But the main reason why it’s boom time for bedbugs, according to the review, is that they’ve evolved resistance to many pesticides, our main line of defense. Indeed, these critters are now resistant to “most of the major classes of insecticides,” the review states, including pyrethroids, which is still one of the most commonly used insecticides. They’ve also developed resistance to DDT, which attacks insects in a similar way to pyrethroids.