The Regulation of Spermatogenesis in Insects

The process of gametogenesis in the male insect has received far less atten­ tion than the similar event in the female. There are several reasons why this is so: the female is generally considered far more important from a point of view of reproductive strategies and has served as the focus of biological and chemical control research. The final steps in egg maturation, particu­ larly vitellogenesis, occur in the adult, are impressive from a structural point of view, and are closely regulated by hormonal systems. The male, by contrast, obeys his biological imperative by disseminating the genetic mes­ sage far and wide and as often as possible. Mature sperm usually are present at the time of adult emergence, and no obvious regulation of continued sperm production can be seen at this stage. Nonetheless, the formation of a mature spermatozoon is probably no less complex a developmental pro­ cess than the formation of a mature egg. The complete sequence of events encompasses production of primary spermatogonia by stem-cell division, sequential differentiation of secondary spermatogonia during the course of a species-specific number of incompletely cytokinetic cell divisions culmi­ nating in the primary spermatocyte, prophase maturation and the ensuing meiotic divisions, and the extensive morphological alteration of the sperma­ tid, termed spermiogenesis, by which the mature sperm is formed. Addi­ tionally, continued development outside of the male reproductive tract occurs in some, possibly most, insects. Several of these aspects of male gamete formation have been recently reviewed: stem-cell mechanisms by Hannah-Alava (62); light microscope cytology by Nath (102), ultrastructure by Phillips (112), relation of struc­ tural and somatic development to spermatogenesis by Roosen-Runge (124),