Ultrastructural study of testis development and spermatogenesis in Kalotermes flavicollis (Fabr.) (Isoptera, Kalotermitidae)

Abstract

Testes of larvae, nymphs, young winged imagoes and primary reproductives of Kalotermes flavicollis (Fabr.) were examined by light and electron microscopy. They are composed of 7–8 lobes enveloped by a tri‐layered wall made up of: i) an outer monolayered cellular sheath above an acellular lamina; ii) a lacuna in which plasmatocytes and granulocytes are found; iii) a testis tunica propria. In the 3rd and 4th larval instar it is not yet possible to discriminate the somatic cells from the germ ones. In the 5th‐ instar larvae, lobes exhibit the typical organization of insect testis follicles with four, linearly arranged regions. In the germarium a group of apical cells, in close connection to predefinitive primary spermatogonia, is present. In 5th instar larvae, spermatogenesis is completed and, in the testis terminal chamber, sperms are always found. In nymphs, young winged imagoes, and primary reproductives, all regions of testis follicles appear progressively larger than 5th instar ones and cysts of germ cells arc more numerous. Germ cell ultrastructure during spermatogenesis is mostly similar to the one described for other insect species, but distinctive features of K. flavicollis, reported here for the first time, are: i) in the cytoplasm of definitive primary spermatogonia and secondary spermatogonia, the presence of a ≪cister‐nal complex≫ made up of a bunch of smooth endoplasmic reticulum cisternae, which disaggregates in primary spermatocytes; ii) the presence of microvillar expansions on the surface of secondary spermatogonia and primary spermatocytes; iii) the loss of syncytial arrangement during the first meiotic division, which is associated to the loss of synchronous development within a cyst.

Key words:

• Testis
• Spermatogenesis
• Ultrastructure
• Kalotermes flavicollis
• Termite