Hooks on the bean leaf exploit thinner areas in the bedbug’s exoskeleton to trap it, scientists have discovered. The more the bug struggles to raise its legs to free itself, the more stuck it gets.
Generations of Eastern European housewives doing battle against bedbugs spread bean leaves around the floor of an infested room at night. In the morning, the leaves would be covered with bedbugs that had somehow been trapped there. The leaves, and the pests, were collected and burned — by the pound, in extreme infestations.
Now a group of American scientists is studying this bedbug-leaf interaction, with an eye to replicating nature’s Roach Motel.
A study to be published Wednesday in The Journal of the Royal Society Interface details the scientists’ quest, including their discovery of how the bugs get hooked on the leaves, how the scientists have tried to recreate these hooks synthetically and how their artificial hooks have proved to be less successful than the biological ones.
At first glance, the whole notion seems far-fetched, said Catherine Loudon, a biologist at the University of California, Irvine, who specializes in bedbug locomotion.
“If someone had suggested to me that impaling insects with little tiny hooks would be a valid form of pest control, I wouldn’t have given it credence,” she said in an interview. “You can think of lots of reasons why it wouldn’t work. That’s why it’s so amazing.”
But even though there is no indication that the bean leaves and the bedbugs evolved to work together, the leaves are fiendishly clever in exploiting the insects’ anatomy. Like the armor covering knights in medieval times, the bedbug’s exoskeleton has thinner areas where its legs flex and its tiny claws protrude — like the spot where a greave, or piece of leg armor, ends.
“The areas where they appear to be pierceable,” Dr. Loudon said, “are not the legs themselves. It’s where they bend, where it’s thin. That’s where they get pierced.”
This folk remedy from the Balkans was never entirely forgotten. A German entomologist wrote about it in 1927, a scientist at the United States Department of Agriculture mentioned it in a paper in 1943, and it can be found in Web searches about bedbugs and bean plants.
But the commercial availability of pesticides like DDT in the 1940s temporarily halted the legions of biting bugs. As their pesticide-resistant descendants began to multiply from Manhattan to Moscow, though, changing everything from leases to liability laws, the hunt for a solution was on.
The first task was to determine exactly how the hooks — the technical name is trichomes — worked. The process was viewed through an electron microscope, Dr. Loudon said. “The foot comes down onto the surface, but as it’s lifting up, it’s catching on these hooks,” she said. “The point is pointing down. So all of their legs get impaled.”
“And as soon as one leg gets caught,” she added, “they are rapidly moving legs around and try to get away on the surface. That’s when they get multiply impaled.”
Dr. Loudon and her co-authors — Megan W. Szyndler and Robert M. Corn from Irvine and Kenneth F. Haynes and Michael F. Potter of the University of Kentucky — then set out to mimic the mechanism.
Using a casting process similar to one a sculptor might choose, the scientists replicated, with polymers from different epoxies, the geometry of the trichomes, the sharp point on their tips and their flexibility and strength. Sometimes the tips of the hooks broke off during the molding process, resulting in a hybrid of biological and fabricated materials.
On the natural leaves, bugs were snagged, on average, after six steps, or locomotory cycles. (In one cycle, each of the insect’s six legs moves once.) Once stuck, they tried to free themselves, but they usually ended up just flailing in place around the impaled limb.
The bugs, however, were largely unimpeded by the synthetic surfaces. According to the study, it took them, on average, a Hitchcockian 39 steps to be momentarily snagged, but their armor was never pierced, and they usually moved on.
The scientists, though, 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.
And they are far from giving up. As they wrote in the study, “With bedbug populations skyrocketing throughout the world and resistance to pesticides widespread, bio-inspired microfabrication techniques have the potential to harness the bedbug-entrapping power of natural leaf surfaces.”
Or as Dr. Loudon said, “It would be our greatest hope that ultimately this could develop into something that could help with this horrible problem.” Already, she said, she and her colleagues have a patent on the technology pending. It has, she said, been optioned by a commercial company.