(PhysOrg.com) -- Bed bugs, once nearly eradicated in the built environment, have made a big comeback recently, especially in urban centers such as New York City. In the first study to explain the failure to control certain bed bug populations, toxicologists at the University of Massachusetts Amherst and Korea’s Seoul National University show that some of these nocturnal blood suckers have developed resistance to pyrethroid insecticides, in particular deltamethrin, that attack their nervous systems.