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Mutant Cockroaches Outsmart Traps by Rejecting Glucose [VIDEO]

May 24, 2013 11:08 AM EDT

A strain of mutant cockroach can outsmart the sugar traps used to eradicate them by essentially reprogramming their sense of what tastes the best.

Researchers from North Carolina State University have shown that a type of German cockroach is systematically rejecting glucose, a common ingredient in the poisonous roach traps used to kill the pests.

Generally, roaches prefer sugary things, but in a particular breed of German cockroach, sweet glucose sets off bitter receptors in the roaches' taste buds, causing the roaches to avoid sugary foods. Researchers say that the sugar aversion has a genetic bias and can spread through generations, which will result in an increasingly large body of cockroaches that reject glucose and any poison bait made with it.

For at least 20 years, entomologists had suspected the sugar-switch, namely because of reports that pest controllers were failing to eliminate cockroaches from properties because the insects were not taking the bait.

But the latest study on the sugar-averse roaches has revealed the neural mechanism behind the phenomenon.

"We don't know if glucose actually tastes bitter to glucose-averse roaches, but we do know that glucose triggers the bitter receptor neurons that would be triggered by caffeine or other bitter compounds," said Coby Schal, the lead author of the research.

"That causes the glucose-averse roach to close its mouth and run away from glucose in tests."

A simple taste test experiment conducted on glucose-averse roaches and normal cockroaches used peanut butter (low glucose) and strawberry jam (high glucose). Normal roaches swarmed to the sugary jam, but the glucose-averse roaches took one taste and quickly went elsewhere for food.

However, the researchers noted that the roaches do not reject all sugars, just glucose; when offered fructose, the roaches seemed happy to partake.

Elli Leadbeater from the Institute of Zoology in London, not involved in the study, told the BBC that when natural selection changes taste abilities, it usually makes animals more or less sensitive to certain taste types.

"In the cockroach case, sugar actually tastes bitter - an effective way for natural selection to quickly produce cockroaches that won't accept the sugar baits that hide poison."

Schal noted that many pest control agencies have had difficulty with pests developing a resistance to the insecticides themselves and that glucose aversion will prove an additional challenge.

"Most times, genetic changes, or mutations, cause the loss of function," Schal said. "In this case, the mutation resulted in the gain of a new function - triggering bitter receptors when glucose is introduced. This gives the cockroach a new behavior which is incredibly adaptive. These roaches just got ahead of us in the arms race."

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