Roach motels sit at the back of many a kitchen cupboard, bedroom closet, or bathroom cabinet. Yet, to the bane of human residents, only a few years after the traps were introduced in the 1980s, they lost their allure for an increasing number of German cockroaches. Researchers soon realized that some roaches had developed an aversion to glucose—the sugary bait disguising the poison—and that the insects were passing that trait on to their young. Now, scientists have figured out how this behavior evolved. Roaches, like other insects, detect taste through special 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, respectively. The researchers performed experiments on more than 1000 German cockroaches from the field and about 250 raised in the lab. The normal roaches happily lapped up both glucose and fructose, but the glucose-averse roaches ate only the fructose and spat out the glucose, the team reports online today in Science. Electrophysiological recordings indicated that glucose triggered sweet receptors in the normal roaches but bitter receptors in the other roaches. The change in behavior may save the insects' lives, but it does have its disadvantages: Glucose-averse roaches grow and reproduce more slowly than those with less finicky tastes.
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