Journal of the Royal Society

Leaves. Leaves!

In the battle against bedbugs, we humans have tried everything from glue sheets to industrial-grade poisons to heating our houses to 140 degrees. And yet we are losing.

A potentially vastly more simple treatment turns out to also be cheaper and natural: cover the infested area in bean leaves. Just six "steps" (36 footfalls) after walking onto a bean leaf, the average bedbug is trapped. After 19 ambulatory cycles, 90 percent of bedbugs had been snagged.

These revelations on bug locomotion are the fruit of a new study, published this week in the Journal of the Royal Society, examining the highly effective "bean leaf" infestation remedy, a traditional Balkan method for dealing with the pests. How did we not know about this before? "The distraction of the Second World War," the paper notes, "undoubtedly prevented the 1943 report ‘The action of bean leaves against the bedbug’ from gaining as much attention as it would have otherwise."

A couple years ago, when Michael Potter, an urban entomologist at the University of Kentucky, was writing "The History of Bedbug Management -- With Lessons from the Past," he came across this unusual solution. So he and colleagues from Kentucky and UC-Irvine set out to figure out just what made bean leaves so good at trapping bedbugs.

The answer, they found, lies in microscopic leaf hairs called trichomes. Bean leaf trichomes have hooks that pierce the legs of the bugs as they attempt to cross, making this humble leaf the world's most effective known trap for bedbugs.

Next question: could a synthetic material reproduce that effect? Using high-tech molding, the researchers created replica leaves with replica trichome hooks. Unfortunately, they weren't as effective as the real thing.

"The synthetic ones have the exact same morphology," says Kenneth Haynes, a professor of insect behavior at the University of Kentucky and one of the co-authors. "They're just as sharp, just as curved, they have the same diameter -- so there's some other characteristic of that hook that we need to work towards perfecting."

Bedbug infestations have surged over the last decade, and among the hypotheses for that phenomenon is the fact that bedbug populations have developed resistance to some insecticides. This makes a physical solution, like traps, all the more desirable.

LV-SEM images of bed bug legs (yellow) on bean leaf surfaces with hooked trichomes (green). (a) Piercing under a pretarsal claw leads to entrapment of a bug by a leaf. (b) Piercing occasionally occurs at a tarsal intersegmental membrane, also causing entrapment of a bug. (c) Higher magnification of piercing from (a). (d) In contrast, hooking causes momentary snagging of a bug leg.

There's still work to be done before a store-bought "leaf" can act as an early warning system for homeowners. Even if the "leaf" develops near-perfect trapping ability, what does an amateur exterminator do next? The traditional method is to burn the buggy leaves, though ideally, a synthetic trap would be reusable. "A strong vacuum could get them off," Haynes says. "The question would be: can you clean the surface well enough without damaging the surface?"

While we wait for science to catch up to nature, get your hands on some bean leaves and see if you have any bed bugs crawling around.

All images courtesy of the Journal of the Royal Society.

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