detected pheromones emitted by mature adult males showed enhanced sperm storage compared with males that received the pheromones emitted from nymphs: The former, adult male pheromones are known to promote sexual maturation of immature adults of both sexes, whereas the latter, nymphal pheromones delay sexual maturation. Most mature adult males had much sperm in the vasa deferentia at all times examined, suggesting daily sperm movement from the testes to the seminal vesicles via the vasa deferentia. As adult males aged, sperm were accumulated from the proximal part to the distal end of the seminal vesicle. Many sperm remained in the seminal vesicle after mating. These results suggest that young or new sperm located near the proximal part of the seminal vesicle could be used for mating, whereas old sperm not used for mating are stored in the distal part of the seminal vesicle.

The association of the development of the internal reproductive organs of male desert locusts, Schistocerca gregaria (Orthoptera: Acrididae), with age, phase and the effect of exposure to pheromones

“…In other words, solitary locusts may appear to mature sexually faster in terms of the development of male internal reproductive organs than gregarious ones. However, sperm accumulation in the seminal vesicle of gregarious locusts occurs earlier than in solitary locusts (Hiroyoshi et al, 2021a). In general, under laboratory conditions, gregarious locusts mate earlier than the solitary ones (Norris, 1954), and thus the present results are somewhat diffi cult to understand.…”

“…The testicular follicular cells that make up the testis also continued to grow in adulthood. This is strongly supported by the fact that spermiogenesis is initiated and mainly occurs shortly after the onset of adulthood (Hamilton, 1936;Hiroyoshi et al, 2021a). In Lepidoptera, where spermatogenesis is not active during the adult stage, testis size decreases from the middle or late pupal stage to the adult stage (Omura, 1936;Chandhury & Raun, 1966;Chase & Gillilalnd Jr., 1972;Scheepens & Wysoki, 1985;Sridevi et al, 1989;Hoque, 1992;Hiroyoshi, 2000;Hiroyoshi et al, 2021b).…”

“…The internal reproductive system of male desert locusts consists of a large testis, a pair of vasa deferentia, a pair of accessory glands, a pair of seminal vesicles, and an ejaculatory duct. The accessory glands each consist of 15 glands and a seminal vesicle, which is long and slender and folded approximately 30 times (Hiroyoshi et al, 2021a). The size of each reproductive organ and tissue was measured as follows.…”

“…On the other hand, in some Coleoptera, Diptera, and Hemiptera, in which spermatogenesis occurs during the adult stage, testis size increases intially and then remains constant (Nilakhe & Earle, 1976;Kotaki & Yagi, 1989;Hiroyoshi & Moriya, 1999;Hiroyoshi et al, 2016) or continues to increase with age (Ascerno et al, 1978;Ward & Simmons, 1991). In the desert locust, it is reported that sperm moves from the testis to the seminal vesicles via the vasa deferentia for at least four weeks after onset of adulthood (Hiroyoshi et al, 2021a). Therefore, the development of accessory glands, seminal vesicles, and testis in this locust could be closely associated with sexual maturity.…”

“…Thus, it is well studied. For example, male reproduction in this locust has been examined in terms of mating and sexual behaviour (Pener, 1967;Inayatullah et al, 1994;Seidelmann & Ferenz, 2002;Golov et al, 2018), testis development (Tobback et al, 2011, van Wielendaele et al, 2013, sperm storage (Norris, 1954;Hiroyoshi et al, 2021a), spermatogenesis (Das et al, 1965;Cantacuzène et al, 1972;Coggins, 1973;Jones, 1978;Bakr et al, 2010), sperm transfer (Pickford & Padgham, 1973;Boerjan et al, 2012;Dushimirimana et al, 2012) and accessory glands (Odhiambo, 1969(Odhiambo, , 1970Avruch & exposed to fi ve mature (yellow) gregarious virgin adult males or fi ve male gregarious nymphs (4 th or 5 th ) (referred to as donors) in two-chamber aluminum cages (15.5 cm × 15.5 cm × 31 cm height) with a sliding glass front at 32 ± 2°C, which allowed the insects to smell the donors (no visual or tactile contact possible). The donors were kept in the top part of the cage and, the recipients in the bottom part so that they could more easily perceive the volatiles emitted by the locusts in the upper chamber.…”