An outbreak of dengue fever has parts of India mulling a controversial strategy: releasing hundreds of thousands of irradiated, sterilized male mosquitoes into urban areas, a technique that has shown itself to be highly effective but whose impact on the environment is mostly unknown.
The South Indian city of Chennai, where I am currently on assignment, is considering using the technique to boost an arsenal that has proven ineffective. The new strategy involves breeding tens of thousands of mosquitoes in glass houses, using a painstaking technique to separate the females from the males, and dosing the males with gamma rays that make them sterile. Male mosquitoes don’t sting. The hope is that the sterile males, once freed, will mate with females who will lay inert eggs.
A 2010 release in the Cayman Islands in the Caribbean caused the population of dengue-carrying mosquitoes to plummet by 80 percent. However, no one knows how the sudden elimination of part of the food chain affects other animals, or whether the absence of one species of mosquito might create an opening for something worse.
The state in which Chennai sits, Tamil Nadu, in September reported the highest number of dengue infections in the country: 5,000 cases of dengue fever, 39 of them fatal. The official numbers may mask a more profound problem, since international health experts believe that the states of India severely underreport the number of dengue cases. One dengue specialist has estimated that India sees 37 million cases of dengue fever a year.