Bacteriocytes and Endosymbionts of the German Cockroach , the Forest Cockroach , and Other Cockroach Species.

Cockroaches are commonly found in human residences and notorious as hygienic and nuisance pests. Notably, however, no more than 30 cockroach species are regarded as pests, while the majority of 4,500 cockroaches in the world are living in forest environments with little relevance to human life. Why some cockroaches have exceptionally adapted to anthropic environments and established pest status is of interest. Here we investigated the German cockroach , which is a cosmopolitan pest species, and the forest cockroach , which is a wild species closely related to . In contrast to easy rearing of , laboratory rearing of was challenging-several trials enabled us to keep the insects for up to three months. We particularly focused on the distribution patterns of specialized cells, bacteriocytes, for harboring endosymbiotic , which has been suggested to contribute to host's nitrogen metabolism and recycling, during the postembryonic development of the insects. The bacteriocytes were consistently localized to visceral fat bodies filling the abdominal body cavity, where a number of single bacteriocytes were scattered among the adipocytes, throughout the developmental stages in both females and males. The distribution patterns of the bacteriocytes were quite similar between and , and also among other diverse cockroach species, plausibly reflecting the highly conserved cockroach- symbiotic association over evolutionary time. Our study lays a foundation to experimentally investigate the origin and the processes of urban pest evolution, on account of possible involvement of microbial associates.