"We are the first group to collect lice samples from a large number of populations across the U.S.," said Dr. Kyong Yoon, a researcher at Southern Illinois University at Edwardsville, in a press release. "What we found was that 104 out of the 109 lice populations we tested had high levels of gene mutations, which have been linked to resistance to pyrethroids." Pyrethoids are a type of insecticide used for mosquitoes and other insects that contain permethrin, the active ingredient in over-the-counter lice treatment products. Yoon collected lice from 30 states, analyzing them for knock-down resistance, or kdr, mutations. Kdr...