Studies on the role and regulation of the male accessory reproductive gland secretions of the cotton stainer,dysdercus fasciatus signoret (heteroptera: pyrrhocoridae)
It has been established that in most insects, reproduction is under the influence of hormones produced by the neuroendocrine system. The mechanism of such influence, particularly its role in the regulation of the male accessory reproductive glands (ARGs) of the cotton stainers, is not well understood. In the male cotton stainer Oysdercus fasciatus Signoret, the activities of the corpus allatum (CA) and ARGs were studied morphometrically and histologically to establish their possible functional relationship. Such a relationship would help to explain the unusually long copulatory phenomena characteristic of these bugs. This study was undertaken to (1) describe the activities of the CA and ARG during sexual maturation in the male O. fasciatus (2) investigate the role of the CA in the functional activities of the ARGs (3) determine the effect of the ARGs secretion on mating behaviour and sexual maturation. Results from this investigation showed that the CA and ARGs exhibited cyclic secretory activity patterns over a period of 20 days. Two peaks of maximum secretory activity in each gland lasting four days in the first cycle and two to three days in the second cycle were observed. Between these peaks there vias another synchronised period of low activity in both glands. Although the peaks of maximum secretory output (xiii) were synchronised, they were slightly out of phase with each other. The activity of the ARGs lagged slightly behind that of the CA by one day during both the first and second copulatory cycles. The attainment of maximum secretory activity by the CA on the third day coincided with the onset of copulation and release of sperm from the testes. Maximum secretory activity by the ARGs was attained on the seventh to 8th days when the insects had been in copula for about three to four days. Histological observations of the CA showed that, during the first three days following adult emergence, there was a remarkable increase in the cytoplasmic content of the CA.The size of the nuclei remained the same although in the more sexually mature insects the nuclei were slightly bigger with more visible intranuclear granules. The ARGs showed important changes in their histology during sexual maturation. At adult emergence, the epithelial cuboidal cells of the mesadenes were thick, forming sacs that contained no secretion. After the third day, there was a shrinkage in the size of the epithelia accompanied by an increase in the size of the glandular lumina, accumulation of granular secretion and increase in its staining properties. By the seventh day the glandular secretion stained very intensely and some of it could be seen in the lower part of the ejaculatory duct together with a bundle of sperm. On the ninth day, there was a reduction in size of the mesadenial lumina but the intensely stained granular secretion within was retained. (xiv) Precocene II had potent effects on the activities of CA and ARG. The response to it by the glands varied. with higher doses having greater effects than low doses. Thus applications of 1 pg/l ~l doses had no effect on the activity of the CA or ARG as indicated by the morphometric changes. Doses above 5 ~g/l ~l caused a reduction in the volume of the CA which was statistically significant (P ~ 0.05). It also retarded the development of the ARGs and delayed sperm descent by three days. Concentrations above 10 pg/l ~l led to atrophy of the CA. retarded ARG development and prevented sperm descent. Concentrations of 25 ~g/l ~l and above were lethal to the insects after the second day. Histological observations of the CA and ARG in the precocene treated insects showed that precocene acted on the CA by destroying the nuclear chromatin and synthetic machinery of the cytoplasm. The ARGs were affected by higher doses of precocene as shown by the extremely thin epithelia of the mesadenes. Time of application of the precocene was a critical factor and applications were effective only at adult emergence. The observed retarded development of the ARGs following precocene treatment indicated that the CA was involved in regulation of the ARGs. The continued secretory capability by the ARGs even at high doses of precocene suggested further that the ARGs were not exclusively under the influence of the CA. The failure of sperm to descend after (xv) precocene treatment indicated that the CA plays role in male sexual maturation. The observed earlier onset of copulation and descent of sperm from testes in newly emerged insects following the introduction of glandular homogenates of the ARGs from sexually mature male insects further suggested that the secretions of the ARGs could be playing a role in sperm maturation and translocation.