Mutant Cockroaches Learn to Avoid Sugar to Outsmart Traps

Roaches that have been hard to exterminate may be a variety that have decided sugar doesn’t taste quite so sweet as bait anymore, researchers found.

Most cockroach baits cover poison in a layer of glucose, a sugar. Some mutant German roaches, the most common species of pest found in houses, apartments, restaurants and hotels, now taste glucose as bitter, researchers said in a study released in the journal Science. This change in palate enables them to avoid traps.

The scientists collected 19 roach populations, mostly from the U.S. and Puerto Rico, to look at how common the glucose-spurning had become. They found seven populations that had the taste trait, said Coby Schal, a study author and a professor of entomology at North Carolina State University in Raleigh. He expects the numbers would have been higher had his group asked exterminators to send sample roaches from infestations that had been difficult to control by ordinary means.

“It’s very important, in terms of effective pest control,” Schal said in a telephone interview. “It’s not trivial. It’s out there.”

Glucose is a popular ingredient in poisonous baits, the researchers wrote in the study released yesterday. In normal German cockroaches, the glucose creates responses in the sugar neurons. In the mutant roaches, the glucose triggers the bitter taste bud receptors, prompting the animals to avoid the sugar.

The mutant roaches didn’t stay away from all sugars. They will still eat fructose. And they paid a price for their modified diet: they grew more slowly than glucose-chomping brethren.

More Expensive

Using fructose as a bait has drawbacks. Regular high-fructose corn syrup is 40 to 50 percent glucose, Schal said. Refined high-fructose corn syrup, which is 90 percent fructose, is more expensive, he said.

Other foods cockroaches like, such as tuna fish, can be substituted for glucose as a bait to combat the mutant taste populations. The trade off is the smell of tuna in the house, Schal said.

“It’s always a compromise in formulating baits,” he said.

Peanut butter has served as a good short-term bait solution, as roaches are attracted to the food and it doesn’t require glucose to be effective, he said.