By human influence, cockroaches now avoid sweets

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When a male cockroach wants to mate with a female, he turns his rump to her, spreads his wings, and offers a home-cooked meal—sugars and fats squeezed out of his tergal gland. As the lovely lady nibbles, the male holds her with a penis while another penis delivers a packet of sperm.

If all goes well, a cockroach courtship can last around 90 minutes. But more and more cockroach intercourse is going strangely wrong, and contributing to more cockroach populations in places difficult to tame with conventional pesticides.

In 1993, scientists working at North Carolina State University (USA) discovered a feature in the German cockroach, a species that inhabits every continent except Antarctica.

Specifically, these new cockroaches didn’t seem to appreciate a form of sugar called glucose, which was odd because — as anyone who’s ever struggled with a cockroach infestation knows — cockroaches typically can’t get enough of sweets.

So where did these new, health-conscious cockroaches come from?

It seems we created them by accident, after decades of trying to kill their ancestors with sweet liquids mixed with poison. The candy-craving cockroaches ate the poison and died, while the less glucose-hungry cockroaches avoided death traps and survived long enough to reproduce, passing this trait on to the next generation.

“When we think of evolution, we usually think of wild animals, but it’s actually also happening to small animals that live in our kitchens,” said Ayako Wada-Katsumata, an entomologist at North Carolina State University.

Wada-Katsumata and her colleagues just added a tidbit to the cockroach story: according to a study published this month in the journal Communications Biology, the same trait that can help a female cockroach avoid sweet-tasting poisonous baits also makes her less likely to mate with normal male cockroaches.

This is because the cockroach’s saliva is able to quickly break down complex sugars, such as those found in the male’s mating proposal, and turn them into simple sugars, such as glucose. So when one of these glucose-averse females takes a bite out of the male’s nuptial gift, he literally bitters it in her mouth, and she runs away before he can complete the double sexual maneuver.

“Excellent!” you might be thinking. “The fewer cockroach connections, the less infestations we will have.” Take your time, the researchers said.

“How this is going to affect the population is really complicated,” Wada-Katsumata said.

That’s because, despite the problems, glucose-averse cockroaches still find ways to do the act.

In laboratory experiments, Wada-Katsumata and her colleagues showed that glucose-averse females are more skittish than wild-type cockroaches, which researchers call glucose-free cockroaches. However, they also found that glucose-averse males seem to compensate for this by making a more rapid transition to sex after offering their gift.

“Glucose-averse females can spend, say, three seconds feeding on the male’s secretions,” said Coby Schal, a professor of entomology at North Carolina State and author of the study. “The wild male doesn’t respond within three seconds. The glucose averse does.”

The researchers even have evidence to suggest that all these new pressures are causing changes in the chemistry of the glucose-averse male’s nuptial gift, possibly so that he continues to attract females.

From a scientific perspective, the German cockroach sugar saga shows how humans can drive both natural selection — the cockroaches that survive our poison traps — and sexual selection — the glucose-averse cockroaches that no longer want to mate with cockroaches. that even offer sweet snacks.

“I think that’s what makes this so interesting,” Schal said. “The idea that humans impose very strong selection on animals around us, especially indoors, and that animals respond not only with physiological changes but also with behavioral changes.”

The good news for consumers is that pesticide manufacturers share Wada-Katsumata and Schal’s enthusiasm for understanding cockroach evolution and are actively modifying their formulations to kill cockroaches to avoid glucose. Considering how new this research is, however, it will take some time for these changes to make their way to products on grocery store shelves.

“The worst thing you can have as a product is bait that is not eaten by cockroaches,” Schal said.

Translated by Luiz Roberto M. Gonçalves

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