Cockroaches are Evolving to Prefer Low-Sugar Diets

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Pamela Appea in Salon: Apparently, humans aren’t the only animals going keto. The German cockroach (Blattella germanica), one of the most common pests in the world, is evolving to have a glucose-free diet. Unlike many humans, it’s not because they’re suddenly watching their figure; rather, German cockroaches have inadvertently outwitted human pest control tactics by evolving to dislike sugar, specifically glucose.  That could have huge implications for the population of cockroaches worldwide, which is of particular concern given their propensity to spread bacteria and disease.

The not-so-sweet insight emerged from new research coming out of North Carolina State University, where scientists study roach reproductive habits and evolutionary adaptations. There, Dr. Ayako Wada-Katsumata and a team of entomology researchers found evidence of significant changes involving sugar-averse German cockroaches and mating habits.

According to Dr. Coby Schal, professor of Urban Entomology, Insect Behavior, Chemical Ecology, Insect Physiology and head of the eponymous Schal Lab at North Carolina State University, the team’s new research shows that cockroaches have begun to deviate significantly compared to previously observed roach-mating behavior. Female lab roaches, housed in North Carolina lab originating from a Florida-strain, included a significant population of glucose-averse roaches; glucose is a simple sugar that is intrinsic to the processes of plant and animal life.

According to Beyond Pesticides: The implications of this development are affecting a critical life stage of the German cockroach: mating. Roach copulation is initiated by males approaching a female and exposing a specialized gland on its abdominal segment, which subsequently excretes a sugary concoction that is intended to attract the female. Females feeding on the gland are thus at the right position for males to mate. Copulation is generally more successful when females feed for longer periods of time; a successful courtship can last up to 90 minutes.

It follows that bait aversion has come to an evolutionary reckoning with cockroach mating rituals. For female cockroaches, something tastes a bit off. “We’re seeing glucose-averse female German cockroaches turning down this nuptial gift – and the chance to mate – and wanted to understand more about the mechanism behind it,” said Ayako Wada-Katsumata, PhD, study coauthor and research scholar at NC State. Male excretions contain a range of sugars and amino acids that females rapidly break down into glucose with their saliva. But with natural selection dictating a need to avoid these sugars, female cockroaches averse to glucose taste bitterness when feeding on the solution, resulting in a short and failed courtship.

According to the study, glucose-averse females mated at a significantly lower rate with wild type male cockroaches (lab-reared cockroaches without sugar aversion). There was no significant difference seen when glucose-averse males mated with glucose averse females. However, even within glucose-averse pairs, their courtship was much shorter than wild type mating events. Looking closer at the nuptial secretions, scientists found that by adding fructose to the secretion of wild type males, they could increase their mating success with glucose-averse females.

“Wild-type females accept the sugary secretions,” said Dr. Wada-Katsumata. “Glucose-averse females don’t accept the wild-type secretions because they easily convert to glucose. Males can change the composition of secretions – perhaps producing more maltotriose which takes longer to convert to glucose – or try to mate faster. In short, the glucose aversion trait evolved under natural selection, but under sexual selection it is causing the male to modify his sexual secretion and behavior.”