How did German cockroaches invade the world?

New research traces the evolution of German cockroaches throughout human history from the Islamic empires to present-day Europe .

Despite its name, the German cockroach ( Blattella germanica ) now inhabits every continent except Antarctica. In fact, scientists consider them the most common of the 4,600 species of cockroaches on Earth. They were essentially unknown in Europe until Swedish biologist Carl Linnaeus first described them in 1767. They have no close relatives there and do not exist in the wild. . The reason they have become such a global pest lies in the German cockroach's DNA , according to research results published on January 20 in the journal Proceedings of the National Academy of Sciences .

German cockroaches spread throughout the world thanks to their adaptability and rapid reproduction rate. (Photo: Action Pest Control).

By analyzing genome-wide markers of 281 cockroaches from 17 countries on 6 continents and measuring how closely related they are, scientists have for the first time traced the process of rapid increase and expansion. of German cockroaches. All signs point to them evolving from the Asian cockroach ( Blattella asahinai ) about 2,100 years ago in present-day India and Myanmar. Bypassing their natural environment to live in the shadow of humans, German cockroaches appear to have arrived in the Middle East about 1,200 years ago, possibly due to increased trade and military campaigns in the Umayyad or Abbasid caliphates. The empire once stretched from northern Africa to Western Asia.

German cockroaches experienced another geographical leap about 390 years ago when increased colonization brought them to Europe and then the rest of the world thanks to improved transportation and trade. and indoor heating systems, which help these insects survive in cold weather. Obviously, all migrations and movements of German cockroaches are aided by humans. "German cockroaches can't even fly ," said Qian Tang, an evolutionary biologist at Harvard University who led the research team. "They follow human ships around the world."

However, the successful spread of German cockroaches is not simply due to luck. Instead, the main reason lies in their ability to adapt and evolve. That's something scientists today still seek to understand.

To get a sense of how much German cockroaches have changed over the past two millennia, the team compared them with their closest living relatives, the Asian cockroach. Although the two species are almost identical, they are very different in behavior. Asian cockroaches fly toward the light source while German cockroaches scurry away, according to Chow-Yang Lee, an urban entomologist at the University of California, Riverside. Similarly, if you throw two species into the air, the Asian cockroach will fly and the German cockroach will land on the ground and run away.

The study also revealed that the German cockroach's genome reflects its relationship with humans. For example, German cockroaches in Singapore and Australia are more closely related to their relatives in the US than German cockroach populations in Indonesia, likely because the US has more trade with Singapore and Australia than Indonesia.

German cockroaches also outcompete other cockroach species everywhere they appear , according to Tang. One reason for their success is that they reproduce faster than most other cockroach species, allowing them to quickly develop resistance to insecticides. Previous research has revealed that after years of baiting cockroaches with sugar-laced poison, the surviving population produces a new generation of cockroaches that do not eat sweets.