Bugs' changing tastes pass to offspring, making them harder to bait in traps

Households in the capital will soon be on the front line of a campaign to tackle a creature that can trace its lineage back 300 million years, said Zeng Xiaopeng, deputy director of the city's disease control and prevention center.

The humble cockroach may seem an unlikely target for such a mass campaign, set to be launched in September, but its evolutionary talents have seen it acquire one of the keenest survival instincts of any living creature, including being able to cope with many pesticides, said Zeng, often described as "the cockroach expert".

Strange as it may seem, the dominant species in the capital is the German cockroach, and they have developed a pesticide resistance.

Under the campaign, "all willing households" will place specially designed traps with poison-laced bait at strategic locations, such as in kitchens and behind cupboards.

A similar campaign was conducted in 2009 and met with success as the number of households suffering from the insects' presence dropped from 40 percent to 15 percent. About 1.56 million households participated in that campaign, Zeng said.

But cockroaches can adapt quickly, and many communities have said they have noticed the creatures are returning.

Research findings published in May in Science magazine of the American Association for the Advancement of Science seem to confirm that the German cockroach can swiftly change its dietary habits.

A glucose-laced poisonous bait no longer seems to attract them, the research revealed. Researchers found that some cockroaches had developed an aversion to glucose - the sugary bait disguising the poison - and that the insects were passing that trait on to their young, the magazine said.

Cockroaches, like other insects, detect taste through receptors that line hairlike appendages on their mouthparts.

The receptors differentiate between sweet and bitter flavors, which signal to the roach whether to eat or avoid the food, the researchers said.

"We are designing an experiment to select the most effective combination of pesticide for this year's campaign," Zeng said. "We will find out what kinds of sugar are contained in the cockroach baits sold in Beijing."

Cockroaches are not the first species to be targeted.

In earlier campaigns decades ago, flies, rats and mosquitoes were successfully targeted.

"But cockroaches are tough, and an ever-changing approach has to be adopted to counteract their resistance," Zeng said.

During the 2009 campaign, the government dispatched specialists to communities. Community service centers were also given supplies of cockroach traps to be sold cheaply to residents, which led directly to the sharp drop in households reporting the insects, Zeng said.

"Yet our city monitoring teams have found that they are re-emerging. In September, more than 21 percent of households being monitored reported them. In October, the rate was more than 26 percent. The figure further rose to 34.82 percent in November."

Fu Luzhen, a community worker in a neighborhood of more than 1,500 households in Chaoyang district, said she has seen a similar trend, and residents there need another citywide campaign as soon as possible.

"The campaign in 2009 was successful. But at the end of last summer many people came to me asking if the center still offered pesticides and traps as it did in 2009. The pesticides they bought in supermarkets didn't work well," she said.

Contact the writers at shanjuan@chinadaily.com.cn and wangqingyun@chinadaily.com.cn