Scientists to turn to plants for bed bug control

Bed bugs, beware — the scourge of homes, hotels and hospitals may someday be defeated, thanks to a group of U.S. university scientists and a palmful of leaves.

Researchers in California and Kentucky recently uncovered the bed-bug-slaying secrets of the kidney bean plant; now, in the spirit of biomimicry, they’re attempting to replicate the plant’s defensive weaponry.

There’s a reason we’re admonished to “not let the bed bugs bite.” These stealthy insects thrive in human habitats, where the four-millimeter creatures emerge at night to dine on our blood. They leave behind itchy rashes, blood-smeared feces and heebie-jeebies.

Bed bugs are notoriously tough to kill. They can survive for days at below-freezing temperatures and withstand the evaporation of a third of their weight in water. Adults can pass an entire year without feeding. Many have developed resistance to common pesticides, much to their exterminators’ chagrin.

This increased resistance, combined with a highly mobile human population, has allowed bed bug numbers to skyrocket. Across the United States, calls to bed bug exterminators increased 57 percent between 2005 and 2010. With many pesticides rendered unreliable, exterminators must vacuum, freeze or bake entire buildings to make sure all the bugs are killed.

But these methods are costly, imprecise and inconvenient. Now, scientists are seeking help from the creatures that have been quietly building anti-insect arsenals for millions of years: plants.

For centuries, people in Serbia, Bulgaria and other parts of southeast Europe have relied on leaves from kidney bean plants as quick and easy bed bug control. Residents toss a handful of kidney bean leaves around their beds at night, and bugs wandering across the leaves are permanently snared within a few steps. Remove and burn the leaves, and the bugs are gone for good.

Recently, researchers at the University of California Irvine and the University of Kentucky teamed up to figure out just how these kidney bean leaves work. They published a paper this month in the Journal of the Royal Society Interface, a journal dedicated to showcasing projects that link different aspects of the physical and life science fields.

The researchers included a doctoral student, three entomologists and a chemist. Using electron microscopy, the team surveyed the surface of a kidney bean leaf and discovered its secret: a field of trichomes, or microscopic hooked hairs. Imagine walking across a room where the floor is studded with inch-thick meat hooks that arch ankle-high, sharp points curving downward to aim at your bare feet. Then imagine that you have six feet, all slipping, sliding and snagging.

This, according to electron microscope images, is what bed bugs face when they stroll across a kidney bean leaf. Sometimes, an insect’s foot slides unharmed from underneath a trichome’s arch. Usually, though, a hook stabs through the bug’s armored cuticle within seconds of stepping onto the leaf. The bed bug can escape only by breaking the sturdy trichome or by ripping through its own foot.

Once they’d discovered the trapping mechanism, the team attempted to replicate natural trichomes with synthetic substances. They used a leaf to make a negative mold that contained a precise impression of each trichome. They then filled in the impressions with a positive mold, producing a synthetic surface studded with replicated trichomes, just as sharp and sturdy as the originals. A variety of substances were used for the lab-made trichomes, each chosen to mimic a range of mechanical properties inherent to the cell walls of natural trichomes. Sometimes, natural trichome tips were left embedded in the original mold, thus becoming glued to the tips of the now hybrid natural-synthetic structures.

Trichomes fabricated, the team tested the bug-snagging powers of their synthetic creations. Unfortunately, the synthetic materials proved no substitute for nature’s weaponry — not yet, at least. So far, the synthetic surfaces made the bed bugs stumble, but not stop. The bugs tended to slip their feet into and out of the trichomes’ arches without becoming permanently snagged. Even when wandering across the hybrid surfaces, encountering synthetic trichomes tipped in natural material, the bugs evaded capture.

The researchers double-checked their trichomes’ sharpness and durability; all was well. They began to suspect that natural trichome stalks are partially or completely hollow, allowing the trichomes more flexibility to drag along insects’ legs before catching and piercing the cuticle.

Despite this initial setback, the researchers are still hopeful that their materials and techniques can be honed to yield a successful product. There’s plenty of motivation driving this project forward—pesticide-free bed bug snaggers could do wonders for extermination efforts. Bed bug-proof floor mats, for example, could be shifted and reused; bug-snagging panels could be attached to door thresholds and bed frames.

Michael Potter is an entomologist at the University of Kentucky and a collaborator on the bed bug project.

“Nature is a hard act to follow,” he told University of California reporters, “but the benefits could be enormous. Imagine if every bedbug inadvertently brought into a dwelling was captured before it had a chance to bite and multiply.”

“Plants exhibit extraordinary abilities to trap insects,” commented Catherine Loudon, entomologist at the University of California Irvine and the paper’s lead author. “Modern scientific techniques let us fabricate materials at a microscopic level, with the potential to ‘not let the bedbugs bite’ without pesticides.”