Cockroaches Mutate to Find Sweet Glucose Bait Bitter

By Wesley Fenlon

Want to trap cockroaches? Just draw them in with sugar--as long as you're not in Germany, where some cockroaches have evolved a distaste for the common glucose bait.

When roaches infest your home, there are usually a few different ways to take care of them. You can run a tidy kitchen and make sure there's no food sitting out to attract them. You can have a Men in Black-style cockroach stomping party. Or you can use baited traps to lure them out.--unless they're German cockroaches, which have, apparently, evolved to find sugary glucose totally unappealing. The ultimate survivors have changed how they taste glucose, finding it bitter instead of sweet. Bye bye, traps.

How did this happen? It's not a learned behavior, something roaches pick up during their 1-2 year lives. Something changed in a specific group of German cockroaches in the early 1990s, when pest control workers started using glucose-laced poison traps to attract and kill roaches. Roaches apparently adapt to poisons regularly and resist their effects, forcing experts to develop new types of poisons. But this was something different.

Photo via photographer Erik Karits.

The roaches were avoiding bait they should find irresistibly sweet. A group of researchers at North Carolina State University took it upon themselves to figure out why and how this happened. Their resulting paper, published in Science, is titled "Changes in Taste Neurons Support the Emergence of an Adaptive Behavior in Cockroaches." The adaptation they discovered took place in the taste hairs on the roaches' bodies--their equivalents of the taste buds on our tongues.

"The three North Carolina researchers concentrated on [the taste hairs] around the mouth area and on two types of nerve cells that sense tastes and respond by firing electrical signals to the brain," writes the New York Times. "One responds only to sugars and other sweet substances; the other responds only to bitter substances. Whenever a molecule of something sweet attaches to a sweet detector, it fires electrical impulses and the roach brain senses sweetness, which makes it want to eat whatever it is tasting. Whenever a molecule of something bitter attaches to the bitter detector, that cell fires and the brain senses bitterness, which makes the roach want to avoid that substance."

Pretty straightforward--except, in some cockroaches, glucose fires off the bitter detector. The researchers don't know why, exactly, the mutation took place. Could generations of sugar averse cockroaches have survived and gradually made this a more common trait? Or did the bodies of these select German roaches evolve once bait traps started being used?

The researchers plan to study the mutation in more depth, and think their research could have broader ramifications, like figuring out how other insects--like mosquitoes--evolve. Understanding the molecular-level reasons for their behavior could help curb the spread of illnesses like the West Nile virus.

And, at the very least, it will help us keep cockroaches out of our kitchens, even when they shy away from our sweet sweet traps.