Suburbanites may be blissfully unaware, but for city dwellers it’s one of nature’s ultimate truths: cockroaches love sweets. Sure, the repulsive, disease-carrying insects eat anything at all, from moldy cat food to the stinkiest cheese — but given a choice, they’ll always go for the sugar.
Or rather, they used to. According to a new study in Science, some roaches’ tastes are evolving to the point where they’re refusing to gobble down glucose, a form of sugar commonly found in plants. “They now perceive glucose as bitter,” says Coby Schal, an entomologist at North Carolina State University and one of the report’s authors. And while that might sound like good news for the roach-infested, it’s not: sucrose is the key attractant used in roach traps — and many of the nasty little creatures are no longer interested.
How did this happen? Turns out it may be our fault.
When prehistoric roaches lived in the wild, experts have theorized, it made sense to be glucose-averse — that mutation helped them avoid glucosides, or toxic glucose-containing molecules found in certain plants. “They’re nasty substances,” says Schal.
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But when cockroaches joined us in caves, and ultimately in homes — away from the threat of glucosides — “they would have lost this trait, because it became maladaptive,” says Schal. Regular sugar, after all, is a highly concentrated source of energy, and if roaches were wired to avoid it, their odds of survival would drop. “If you brought them a Krispy Kreme donut,” Schal explains, “they couldn’t eat it.”
The mutation remained in the genome, though. And when humans began putting glucose in roach poison, we reactivated it — so much so that when some roaches now taste sugar, Schal says, “they jump back as though you’ve given them an electric shock.”
So goes the theory, anyway. A true test will have to wait until molecular biologists decode the cockroach genome and look at the changes that might have taken place in roach DNA over recent decades. “We have roaches in the freezer that date back to the 1930s,” says Schal. “This is what’s going to be driving our research over the next five or 10 years.”
But all hope of trapping these mutant critters is not lost. Sucrose-averse roaches are still attracted to fructose, or fruit sugar, and maltose, which is found in beer (“They really love that stuff,” says Schal). So the proprietors of the Roach Motel need only switch flavors to stay in business.