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

Satoshi Hiroyoshi,Gadi V P Reddy,Tomoko Ganaha-Kikumura,Takayuki Mitsunaga

doi:10.3390/insects12070642

Abstract

Simple SummaryWe investigated male sperm storage in the desert locust Schistocerca gregaria. Phase (solitary or gregarious) did not affect sperm distribution in the vas deferens and seminal vesicle, whereas sperm accumulation of the seminal vesicle in gregarious locusts was promoted more than in solitary ones. Pheromones received from neither mature adults nor nymphs affected sperm distribution in the vas deferens and seminal vesicle. However, sperm accumulation in the seminal vesicle was more promoted in the gregarious locusts which received pheromones from mature adults than those obtained from nymphs at early adult stage, especially seven days after adult emergence.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.

Highlights

The desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), distributed from Africa to parts of western Asia, is a notorious pest, associated with human famines
Sperm were found in the vasa deferentia or the seminal vesicles of gregarious male locusts five days or three days after adult emergence; in some individuals kept at 30 ◦C, there were no sperm in either the vasa deferentia nor the seminal vesicles seven days after adult emergence
The amount of sperm in the vas deferens seemed to increase with sexual maturation, but the accumulation rate was not quantified in this study

Summary

Introduction

The desert locust, Schistocerca gregaria (Forskål) (Orthoptera: Acrididae), distributed from Africa to parts of western Asia, is a notorious pest, associated with human famines This locust has phase variation associated with group behavior changes and long-distance migration [1,2,3,4,5,6,7]. Nymphal pheromones delay the reproductive development of immature adults of both sexes, with adult males requiring almost one month of sexual development before mating [27,37,38,43] These two pheromones are called maturation accelerating and maturation retarding pheromones, respectively [6]. The sperm supply system, which consists of spermatogenesis, sperm storage, and ejaculation, is modulated in desert locusts, and how male sperm storage changes due to pheromones and phase variation are unclear

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