Comparative morphology of male genitalic structures in the minute litter bugs Dipsocoromorpha (Insecta: Hemiptera: Heteroptera)

Abstract

Insect male genitalia show an evolutionarily variable morphology that has proven to be valuable for both, species identifications and phylogenetic analyses at higher taxonomic levels. Accurate usage of genitalic characters in taxonomic descriptions and phylogenetic analyses depends on consistency of terminology and validity of homology hypotheses. Both areas are underdeveloped in many insect groups. We here document the morphology and advance homology hypotheses of male genitalic features for the hemipteran infraorder Dipsocoromorpha, the minute litter bugs. Genitalic structures and the pregenital abdomen in Dipsocoromorpha are strikingly modified and diverse compared to other Heteroptera. In addition to variation in the shape of phallic structures (parameres and aedeagus), minute litter bug genitalia vary in the direction and degree of asymmetry and feature a plethora of processes derived from various abdominal segments with significant variation at low taxonomic levels. Here, male genitalic structures for an extensive taxonomic sample (32 genera and 71 specimens) are documented using scanning electron and confocal microscopy, and a universal terminology for genitalic structures across minute litter bugs is established that will facilitate species discovery and evolutionary research. We conclude by proposing primary homology hypotheses across the infraorder that now can be tested in a phylogenetic framework.

Synopsis of Schizopteridae (Hemiptera, Heteroptera, Dipsocoromorpha) from the United States, with description of seven new species from the US and Mexico

“…We here introduce a slightly modified terminology for wing veins in Hypselosomatinae from those in Hill (2013) and Hoey-Chamberlain and Weirauch (2016) that also differs from the terminology used for Schizopterinae in Weirauch and Frankenberg (2015) and Leon and Weirauch (2016a,b), but is largely consistent with the terminology for Ogeriinae used by Knyshov et al (2016). The wing vein terminology is illustrated in Figure 2 for Hypselosomatinae and in Figs 6, 8 for Schizopterinae.…”

“…Here we use the terms “tergum” and “sternum” for all dorsal and ventral abdominal sclerites and “laterotergite” for a lateral subdivision of the tergum following recent papers on the morphology of the pregenital abdomen in Dipsocoromorpha (Knyshov et al 2018) and a putatively closely related group of Heteroptera (Davranoglou et al 2017). …”

“…We follow the genitalic terminology used in recent publications (e.g., Hoey-Chamberlain and Weirauch 2016; Knyshov et al 2016, 2018; Leon and Weirauch 2016a, b). …”

“…The genus Corixidea is a part of the Corixidea genus group, informally created by Emsley (1969), which also includes Hoplonannus McAtee & Malloch, 1925, Membracioides McAtee & Malloch, 1925, Oncerodes Uhler, 1894, Voccoroda Wygodzinsky, 1950, and Voragocoris Weirauch, 2012. Monophyly of the group is supported by the blunt labium, absence of a pronotal collar, venational similarities, and by limited molecular data when representatives of three genera were analyzed (Knyshov et al 2016). However, generic limits that were proposed based on morphological features are unclear when undescribed diversity of the group and the poorly described original species are considered.…”

“…Although several species occur in temperate regions in Japan, Tasmania, and New Zealand, the great majority of species have been described from wet tropical and subtropical areas around the globe (Emsley 1969, Knyshov et al 2016, Wygodzinsky 1951). The fauna of Schizopteridae in the United States could therefore be expected to be relatively small.…”