To the human populations it coexists with, the Aedes aegypti mosquito continuously and ruthlessly spreads disease—most notably dengue fever and now Zika, too. After 100 years of using the same methods to battle these mosquitoes, the town of Piracicaba, Brazil, is finally turning to a new alternative. At a nearby facility run by Oxitec, biologists work to breed genetically altered Aedes mosquitoes, swatting away stray mosquitoes as they work. This new generation of mosquitoes has been modified to include a gene that prohibits their offspring from reaching adulthood. After being released from the Oxitec lab, these altered mosquitoes will mate, pass on their modified genes, and disable the next generation. Local mosquito populations will decline—and with them, the researchers hope, the spread of dengue and Zika.