Using Kidney Bean Leaves As A Roach Motel For Bedbugs

Image Caption: Bedbug on bean leaf (left); bedbug leg trapped by tiny, hair-like trichomes on leaf surface (right). Credit: M. Szyndler and C. Loudon / UC Irvine

Lawrence LeBlond for – Your Universe Online

Bedbug infestations have been on the rise in recent years, and a remedy of yore may just be the answer to controlling a large problem from such a little pest, especially since the critters are becoming increasingly resilient against pesticide control.

Researchers from the University of California, Irvine and the University of Kentucky (UKY) have rediscovered a type of plant that can be used as a bedbug trap, effectively stopping the insects in their tracks.

The kidney bean plant, or more appropriately the leaf of this plant, has microscopic hairs that can stab and trap the biting insects. The technique has been in use since at least the late 17th century, although the mechanisms of why the leaf worked were not known at the time.

According to Popsci, in 1678, English philosopher John Locke wrote that he would place kidney bean leaves under his pillow and around the bed to keep bedbugs from biting as he traveled through Europe.

Popsci’s Brooke Borel also noted that the method was common into the early 20th century throughout the Balkans. A report in 1927 from the Imperial and Royal Austro-Hungarian Army suggested that the leaves stunned bedbugs as they crossed over them in the night. In the morning, the bug-covered leaves would be removed and burned. Further evidence of the leaves’ use came in the 1940s when American entomologists noted that bedbugs, once attached to the leaves, “could hardly be induced to move.”

The new research from UC Irvine and UKY has taken a closer look at the leaves on a microscopic level, finding that minute hairs are responsible for grasping onto bedbugs, preventing an escape. With this knowledge in hand, the team is also researching ways to develop materials that mimic the pesticidal properties of the leaf. A paper on the research is published in today’s online issue of the Journal of the Royal Society Interface (RSIF).

With the dramatic rise in bedbug infestations in recent years, with invasions occurring in homes, schools, hotels and even hospitals, it has become an all-out war against the tiny pests. While they are not known to carry or transmit disease, their bite can be painful, causing burning, itching and/or swelling. It is important to catch and treat infestations early on, but the insects’ abilities to hide virtually anywhere, breed rapidly and catch human transport from place to place without detection, make fighting them difficult. And since they can thrive up to a year without a blood meal, they can remain hidden for long periods at a time, without detection.

Several pest control measures have been implemented in the face of the bedbug surge. Freezing, heating, vacuuming and commercial pesticides have been used in the fight against the insect, but none have been very reliable. And those who suffer the most often resort to ineffective and potentially hazardous measures, such as using non-approved insecticides rather than hiring a professional.

The notion that a leaf can be effectively used as a natural pesticide seems kind of far-fetched, said Catherine Loudon, a biologist at the UC 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 with the NY Times. “You can think of lots of reasons why it wouldn’t work. That’s why it’s so amazing.”

She said there is no indication that the kidney bean leaf and bedbug evolved to work together, but the leaf is very clever when it comes to exploiting the anatomy of the insect. The bug’s exoskeleton has thinner areas where its legs flex and its tiny claws protrude, allowing for the tiny leaf hooks to catch onto the bedbug’s “greaves.” And once a contact is made between the two, the rest is history.

“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.”

Loudon’s work was conducted along with collaboration from doctoral student Megan Szyndler and chemist Robert Corn, both of UC Irvine; and entomologists Kenneth Haynes and Michael Potter of UKY.

In the lab, the researchers discovered that, on average, bedbugs were snagged after taking just six steps across the leaf. Once the bugs were stuck, they tried to free themselves, but usually ended up becoming more stuck, flailing around their impaled limb(s).

Then, using the bean leaf as a template, the team micro-fabricated a material that closely mimicked the geometry of the leaf and put it to the test.

On the synthetic surface, the bedbugs were trapped, on average, after 39 steps. But unlike the natural leaf, the bugs were snagged only momentarily and their armor was never pierced, allowing them to free themselves easily and continue on. Loudon said this suggests that the crucial mechanics of the natural hooks, known as trichomes, still need to be worked out.

The bean leaves themselves could be useful pest control products, but they dry out fairly quickly and lose their grasping ability. They also cannot easily be applied to clothing, bedding and other fabrics. If the inner workings of the trichomes can be determined, a synthetic alternative can be produced to be applicable to specific surfaces.

“Plants exhibit extraordinary abilities to entrap insects,” said Loudon. “Modern scientific techniques let us fabricate materials at a microscopic level, with the potential to ‘not let the bedbugs bite’ without pesticides.”

“Nature is a hard act to follow, but the benefits could be enormous,” Potter added in a statement. “Imagine if every bed bug inadvertently brought into a dwelling was captured before it had a chance to bite and multiply.”

The team said they are not giving up on this just yet. “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.”

“It would be our greatest hope that ultimately this could develop into something that could help with this horrible problem,” Loudon told the Times, adding that she and her colleagues have a patent pending and one company has expressed interest in producing the material.

Source: Lawrence LeBlond for – Your Universe Online

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