Here's the problem with sterilizing male mosquitoes using radiation: Females don't find them sexy anymore. Irradiating insects can be an effective control strategy, but it only works if the males remain buff enough to attract females--and irradiated male mosquitoes are sickly and unattractive. Oxitec, a four-year-old biotech company in Oxford, England, has come up with what could be a devastatingly clever solution: genetically engineered mosquitoes that are totally healthy, but have a "fertility switch" in their DNA. Males need a special food to be fertile. In the lab, fed the food, they mate and reproduce offspring that also have the genetic switch. But in the wild, without the food, the males immediately become sterile--able and willing to mate, but to no end. It's the perfect combination of virility and sterility: Released by the millions, the "repressibly sterile" males could crash a disease-carrying mosquito population, without the use of any pesticides. That could help control mosquito-transmitted plagues such as dengue fever and malaria. The technique might ultimately work on other kinds of insect pests as well. Malaysia, which has a serious dengue problem, is working with Oxitec to field-test the new bug.