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Daily News Blog

01
Jun

Cockroaches Show Increasing Resistance to Sugar-Laden Baits

(Beyond Pesticides, June 1, 2022) A new evolutionary strategy spreading among German cockroaches is making them more difficult to kill than ever before. In a recent publication in Nature Communications Biology, scientists determined that cockroaches are developing an aversion to sugar baits containing glucose, with impacts that are changing their behavior and altering their mating rituals. “We are constantly in an evolutionary battle with cockroaches,” said study co-author Coby Schal, PhD, of North Carolina State University. “Evolution can be sped up tremendously in the urban, human environment because the selection force imposed on insects, especially inside homes, is so intense.”

At issue with German cockroaches is a trade-off between natural and sexual selection. Natural selection or, in this case, human-induced natural selection, has led cockroach females to become averse to baits containing glucose sugars. While many are now familiar with the fact that the vast majority of German cockroaches are resistant to nearly every synthetic pesticide, with some resistant to upwards of 10x the label application rate, less reported is the pests’ growing resistance to sugar-laced baits. Sugar-containing baits have been employed for decades and, over time, cockroaches that are able to survive in locations where sugar baits were employed developed a distaste for the otherwise attractive solution.

As the present study shows, 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.”

While cockroaches having trouble mating sounds like a good thing, don’t get too excited. Glucose-aversion is likely to spread rapidly in populations where it exists. As far back as 2013, scientists made recommendations that manufacturers avoid using glucose in cockroach baits. With the current study, this recommendation is expanded to all sugars that contain glucose.

With synthetic pesticide use already precluded due to its lack of efficacy and high risk, the loss of effective baits to manage cockroach infestations has significant implications for pest management. It is particularly difficult because most manufacturers do not indicate whether their products do or do not contain glucose. However, there are still strategies that can be used to address cockroach infestations.

To manage cockroaches, focus on denying them access to the necessities of life –food, water, and shelter. Seal up cracks and crevices that may allow entryway, install door sweeps to further impede movement, and make sure food and water is never left out, and all surfaces are clean/vacuumed. Throughout the process, monitor populations with traps to gauge areas of activity, and the intensity of the infestation. Once you have done everything you can to deny food, water, and shelter, employ the only insecticide that cockroaches have not developed resistance to: boric acid.

Boric acid products can be formulated as a powder or bait. It may be worth an initial application of boric acid bait products in high infestation settings. In the context of the present study however, pay close attention to whether they are consuming the bait after it is applied. In any case, boric acid’s use as a desiccant can work to your advantage. Apply the product in powder form in very thin lines along areas where there is high cockroach activity. Cockroaches walking over the boric acid will have it attach to their feet or antennae. Then you can take advantage of cockroach grooming, a biological trait that has not (yet) been altered by human selection. Because cockroaches use their mouths to groom, pieces of boric acid they clean off of their bodies will be ingested, eventually resulting in death. Cockroaches also often feed on the carcasses of other dead cockroaches, potentially resulting in a positive feedback cycle that can help bring an end to an infestation. While we suggest the use of boric acid in bait formulations that do not off-gas, if handing powder formulations, use gloves and a mask

Once cockroach infestations are dealt with, don’t let up on sanitation or structural repairs. These pests are likely to return if conditions favor them. For a step-by-step checklist and guide to take care of a German cockroach problem, see Beyond Pesticides ManageSafe entry on this appalling pest.

All unattributed positions and opinions in this piece are those of Beyond Pesticides.

Source: NC State University press release, Nature Communications Biology

 

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