Hailed through decades — if not centuries — for being a formidable adversary, cockroaches continue to amaze entomologists and PMPs with their evolutionary prowess and overall hardiness. The latest addition to the U.S. cockroach population, the Yamato cockroach (Periplaneta japonica), also called the Japanese cockroach, is no exception. This particular pest has the ability to withstand the kind of freezing temperatures that send most pests scurrying for the nearest warm building or underground harbor.
“One of our technicians spotted the Yamato cockroach in the spring of 2012 as he was servicing rodent bait stations in an elevated walking park in Manhattan. It looked different from any roach he had seen before, so he brought some samples back to the office,” says Ken Schumann, staff entomologist and technical operations manager for Bell Environmental Services in Fairfield, N.J. “We shared several specimens with some other local entomologists who, like me, recognized the species as different but couldn’t pinpoint the taxonomy.”
The specimens made their way to the University of Florida and were examined by several other entomologists before ultimately being identified in early 2013 as the Yamato cockroach by Rutgers University Assistant Professor Jessica Ware and graduate student Dominic Evangelista. DNA barcoding confirmed the unwanted park guests were Periplaneta japonica.
“This species is closely related to the American cockroach,” explains Evangelista, “but there are recognizable differences in color, size and other characteristics. Notably, female Yamato cockroaches have much shorter wings than their male counterparts, while male and female American roaches have similarly sized wings. Yamato males are subsequently more mobile than females.”
In terms of color, Yamato roaches are black or blackish-brown rather than reddish-brown like American cockroaches. Size-wise, Yamato roaches tend to be a bit smaller, averaging 3 cm (1.2 in) in length, while American roaches grow to an average length of 4 cm (1.6 in).
Trek from Asia.
Bell’s discovery is believed to be the first documented sighting of the Yamato cockroach in the United States. The species, a primarily outdoor insect indigenous to Japan, China and southeast Russia, has been studied for decades — in its homeland.
“Although new to us, researchers in Japan have long studied Periplaneta japonica,” says Ware. “One experiment in particular tested the insect’s resistance to cold by submerging nymphs in ice for various periods of time. Within a matter of minutes from removing them from the ice, the nymphs started running around and behaving normally.” A 1997 abstract by Tanaka Kazuhiro documents this study, reporting that nymphs survived a 12-hour period of tissue freezing at temperatures of -9°C to -6°C (16°F to 21°F). Tanaka’s research also confirmed Yamato cockroaches, which have a two-year life cycle, overwinter twice as nymphs before maturing into adults.
“The temperature tolerance of this cockroach appears to be similar to that of another outdoor cockroach commonly found in the northeastern United States, the Pennsylvania woods roach (Parcoblatta pennsylvanica),” adds Schumann. “The ability of the Yamato cockroach to survive New York winters may be attributable to New York’s sharing the same geographical latitude with Japan (40°N).”
OK, so they’re comfortable here, but how did they get here? Early speculation from bystanders was, because the park in which they were found had only recently been converted into a public space, imported plants were to blame. But Schumann says that’s not the case — that his customer sourced plants from local nurseries. However, Evangelista points out, if those nurseries import any plants, there could have been cross-contamination. Mulch and soil often play a part in transporting tramp species as well. To date, however, it’s unclear how the Yamato cockroach made its entrée into New York.
Not quite sure how to approach the new Manhattan pests, the Bell team explored a variety of control options. They studied the roaches’ behaviors and discovered they had found harborage in and under manmade objects as well as within the park’s ornamental plants. Large pockets were found under removable boardwalk sections in the garden’s walking paths as well as inside rodent bait stations, electrical boxes and irrigation water valve boxes.
“We decided to apply a granular pyrethroid to identified shelter zones and planting beds that exhibited activity, and we achieved outstanding results in suppressing the population,” Schumann said. “However, the roaches rebounded quickly, and the harsh New York winter didn’t slow them down at all. We recognize that our treatments have to be able to stand up to the weather.”
Schumann said Bell recently found Yamato roaches feeding on, and dying from, baits that had been set out for other insect species. As research on the new species continues, he is confident alternative management methods will be identified.
Homes Near You?
In its native land, the Yamato cockroach has also adapted to indoor living, with populations thriving in residential and commercial dwellings. Its sightings to date in the United States, however, have been limited to the outdoors — more specifically, to a four-block area of the public park where the Bell technician first spotted the insect. Will it become an indoor menace here or remain outdoors? The bigger question: Is its presence sizable enough to be considered a menace at all? Scientists agree it’s too soon to tell.
“It’s unlikely that populations are limited to this one park, but until we do more sampling, we can’t be sure,” says Ware, whose summer plans include collecting more samples at the park to estimate population size.
For a while at least, adds Evangelista, the Yamato cockroaches will be too busy competing for food and space to focus on propagating their species. “This species is very similar to species that have already established themselves in the urban environment. They will need to compete for food and space, which leaves little time and energy for reproduction,” he says.
Michael Scharf, professor of urban entomology at Purdue University, says, “To be truly invasive, an organism needs to disrupt its ecosystem, displacing other organisms. There’s no evidence suggesting that this has happened with Yamato cockroaches. That’s not to say we should be complacent, though. It’s important for PMPs to keep their eyes open for these insects and for scientists to continue researching the populations they discover. Whether or not Yamato cockroaches become a concern to the industry remains to be seen.”
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