A synopsis of the numbers of testicular follicles and ovarioles in true bugs (Heteroptera, Hemiptera) – sixty-five years of progress after J. Pendergrast’s review

Abstract

The structure of testes and ovaries can be described in its simplest form by the number of follicles and ovarioles they contain. Sixty-five years after the last review of the internal reproductive systems in true bugs (Heteroptera), the data accumulated today on the number of testicular follicles and ovarioles in their gonads are summarized. In addition, data on the number and type (mesadenia/ectadenia) of accessory glands are given. The hemipteran suborder Heteroptera constitutes one of the most diverse groups of non-homometabolous (‘Hemimetabola’) insects, comprising more than 40,000 described species worldwide and approximately 100 families, classified into seven infraorders. Data are available for all infraorders; however, more than 90% of studied species belong to the largest and most evolutionarily derived infraorders Cimicomorpha and Pentatomomorpha. In true bugs, in general, the number of follicles varies from one to nine (in a testis), and the number of ovarioles varies from two to 24 (in an ovary). Seven follicles per testis and seven ovarioles per ovary prevail being found in approximately 43.5% (307 species) and 24.4% (367 species) of studied species, respectively. Such a structure of testes and ovaries is considered an ancestral character state in the Heteroptera. In the evolution of this group, the number of follicles and ovarioles both increased and decreased, but the trend towards a decrease clearly prevailed.

Morphology of the male reproductive system and sperm of Leptoglossus zonatus (Dallas, 1852) (Heteroptera: Coreidae)

“…The number of follicles per testis can range from one to nine in Heteroptera, but it tends to be consistent in a species, genus, or even within a family (Freitas et al, 2010;Gapon et al, 2021;Grozeva et al, 2022;Karakaya et al, 2012;Matsuda, 1976;Mr oz & Wojciechowski, 2011;Özyurt et al, 2013, 2014Rezende et al, 2021). Seven follicles, as occurs in L. zonatus, have been considered the modal number for heteropteran, as it has been the most commonly observed number in the order (Freitas et al, 2010;Gomes et al, 2013;Karakaya et al, 2012;Kaur & Patial, 2012Özyurt et al, 2014Pendergrast, 1957).…”

“…The number of follicles per testis can range from one to nine in Heteroptera, but it tends to be consistent in a species, genus, or even within a family (Freitas et al, 2010; Gapon et al, 2021; Grozeva et al, 2022; Karakaya et al, 2012; Matsuda, 1976; Mróz & Wojciechowski, 2011; Özyurt et al, 2013, 2014, 2015; Rezende et al, 2021). Seven follicles, as occurs in L .…”

“…There is also an ejaculatory duct and then an ejaculatory bulb (Özyurt et al, 2013; Pendergrast, 1956, 1957). Each testis can have from one to nine follicles (Grozeva et al, 2022; Rezende et al, 2021), according to the species, and the follicles are filled with cysts, where spermatogenesis occurs (Phillips, 1970). Differences found in testes organization, such as the number of follicles per testis, can be used in systematics (Phillips, 1970; Schuh & Staler, 1995).…”