Cockroaches quickly lose sweet tooth to survive


This image made from video provided by Ayako Wada-Katsumata shows glucose-averse German cockroaches avoiding a dab of jelly, which contains glucose, and favoring the peanut butter. For 30 years, people have been getting rid of cockroaches by setting out sweet-tasting bait mixed with poison. But in the early 1990s, a formerly effective product stopped working. Some cockroaches had lost their sweet tooth, rejecting the corn syrup meant to attract them. Later studies showed they were specifically turned off by the sugar glucose in the syrup. Scientists reported Thursday, May 23, 2013 that the key is an altered behavior of certain nerves that signal the brain about foods. (AP Photo/Ayako Wada-Katsumata)

Published: Thursday, May 23, 2013 at 02:15 PM.




"Cockroaches are highly adaptive, and they're doing pretty well in the arms race with us," said North Carolina State University entomologist Jules Silverman, discoverer of the glucose aversion in that Florida kitchen during a bait test.



The key is certain neurons that signal the brain about foods.

In normal cockroaches, glucose excites neurons that tell the brain "Sweet!" In the mutant insects, glucose activates neurons that say "Sweet!" and ones that say "Yuck!" The "Yuck!" neurons dampen the signal from the others, so the brain gets the message the taste is awful. This unusual nerve activity appeared in glucose-hating cockroaches collected from Puerto Rico as well as descendants of the Florida insects.


The new work is nifty science. But does it explain why you can't get rid of the little buggers in your kitchen?

Probably not, said Coby Schal, another study author at North Carolina State.

Tests show that the glucose-hating cockroaches are happy to eat most types of bait these days, suggesting that manufacturers have removed the glucose or masked it, he said. (Bait ingredients are a trade secret.) What's more, the researchers found glucose-hating cockroaches in only seven of 19 populations they sampled from various locations.

Frankly, if the bait you put out isn't working, it's probably because you're using it incorrectly, suggested Schal, who said he consults to the pesticide industry free of charge.

Still, he said, the new work has potential to help many consumers. By studying how cockroaches evolve to evade our poisons, scientists may find clues to designing bait that the pests cannot resist.

It's not clear when the Florida cockroaches first encountered bait with glucose or how quickly they ditched their taste for the sugar, he said. But he said it's reasonable to estimate that it took maybe only five years for that glucose aversion to spread to so many cockroaches that the bait was no longer effective. That's about 25 generations of German cockroaches, which can reproduce about one to three months after they're born, Schal said.

The glucose aversion may have arisen in an individual cockroach in response to bait. Or it may have already been present in just a few individuals when the arrival of the bait suddenly gave them an advantage for surviving and reproducing. Their offspring would inherit the trait and increasingly replace other cockroaches.

Michael Scharf, an entomologist at Purdue University who studies urban pests but wasn't involved in the new work, noted that since the 1950s, cockroaches have shown they can also evolve resistance to insecticides. He agreed the latest results should help scientists develop better products to control roaches.


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