Blattodea

(Cockroaches)

Donald G. Cochran

Virginia Polytechnic Institute and State University

Cockroaches are an ancient and highly successful form of insect life. They were among the groups of insects that evolved during the first great radiation of insects and have been in existence for at least 350 million years, or since early Carboniferous times. They seem to have achieved an optimum body form and other features early in their evolutionary history. Fossil specimens are relatively abundant; some that are at least 250 million years old are easily recognizable as cockroaches and could pass for modern species. Among the features that allowed them to escape the extinction that claimed many of the earlier insect groups was the ability to fold their wings over the body. This allowed them to more easily hide from predators and escape other dangers. They also evolved early in their existence an ootheca that could be hidden, hence offering some measure of protection for their eggs.

Cockroaches are referred to as generalized orthopteroid insects, which classifies them with the true Orthoptera (crickets, katydids, grasshoppers, locusts), Phasmatodea (walkingsticks), Mantodea (praying mantids), Plecoptera (stoneflies), Dermaptera (earwigs), Isoptera (termites), and a few other minor groups. The phylogenetic relationships among all these groups are not firmly established, although several theories exist. The closest relatives of cockroaches are believed to be the mantids, and some modern taxonomists prefer to place these two groups, as well as termites, in the order Dictyoptera. Indications are that termites evolved out of the cockroach stem or that cockroaches and termites both evolved from a common ancestor. One family of cockroaches (Cryptocercidae) and one extant relic species of termite (Mastotermes darwiniensis) have certain characteristics in common. Among them are the segmental origin of specific structures in the female reproductive system and that both deposit their eggs in similar blattarian-type oothecae. They also share a system of fat body endosymbiotic bacteria that is common to all cockroaches but is unique to Mastotermes among the termites.

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