The third phase field study of Singapore's stealth weapon against dengue has been a success, achieving 90 per cent suppression of the urban mosquito population at test sites, paving the way for an expanded fourth phase study next month. This will involve the release of mosquitoes via drones, said the National Environment Agency. The program uses the release of male mosquitoes carrying the Wolbachia bacterium mate with females, causing them to lay eggs that do not hatch.