On a Tuesday morning in September, under a sweltering tropical sun on the island of Grand Cayman, 140,000 mosquitoes flit around in four large coolers in the back of a gray Toyota minivan. Behind the wheel is Renaud Lacroix, a Ph.D. in biology and medical entomology who works for the British biotechnology company Oxitec. A colleague, Isavella Evangelou, crouches behind him in a tight space next to the coolers. The minivan is idling on the side of a dirt road in West Bay, a quiet neighborhood where iguanas and roosters dart in and out of the yards of small homes painted in Caribbean pastels. The time has come for the mosquitoes to fulfill the purpose for which they were genetically engineered: a kamikaze mission to eliminate their own species.