For decades, humans have set traps for cockroaches and laced them with sugar to attract the insects to their doom. But in response, some populations of cockroaches developed a self-preserving distaste for glucose, which allows them to steer clear of the traps.
As it turns out, though, a glucose aversion can kill the mood during cockroach mating, a ritual centered around a secreted sweet treat the male presents to the female.
In a study published last week in the journal Proceedings of the Royal Society B, scientists show that lab-raised German cockroaches have adapted to maintain their sex lives while still avoiding sugary baited traps. Males have tweaked the recipe for their sweet “nuptial gifts,” making their offerings more palatable to females that have been turned off to glucose by human-produced poisons.
The research “shows how this elaborate behavior [of a nuptial gift], which evolved presumably over hundreds of millions of years, has in just a short period of time been altered dramatically by humans,” Jessica Ware, an entomologist at the American Museum of Natural History who didn’t contribute to the findings, tells NPR’s Ari Daniel.
Despite their name, German cockroaches are found across the world, and they’re the most common species of cockroach in the United States. To initiate mating, the male raises its wings to reveal a sweet substance secreted from a gland on its back.
In terms of its chemical makeup, this nuptial gift is “similar to chocolate,” Ayako Wada-Katsumata, a co-author of the study and an entomologist at North Carolina State University, tells the Atlantic’s Katherine J. Wu. If she’s intrigued, the female climbs onto the back of the male to eat the treat.
While the female is feeding, the male initiates copulation. The two then have sex for about 90 minutes, which is how long it takes for the male to make a sperm package and pass it on to its mate, per NPR.
Humans have unintentionally messed with this process. Researchers created pesticides with glucose in an attempt to use cockroaches’ affinity for sugar against them. But in the 1980s in Florida, a population of German cockroaches seemed to develop an aversion to glucose and started avoiding the sweet poisons. Since then, researchers have discovered additional cockroach populations around the world that no longer like sugar, co-author Coby Schal, a North Carolina State University entomologist, tells the Atlantic.
But female cockroaches that lost their taste for glucose also lost their taste for males’ nuptial gifts. The males’ secretions include the compound maltose, which rapidly breaks down into glucose when mixed with females’ saliva. In a study published last year in Communications Biology, Wada-Katsumata and Schal found that when glucose-averse females tasted glucose from a potential partner’s gift, they stopped the mating ritual before it could begin, per Science’s Elizabeth Pennisi.
In the new study, the researchers show that glucose-averse male cockroaches have developed two traits to deal with this issue. First, they secreted more of a different compound called maltotriose, a more complex sugar that takes five minutes to break down into glucose in the female’s saliva. On the other hand, the maltose from the non-adapted male cockroaches converts to glucose in just a few seconds, per New Scientist’s Christa Lesté-Lasserre. Maltotriose is also “actually preferred by females,” Schal tells the New York Times’ Bethany Brookshire.
The glucose-averse males also initiate sex more quickly. While the other males took 3.3 to 3.9 seconds to start copulating, the glucose-avoidant males began within 2.2 seconds, before the females could sense the bad taste of the glucose. With these new tactics, the adapted males achieved improved mating results: They successfully mated in 60 percent of their attempts, compared to only about half the attempts for the others, Schal tells the Times.
“Overall, the male solution is to buy more time but speed up his copulatory attempt,” Schal tells NPR.
For their part, the females appear to be producing altered saliva—the new formula is not as good at changing maltose to glucose, allowing them to better tolerate the taste of their partner’s nuptial gift, the team reported in their study last year.
Given their mating success, the sugar-averse cockroaches could boost their reproduction rates and become more prevalent, per Science.
The findings highlight how resilient German cockroaches can be. The insects “overcome challenges over and over,” Chow-Yang Lee, an urban entomologist at the University of California, Riverside, who did not contribute to the study, tells the Atlantic. “You cannot help but have a lot of respect.”
Still, the study comes with a caveat: The new sex adaptations appeared in cockroaches raised in a lab, so “whether these are the traits that are really going to emerge in nature I think is open to discussion,” Richard ffrench-Constant, who studies the molecular biology of insects at the University of Exeter in England and did not participate in the research, tells the Times.