Population genetic structure in german cockroaches (blattella germanica): differentiated islands in an agricultural landscape

Although a number of species live syanthropically with humans, few rely entirely on humans for their survival and distribution. Unlike other cosmopolitan human commensals, the German cockroach (Blattella germanica), an insect of both public and livestock health concern, is considered incapable of dispersal outside human dwellings. Patterns of genetic association are therefore constrained and may not be associated with distance. Analogies with other human-commensal species are therefore impossible to draw with any degree of accuracy. In the past 2 decades, B. germanica has become a prominent pest within the US swine production system. Swine production is mainly carried out through contracted producers, each associated with a management company. It has been hypothesized that cockroach populations will be genetically structured based on association to a specific management company. Here, we tested this hypothesis using microsatellite genotypes (8 polymorphic loci) from 626 individual cockroaches collected from 22 farms in southeastern North Carolina representing 3 management companies. Significant genetic differentiation was detected (F(ST) = 0.171), most of which was partitioned among the 22 farms rather than the 3 management groups. All pair-wise population comparisons yielded F(ST) values significantly greater than zero. Our results reveal that structure does not correspond to management company of origin, but instead it may be regional and influenced strongly by the unintentional movement of cockroaches by farm workers.