Bed bugs are evolving thicker exoskeletons to help them resist widely used insecticides.
Scientists at Australia's University of Sidney found the thicker a bed bug's cuticle, the more resistant it was to pyrethroid insecticides.
The team first took members of the Parramatta field strain of bed bugs, known to have high pyrethroid resistance, and exposed individuals to an insecticide.
Using scanning electron microscopy, they found that "mean cuticle thickness was positively correlated to time-to-knockdown, with significant differences observed between bugs knocked-down at 2 hours, 4 hours, and those still unaffected at 24 hours."
Insects with a cuticle thickness of around 10 micrometres were found to be effectively resistant to the pyrethroid, while those whose exoskeletons measured less than 9 micrometres succumbed in two hours or less.
In a second test, they exposed and examined members of the pyrethroid-susceptible Monheim laboratory strain of Cimex lectularius, and found they typically had cuticles of less than 9 micrometres, compared to the Parramatta bugs' ~10 micrometre exoskeletons.
The results suggest an explanation for why it's become increasingly hard to control bed bug infestation over time. Study co-author David Lilly says that this could have implications for future studies into methods of overcoming insecticide-resistant bed bugs, as well as other insects.
"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."