A new study from North Carolina State University shows the behavioral mechanism behind a sweet cockroach mating ritual that takes a bitter turn, resulting in rejected males.
Male German cockroaches (Blattella germanica) give females a “gift” of bodily secretions before mating that combines sugars and fats – think the cockroach version of chocolate – in order to attract and hold the attention of females long enough to begin copulation.
“This is a common mating behavior in insects and some other animals: males give females a tasty or valuable gift – it’s like Valentine’s Day, but every day,” Coby said. Schal, Blanton J. Whitmire Professor Emeritus of Entomology at NC State and co-corresponding author of the paper.
The study shows, however, that females opposed to simple sugar glucose get a nasty surprise when they mix their saliva with the male secretions – the saliva degrades the sweet treat of complex sugars into glucose, which becomes a bitter pill that ends the ritual. of courtship, the female fleeing without mating.
“We are seeing glucose-averse female German cockroaches refusing this nuptial gift — and the chance to mate — and we wanted to learn more about the mechanism behind it,” said NC lead researcher Ayako Wada-Katsumata. State and corresponding co-author of the article.
Generally, cockroaches like sugar. But some have developed an aversion to glucose; Wada-Katsumata published a paper in 2013 that showed the neural mechanism behind this aversion in German cockroaches, a behavior that may have become more pronounced due to the presence of simple sugar in roach baits placed inside. houses. In a 2021 paper, Wada-Katsumata and Schal showed that cockroach saliva converts complex sugars into glucose.
“The secretions of male cockroaches contain different types of sugars — in this case, maltose and maltotriose, which are generally preferred by females — as well as certain fats,” Wada-Katsumata said. Maltose is relatively easy to convert into glucose, while maltotriose is more complex and takes a bit longer to break down into glucose, she said.
“Cockroach saliva has a class of chemicals that break down sugars,” Schal said. “As the females feed on their present, the maltose is quickly converted into glucose, and the glucose-averse females experience a bitter taste and stop feeding, which also ends the mating opportunity.”
The mating process of cockroaches is interesting but probably unknown to bipeds. Males approach females, raise their wings, and release chemicals via the tergal gland on their backs. Females attracted to the secretion will climb onto the male’s back and feed on the secretion. While she is feeding, the male will telescope his abdomen under the female, grab her with an elongated, hooked penis, and move into position for mating. This courtship process only takes a few seconds; it is here that the rapid chemical conversion of complex sugars to simple sugars in saliva could kill the mood of glucose-averse women. If successful, however, the cockroaches engage in a back-to-back mating session lasting up to 90 minutes, with the male using a second penis to transfer a packet of sperm to the female.
In the study, the researchers performed various experiments to determine how glucose aversion affects courtship behavior in cockroaches. They found that glucose-averse females discontinued feeding more frequently due to their aversion, especially when feeding on a wild-type male – one who was not averse to glucose. Glucose-averse males often had higher levels of maltotriose in their secretions, which converted to glucose less readily and therefore gave these males more time to begin mating.
The researchers also modified the quality of male secretion, by substituting fructose for glucose and maltose secretions. Glucose-averse females relished fructose and fed on it longer, resulting in more successful mating sessions.
“This study is a direct way to show that secretion quality affects female behavior and mating success,” Schal said. “There is a trade-off between sexual selection and natural selection. Think of the deer as an example. Male deer have horns, not for natural selection – horns actually endanger males from predators and hunters – but for sexual selection to attract females and serve as useful weapons in competition with others. males. Similarly, the cockroach’s tergal gland evolved to attract females in the context of sexual selection.
“Wild-type females accept sweet secretions. Glucose-averse females do not accept wild-type secretions because they readily convert to glucose. Males may 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 causes the male to alter his sexual secretion and behavior,” Wada-Katsumata said.
The 2013 study advised bait manufacturers not to use glucose in baits. The 2021 studies extend this recommendation to all sugars that contain glucose. Baits made with glucose, sucrose, maltose and other sugars will be ignored by glucose averse cockroaches. As more cockroaches with an aversion to glucose survive, this trait will be passed on in greater numbers.
“We are constantly in an evolving battle with cockroaches,” Schal said. “Evolution can be enormously accelerated in the urban and human environment because the force of selection imposed on insects, especially indoors, is so intense.”
The study appears in Nature Communications Biology. Postdoctoral researcher Eduardo Hatano, Ph.D. student Samantha McPherson and Jules Silverman, Charles G. Wright Emeritus Professor of Entomology, co-authored the paper. The research was supported by the National Science Foundation under grant IOS-1557864, the US Department of Housing and Urban Development’s Healthy Homes Program (NCHHU0053-19), and the Blanton J. Whitmire Endowment at NC State.
– kulikowski –