Using genetics to identify the origin and the global path of the ubiquitous insect pest, the German cockroach, back to its wild origin could help us develop more effective pesticides to control them.
German cockroaches (Blattella germanica) have a high reproductive rate. (Credit: Matt Bertone and … [+]
The origin of the German cockroach, Blattella germanica, has baffled people for hundreds of years because it is ubiquitous globally in urban areas but absent from any natural habitats anywhere in the world. Further complicating matters, it was given a variety of names, depending upon people’s biases. For example, the Russians called it the “Prussian cockroach,” whilst British and Prussian soldiers knew it as the “Russian cockroach.”
“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,” the study’s senior author, evolutionary entomologist Theo Evans, an Associate Professor in the School of Biological Sciences at the University of Western Australia, said in a statement. Professor Evans is recognised as a global expert with extensive experience in behavior, ecology and evolution of invertebrate species mostly living in terrestrial habitats.
“And there are no known natural wild populations of this cockroach, so it is fully domesticated.”
But despite hundreds of years of speculation, no one could point to where this species actually did come from. But finding its original home could be helpful to dealing with this insect pest, and possibly for developing effective insecticides.
“If we can know the origin of the species, we can try to identify the mechanism of this rapid evolution of insecticide resistance,” said the study’s lead author, entomologist Qian Tang, a research associate at Harvard University.
To answer this question, Professor Evans, Dr Tang and collaborators collected samples from 281 German cockroaches from 57 sites in 17 countries. These donor cockroaches represented thousands of years of cockroach history across all six human-inhabited continents.
Professor Evans, Dr Tang and collaborators then sequenced the mitochondrial “barcode” COI gene from 53 individual cockroaches and three other Blattella species to create a haplotype network (Figure 1A). Genomic studies also revealed over 150,000 single nucleotide polymorphisms (SNPs, pronounced “snips”) that were used to reconstruct the global spread of the German cockroach (Figure 1C).
F I G U R E 1 : Population genetic structure and global spread routes of the German cockroach, … [+]
The first thing Professor Evans, Dr Tang and collaborators learned from their analysis and modelling was the so-called German cockroach is not German at all. Instead, they confirmed long-standing suspicions that this cockroach actually originated in southeast Asia, apparently evolving “from the Asian cockroach, Blattella asahinai, approximately 2,100 ya [years ago], probably by adapting to human settlements in India or Myanmar.”
Interestingly, almost 200 years ago, Charles Darwin alluded to his (correct, as it turned out) suspicion of the German cockroach’s wild origin when he mentioned the ‘small Asiatic cockroach’ in his 1859 classic On the Origin of Species.
In fact, the German cockroach’s relatives, which are very similar, physically and genetically, still live in the wild in Asia.
“We found that the sequence for the German cockroach was almost identical to that of B. asahinai, a species native to the Bay of Bengal, from east India to Bangladesh and into Myanmar,” Professor Evans elaborated.
How did the German cockroach become the most ubiquitous of urban pests? Genomic analyses revealed that they followed two routes: the first route led to West Asia, some 1,200 years ago, probably riding in soldiers’ breadbaskets.
“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,” Professor Evans explained.
Travel along the second route occurred around 390 years ago.
“The next spread route was eastwards around 390 years ago into the Indonesia archipelago, likely facilitated by various European East India Companies,” Professor Evans continued. “These companies traded spices, tea, cotton and other products within South and Southeast Asia, and back to Europe.”
The cockroach’s European invasion occurred later when they probably stowed away on Dutch and British East India Company trade routes, according to the genetic reconstruction and historical records.
“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.”
Not only were steam ships an efficient method for cockroaches to travel to the rest of the world, but globalisation of trade and housing, complete with heating and plumbing, facilitated the cockroach’s colonisation of the remainder of the world between the late 19th and early 20th centuries.
In the United States, the first report of the species was in New York in 1842, during the construction of the Croton Aqueduct.
“New Yorkers believed that the aqueduct brought the pest to the city, and so-called German cockroaches the Croton bugs,” Dr Tang noted in a 2018 review article.
In total, Professor Evans, Dr Tang and collaborators identified six migratory events from their DNA analyses, most of them originating from locations where human commercial activities would lead to an overlap of cockroaches from different ancestries. For example, the population in Singapore was introduced through the West route but received substantial migration from neighboring Indonesian populations (Figure 1D).
According to Professor Evans, Dr Tang and collaborators, the German cockroach “is the world’s most prevalent cockroach pest, is ubiquitous in human buildings globally but not outdoors” and “it imposes significant social, medical, and economic costs due to prevalent insecticide resistance allowing it to outcompete ~40 known pest cockroach species in buildings.”
Furthermore, cockroaches can trigger severe allergic reactions in people and can harbor and spread many foodborne microbial pathogens, including bacteria, viruses and parasites. Thus, cockroaches may play a wide range of roles in the spread of foodborne infections, particularly sapovirus and E. coli., according to a recent study from China. Sapovirus is most common cause of acute gastroenteritis in both humans and animals.
Unfortunately for us, modern domesticated cockroaches are a product of living exclusively alongside humans in our dwellings and eating our food for several thousand years. And, as you might expect, cockroaches evolve quickly to resist pesticides — often within a few years, according to Dr Tang.
“The German cockroach will continue to evolve and adapt to stay alive, so the arms race between us and the cockroach will go on for years to come.”
Source:
Qian Tang, Edward L. Vargo, Intan Ahmad, Hong Jiang, Zuzana Kotyková Varadínová, Pilot Dovih, Dongmin Kim, Thomas Bourguignon, Warren Booth, Coby Schal, Dmitry V. Mukha, Frank E. Rheindt and Theodore A. Evans (2024). Solving the 250-year-old mystery of the origin and global spread of the German cockroach, Blattella germanica, Proceedings of the National Academy of Sciences 121(22): e2401185121 | doi:10.1073/pnas.2401185121
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