In January, entomologists will start deploying a strange bacterium called Wolbachia pipientis in an attempt to halt disease transmission by mosquitoes. Their target is Aedes aegypti, the mosquito that transmits dengue, a human viral disease that causes crippling joint and muscle pains. Recent studies have shown that infection with Wolbachia makes mosquitoes resistant to the dengue virus. Now, a team at the University of Queensland in Brisbane, Australia, wants to test whether they can spread Wolbachia in the wild by setting free small numbers of mosquitoes infected with the microbe.