Scientists solve 250-year-old mystery of German cockroaches

A scientist from The University of Western Australia has helped solve a 250-year-old mystery, the origin of one of the most common insects found in cities around the world, the so-called ‘German’ cockroach.

Associate Professor Theo Evans, from UWA’s School of Biological Sciences, was co-author of the study published in Proceedings of the National Academy of Sciences.

“Despite its name, Blattella germanica did not originate in Germany; the famous Swedish biologist Carl Linnaeus named the species after the area where specimens were collected,” Associate Professor Evans said.

“And there are no known natural wild populations of this cockroach, so it is fully domesticated.”

Researchers sequenced the “barcode” gene CO1 of the German cockroach and compared the sequences with an anatomically similar species from Asia.

“We found that the sequence for the German cockroach was almost identical to that of Blattella asahinai, a species native to the Bay of Bengal, from east India to Bangladesh and into Myanmar,” Associate Professor Evans said.

To discover how the cockroaches spread from the Bay of Bengal to Europe researchers identified over 150,000 single nucleotide polymorphisms in DNA from cockroaches collected in 17 countries across six continents, and modelled how this variation could have appeared.

“We found an early spread route around 1,200 years ago, which was from eastern India westwards, likely from increasing trade and military activities of the Islamic Umayyad or Abbasid Caliphates,” Associate Professor Evans said.

“The next spread route was eastwards around 390 years ago into the Indonesia archipelago, likely facilitated by various European East India Companies. These companies traded spices, tea, cotton and other products within South and Southeast Asia, and back to Europe.

“We estimated that German cockroaches arrived in Europe about 270 years ago, which matches the historical records from the Seven Years’ War. From Europe the German cockroach spread to the rest of the world, around 120 years ago, probably from faster transportation on steam ships.”

Researchers concluded the rise of human civilisation triggered the evolution and spread of this now abundant species which has adapted to urban environments.

“To survive, cockroaches have to avoid being seen by humans and German cockroaches have evolved to be nocturnal, avoid open spaces, and although it retained its wings it has stopped flying,” Associate Professor Evans said.

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