Bean Leaves Are Natural Bedbug Traps

 Images of bed bug legs (yellow) on bean leaf surfaces with hooked trichomes (green). Scanning electron microscope photo from The Royal Society

Smithsonian:

Recognizing this ongoing problem, researchers are constantly trying to come up with new methods for quickly and efficiently killing the pests. The latest technique, described today in the Journal of the Royal Society Interface, takes a hint from mother nature and history. For years, people in Eastern Europe’s Balkan region have known that kidney bean leaves trap bedbugs, sort of like a natural fly paper. In the past, those suffering from infestations would scatter the leaves on the floor surrounding their bed, then collect the bedbug-laden greenery in the morning and destroy it. In 1943, a group of researchers studied this phenomenon and attributed it to microscopic plant hairs called trichomes that grow on the leaves’ surface to entangling bed bug legs. They wrote up their findings in “The action of bean leaves against the bedbug,” but World War II distracted from the paper and they wound up receiving little attention for their work.
Rediscovering this forgotten research gem, scientists from the University of California, Irvine, and the University of Kentucky set out to more precisely document how the beans create this natural bedbug trap and, potentially, how it could be used to improve bedbug purging efforts. “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.
They used a scanning electron microscope and video to visualize how the trichomes on the leaves stop the bedbugs in their ravenous tracks. Rather than a Velcro-like entanglement as the 1943 authors had suggested, it seems that the leaves stick into the insects’ feet like giant thorns, physically impaling the pests. Knowing this, the researchers wondered if they could improve upon the method as a way to treat bedbug infestations, because leaves themselves dry out and can’t be scaled up to larger sizes. “This physical entrapment is a source of inspiration in the development of new and sustainable [or scalable and chemical-free] methods to control the burgeoning numbers of bed bugs,” they write. They used fresh bean leaves as a template for micro-fabricating produced surfaces that precisely mimicked the leaves. To do this, they created a negative molding of the leaves, then poured in polymers sharing a similar material composition of the living plant’s cell walls. The team then allowed bedbugs to walk across their synthetic leaves to test their effectiveness compared to the real deal. The fabricated leaves did snag the bugs, but they didn’t hinder the insects’ movements quite as effectively as the living plants.

Another example of learning from nature.