In a 17-year study of cat fleas (Ctenocephalides felis felis), researchers tested egg samples—adult fleas being too difficult to collect and delicate to maintain—for signs of decreased susceptibility to the insecticide imidacloprid. The results showed no evidence of resistance to the insecticide among the tested cat flea populations, which came from 10 countries across the globe. (Photo credit: Michael K. Rust, Ph.D.)