Ultrastructure of posterior sternal glands of Macrotermes annandalei (Silvestri): New members of the sexual glandular set found in termites (Insecta)

Abstract

In female alates of Macrotermes annandalei, two types of abdominal glands are involved in the secretion of sex pheromone. Tergal glands are found at the anterior margin of tergites 6-10 and posterior sternal glands (PSGs) are located at the anterior margin of sternites 6-7. The cytological features of both types of glands are quite similar. The fine structural organization of PSGs is studied more precisely and described for the first time. The glandular cuticle is pitted with narrow apertures corresponding to the openings of numerous subcuticular pouches. Several Class 3 glandular units open in each pouch. One canal cell and one secretory cell make an individual glandular unit. The canal cell is enlarged apically and is connected with the other canal cells to form a common pouch. Based on the structural features found in these glands, we propose a common secretory process for PSGs and tergal glands. During the physiological maturation of alates inside the nest, secretory vesicles amass in the cytoplasm of secretory cells, while large intercellular spaces collapse the cuticular pouches. At the time of dispersal flight, pouches are filled with the content of secretory vesicles while intercellular spaces are sharply reduced. After calling behavior, no secretion remains in the glands and pouches collapse again, while secretory cells are drastically reduced in size. The structure and the secretory processes of PSGs and tergal glands are compared to those of abdominal sexual glands known in termites.

Ultrastructural study of tergal and posterior sternal glands in Prorhinotermes simplex (Isoptera: Rhinotermitidae)

“…Apart from cellular composition, the tergal and the posterior sternal glands are organised similarly to the modal situation in termites (Noirot, 1969;Ampion & Quennedey, 1981). Posterior sternal glands of different structure were found in Macrotermes annandalei (Quennedey et al, 2004).…”

“…Abdominal glands with specific sexual function occur in almost all representatives of Isoptera and Blattodea (Ampion & Quennedey, 1981;Grassé, 1982;Sreng, 1984;Quennedey et al, 2004), but evidence about their presence in Mantodea is missing. In termites, the following glands were described: sternal, posterior sternal and tergal glands (Noirot, 1969;Ampion & Quennedey, 1981;Grassé, 1982).…”

“…The sternal glands produce predominantly trail pheromones although they secrete sexual pheromones in the imagoes of certain species. The tergal and the posterior sternal glands (if present) are involved in swarming, mate attraction and courtship behaviour (Noirot, 1969;Varma, 1980;Ampion & Quennedey, 1981;Pasteels & Bordereau, 1998;Quennedey et al, 2004;Peppuy et al, 2004).…”

“…In Mastotermes darwiniensis Froggatt, the most primitive termite, eight glands (from the 3rd to the 10th tergite) are present, considered a plesiomorphic character (Ampion & Quennedey, 1981). The tergal glands occur on posterior tergites in the number from 5 to 8 in the genus Macrotermes Holmgren as an apomorphy (Ampion & Quennedey, 1981;Quennedey et al, 2004). The tergal glands are present in both sexes of primitive Isoptera, while only appearing in females in the advanced families Rhinotermitidae and Termitidae (Ampion & Quennedey, 1981).…”

“…According to observations made on females of Cornitermes bequaerti Emerson, tergal glands are composed of class 1, 2 and 3 cells (Bordereau et al, 2002). Tergal and posterior sternal glands of unique structure were found on sternites 6 and 7 in females of Macrotermes annandalei (Silvestri), formed by class 3 cells extending to subcuticular pouches (Quennedey et al, 2004).…”