Just after sunrise in early January, a delivery van trundled along a suburban street in Queensland, Australia. Inside were tubs filled with a type of mosquito that carries dengue fever, the flulike illness that annually sickens 50 million to 100 million people worldwide. Workers inside the van stopped at every fourth house, took out what resembled a small Chinese food container and released 40 mosquitoes into the wild. After a week, they had filled the air with 6,000 insects. By early March they had launched 72,000.