Billions of sterilized male mosquitoes are needed to stop population growth
Screwworms, Medflies and tsetse flies have been successfully controlled in the past
Many questions remain about how well the radiation technique will work with mosquitoes
Editor’s Note: This is part two in a four-part series about efforts to stop or slow the spread of Zika virus though the use of modified and engineered mosquitoes. See all four pieces here.
The International Atomic Energy Agency recently announced a plan to help Brazil and other countries hard hit by the Zika virus produce “gamma-irradiated” sterile mosquitoes for mass release in those countries. Within the next few months, the agency says, it will send a cobalt-60 gamma cell irradiator to Brazil’s Moscamed research center in Juazeiro.
“The irradiator would allow our facility to produce up to 12 million sterilized male Aedes aegypti mosquitos per week,” said Moscamed Director Jair Virginio, “reaching up to 750,000 people in 15 municipalities … which have been particularly hard-hit by Zika.”
In the sterile insect technique process, or SIT, male insect pupae are subjected to sterilizing gamma rays. The insects are then raised in massive numbers and released in equally massive hordes to compete with wild males. It’s believed that if there are enough sterile males mating with females, the chances of producing offspring are reduced, and the population crashes.
Over the years, the technique has had some real success in reducing problem insects. Populations of moths, screwworms and fruit flies such as the Medfly have been brought under control in areas of the United States, while the tsetse fly has been tamed in Zanzibar using this method.
However, SIT requires a system of regular breeding, zapping and release of a mind-boggling number of insects to keep populations in check. For example, Guatemala’s El Pino facility produces more than 2 billion sterile Medflies each week for use in key areas of California and Guatemala.
Unfortunately, results with mosquitoes have been less successful. Radiation weakens mosquitoes more than it does fruit flies and screwworms. And the inbreeding that can occur while raising massive populations also takes a toll. So the gamma-irradiated male mosquito doesn’t seem to score with the girls as easily as his wild counterpart.
Scientists have played with reducing the gamma dose and are looking for alternative ways to sterilize the males. X-rays show some promise, as the dosage is less, plus using X-ray machines would reduce concerns about terrorists getting their hands on shipments of replacement radioisotopes as they cross international borders.
The IAEA admits the use of gamma irradiation in mosquitoes is still in pilot stages, with “encouraging results” coming out of Italy, Indonesia, Mauritius and China. The agency says it’s still working on how to separate males from females before the mosquitoes are zapped.
Next steps before this irradiated mosquito can become the answer to controlling Zika: Lots of research verifying survival, mating skill, and disease reduction.