| The German cockroach, Blattella germanica, is one of the most common urban pest cockroach species. According to historical records and taxonomic studies, the German cockroach likely originated from its close relative the Asian cockroach, Blattella asahinai. The German cockroach was introduced into Europe before the 18th century and then spread to the rest of the world. The spread of the German cockroach was relatively recent compare to other pest cockroach species, for example, the American and Oriental cockroaches. Recently spread may reflected the physiological and behavior characters of the German cockroach. Previous population genetics studies discovered that the population structure of German cockroach was that of an invasive species, and its spread likely followed the process of biological invasion. Prior studies suggested complicated genetic structure and spread pattern but failed to link those patterns with biological invasion scenarios, so the origin and spread of the German cockroach remained to be discovered. Intergrating prior knowledge, I hypothesized that the German cockroach originated in South Asia, and was then introduced to Europe. Europe, where the German cockroach accomplished "domestication process", was the "bridgehead" of the worldwide spread of German cockroaches. Taking into account the adaptability and rapid local growth rate of the German cockroach, the "bridgehead effect" had the strongest influence on regional spread as compares to other invasion scenarios. The improvement of indoor environment and transportation, especially implementation of heating systems, contributed to the recent spread of the German cockroach. |
