Humans have been locked in a struggle with disease-carrying mosquitoes for most of recorded history. With just two bites—one to pick up a pathogen and another to transmit it—the bugs have fueled countless outbreaks. Malaria exploded across Africa as humans first gathered for agricultural development. Yellow fever nearly wiped out Memphis, Tenn., in the 1870s as urbanization and river transport brought infected people and mosquitoes together. Some archaeologists suspect that mosquito-borne disease even hastened the fall of the Roman Empire.