Have you ever wished you could just turn off your sweet tooth to help you resist that third piece of pie? For people, the downside of the deliciousness of sugar is simply feeling really full or gaining weight, but for cockroaches, their sweet tooth can be deadly.

The poisoned baits people set to kill roaches in their homes lure the unsuspecting insects in with sugar. But it turns out that the selective pressure of delicious, deadly traps throughout the environment has led to the rapid evolution of cockroaches that avoid sugar. They turned the sweet tooth off—or rather redirected it so it now tastes bitter.

A team of researchers from North Carolina State University published research this week looking at how the German cockroach, Blattella germanica, was able to adapt so quickly when surrounded by tasty insecticide. Sweet baits became popular for roach control in the mid-1980s, but several years later scientists began noticing a new behavioral trait: aversion to glucose, the most common simple sugar. The trait is heritable, and cockroaches with it avoided the baits. In areas treated with these traps, the roaches without a sweet tooth had much better survival rates than the roaches that lacked this new adaptation.

Insects’ sense of taste comes from hair-like structures on the mouthparts that contain nerve cells called peripheral gustatory sensory neurons. Insects have four “tastes”—sweet, bitter, water, and salt. Typically, foods that trigger the sweet neurons led the insects to eat, while foods that trigger the bitter neurons cause them to avoid that food.

The scientists, Ayako Wada-Katsumata, Jules Silverman, and Coby Schal, suspected that a change in the bitter and sweet sensory systems led to the glucose aversion trait. When they compared the sugar and bitter sensitivities of the averse roaches with the wild type, they found that the glucose triggered the same neurons as caffeine — very bitter. However, both groups of roaches still ate fructose, another simple sugar molecule, at the same rates.

Sampling wild cockroaches, they found glucose-averse individuals in seven out of 19 populations. The sensory responses in the native cockroaches mimicked the lab experiments, with caffeine and fructose responses remaining normal and glucose triggering the bitter system instead of the sweet. This shows that a very similar glucose aversion mechanism arose in multiple populations.

What kind of mutation led to this adaptive behavior? The researchers suspect that one or more mutations modified the bitter sensing system to react to glucose. For populations surrounded by sweet poisons, this mutation offers a serious evolutionary advantage. However, growth and reproduction of the glucose-averse roaches is slower than the normal population, so the mutation only functions as an adaptation in the face of attempted pest control.

The more we try to poison the roaches, the greater the advantages of being a cockroach that thinks sugar tastes bitter, and the more common this mutation will become. We probably need to find a new type of insecticide.

Science, May 2013. DOI: 10.1126/science.1234854 (About DOIs)