Xestoblatta, Hebard, 1916

Vélez-Bravo, Andrés & Daza, Juan M., 2021, Molecular systematics and genital morphology of the Neotropical cockroaches from the genus Xestoblatta (Blattellidae), Zootaxa 5057 (3), pp. 301-328 : 312

Morphology of Xestoblatta (sensu lato)

The high morphological variability described by Gurney (1939) for Xestoblatta , regarding the tergal modification on the abdominal segments and the branches of ulnar vein, does not correspond to intrageneric variability. Rather, such variability resulted from the indiscriminate use of traits from three unrelated lineages. From the morphological variability described above we identified three different morphological groups. These morphological groups also correspond to the three unrelated Xestoblatta lineages retrieved in our phylogeny.

Our morphological analysis show that different lineages of Blattellidae can be differentiated by the type of tergal modification in the abdomen in males. Brossut & Roth (1977) had already suggested the usefulness of this trait in cockroach taxonomy. Species of the three Xestoblatta lineages can be easily differentiated by the location on abdominal segments I, II, III or VII and by the shape of the tergal modification. On the other hand, assigning females to each lineage continues to be a challenge based only on external morphological characters, and more so in groups morphologically homogeneous as these. Tentatively, body length helps to differentiate females of lineages 2 and 3, being smaller in the latter (less than 19 mm).

Rehn (1951) considered wing venation a useful trait to discriminate groups of species in cockroaches. Similarly, Gurney (1939) based on this trait recognized two groups of Xestoblatta species , species with ulnar vein of the hind wings with up to nine branches and species with ulnar vein with more than nine branches. Our analysis showed that despite the high variability of this trait among all the reviewed species, even the intraspecific variation, two groups of species are recognized in agreement with Gurney (1939): species of lineages 1 and 2 with ulnar vein with at least eight branches while species of lineage 3 with ulnar vein with maximum of six branches. According to this, only lineage 3 can be differentiated using this trait from the other two lineages. It is still necessary to add more species in each Xestoblatta lineage to determine the potential taxonomic use of this trait, which appears to be homoplastic.

Male genitalia in cockroaches are structurally complex and, as in many other insects, are highly divergent between species ( Klass 1997). The process “via” and the sclerite R have the highest interspecific variability. The first character has unique shapes in each species and apparently there are not morphological patterns. In contrast, the sclerite R shows distinct patterns that allows differentiating the three Xestoblatta lineages. For instance, the subregions R1v and R2i and the region R3 tend to be similar in shape and/or complexity within lineage. However, morphometric studies are necessary to quantify the variation in the shapes of these genital structures and thus corroborate these the morphological patterns.