Bed bugs – the blood-sucking bane of backpackers everywhere – are notoriously difficult to stamp out once they take hold. Not only can they survive a year without feeding, but they’re also rapidly developing resistance to insecticides.
Research led by David Lilly from the University of Sydney in Australia and published in PLoS One reveals a secret weapon harboured by super-resistant individuals – they literally have thicker skin than those that keel over within a couple of hours.
Most insect-controlling poisons are “contact pesticides” and are absorbed through a pest’s skin. In the case of bed bugs (Cimex lectularius) and other insects, it’s their exoskeleton or cuticle. And while genetic studies show insecticide-resistant bed bugs tend to overexpress genes that code for cuticle-building proteins, no one actually looked to see if this translated into a thicker cuticle.
Lilly and his colleagues took and bred bed bugs from a house in Parramatta, Sydney. When their blood-sucking subjects were nine days old, each was exposed to a common broad-spectrum insecticide, and the researchers measured the bugs’ “time-to-knockdown”.
After 10 minutes of insecticide exposure, they flipped each bug on its back. If it couldn’t get back on its feet, that point marked its “time-to-knockdown”. If it did, though, the test was repeated every 10 minutes until it stayed on its back, or until four hours were up.
Most died within a few hours. But some, incredibly, were still alive after 24 hours of insecticide exposure.
When Lilly sliced the legs these super-resistant bed bugs and compared them under a microscope to critters that succumbed within two hours, they found the resistant group’s cuticle was, on average, around 1.3 microns (or 15%) thicker than their susceptible counterparts’.
“If we understand the biological mechanisms bed bugs use to beat insecticides, we may be able to spot a chink in their armour that we can exploit with new strategies,” Lilly says.