For generations, Eastern European Balkan region housewives have known that kidney bean leaves trap bedbugs, so they would spread an infested room at night with the leave and collect then burn them in the morning.
In 1943, a group of researchers studied this method and attributed it to microscopic plant hairs called trichomes that grow on the leaves’ surface and entangle the bed bug legs. Researchers wrote the findings in “The action of bean leaves against the bedbug,” but the Smithsonian reports World War II distracted the paper and they wound up receiving little attention for their work.
Now a group of American scientists from the University of California, Irvine, and the University of Kentucky are studying this bedbug-leaf interaction. “We were motivated to identify the essential features of the capture mechanics of bean leaves to guide the design and fabrication of biomimetic surfaces [or synthetic materials that mimic ones found in nature] for bed bug trapping,” they write in their paper.
The team of researchers put male bed bugs from a glass vial onto the bottom surface of kidney bean leaves, which captured the bugs within seconds. They used male bed bugs and not a mixture of both sexes to avoid making baby bed bugs.
A low-vacuum scanning electron microscope (LV-SEM) was used to allow the researchers to examine the bugs while they were trapped on the leaves. The images revealed that the trichosomes would hook the bugs’ feet like Velcro, but sometimes went right through. Of the bed bugs that were able to rip themselves free from the trichome by either breaking it or sacrificing their own leg. Usually if the bug did that, it would end up recaptured.
“It was astonishing to me that it worked at all,” says Catherine Loudon, a physical biologist at UC-Irvine and lead researcher of the new study, “You see this big muscular bug vigorously struggling, and it’s astonishing to me that the little tiny microscopic hairs don’t snap.”
Researchers are trying to create a synthetic material that mimics the surface of a bean leaf. “Keeping fresh bean leaves on hand isn’t an easy bed bug fix,” says Loudon: “The inconvenience of bean leaves is that not everyone wants them scattered around their bed room. Synthetics mimicking the surface of the bean leaf, however, could be placed as a ring around the bed legs, a floor mat at the door, a strip on the bed board, it could be something one put’s in one’s suitcase,” Loudon adds, since bed bugs “really only get from one place to another by walking or being carried.”
Scientists replicated the trichomes using polymers, but they ran into an issue. On the natural bean leaves, bugs were caught on average after six steps. With the synthetic surface, it took them on average, 39 steps to be just momentarily snagged, but they were never pierced, and were usually able to get through to move on.
Scientists didn’t let that get them down and they think they know what needs to be done. “Future development of surfaces for bedbug entrapment must incorporate mechanical characteristics of whole trichomes,” they concluded in their paper.
Dr. Loudon said, “It would be our greatest hope that ultimately this could develop into something that could help with this horrible problem.” She added, she and her colleagues have a patent on the technology pending. It has been optioned by a commercial company.
Bean Leaves Trap Bed Bugs
Bean leaves can trap bedbugs, UC Irvine researchers find: Next step is to perfect synthetic materials that can do the same. Video by Kate Loudon, UC Irvine ecology & evolutionary biology professor.