The mating habits of cockroaches and developmental characteristics help uncover the evolution of insects

Often associated with dirty living conditions and the spread of disease, cockroaches understandably have a bad reputation. But of the 4,600 species of cockroaches alive today, only a few are considered parasites, with most choosing to live in leaf litter, rotten trunks or caves, well away from human habitation.

Despite the discovery of fossils dating back to the Carboniferous period ~ 320 million years ago, the evolution of modern cockroaches of these prehistoric ancestors remains somewhat confusing. To better understand the relationships between modern cockroaches and potentially shed light on their evolutionary history, researchers led by Tsukuba University turned to an often overlooked group of predominantly cave-dwelling cockroaches called Nocticolidae.

“Previous work indicated that the Nocticolidae are a twin group of the Corydiidae (sand-dwelling cockroaches) and that these two families, along with the Lamproblattidae, are the most basal subgroups of the order Blattodea, which includes cockroaches and termites,” he explains. study Professor Ryuichiro Machida. ‘Interestingly, the similarities in wing design suggest that Nocticolidae species may also be the closest relatives of the extinct insect order Miomoptera, which is often believed to be the common ancestor of many today’s insects.’

Somewhat unusually, mating habits and embryonic development can be used to classify and distinguish various cockroach families. The researchers then examined the mating behavior, manipulation of the ootheca (egg sac) and embryonic development of Nocticola sp. cockroaches, which belong to the Nocticolidae family.

Publishing their findings in a recent issue of Arthropod Systematics & Phylogeny, the researchers noted that the short-winged male Nocticola sp. cockroaches quickly flapped their wings near females before entering end-to-end copulation. After copulation, the females produced an ootheca, which they carried for several days before settling on the ground. Although such a unique wing flapping behavior has not previously been observed in cockroaches, the other observed behaviors are consistent with mating and ootheca manipulation of Corydiidae species, suggesting a close evolutionary relationship.

In particular, however, symbiotic bacteria, common to other cockroach families, have not been observed in Nocticola sp. However, the shape of the egg and the embryonic development, with the orientation of the embryo remaining unchanged, in Nocticola sp. they were still consistent with Corydiidae.

“Given the consistency in mating behavior, egg structure, ootheca delivery, and embryonic development between Nocticola sp. And Corydiidae, we expect a close association between Nocticolidae and Corydiidae, supporting a shared common ancestor,” says Professor Machida. “Promoting our understanding of the phylogenetic position of Nocticolidae within Blattodea is essential for inferring the superior phylogeny and evolution of insects.”