By Richard Levine
Once again, a technique that modifies insects in order to control their populations has been proven effective. RIDL, which stands for Release of Insects carrying a Dominant Lethal, has been applied to diamondback moths, Mediterranean fruit flies, and olive flies, and it has been used in field trials on mosquitoes in order to reduce cases of dengue.
Scientists apply the RIDL technique to male insects in the lab, which basically makes them die young unless they receive a substance called tetracycline. As long as they have tetracycline, they will live, but take it away from them and they’re goners. It’s almost as if they’re breeding insects that are drug addicts from birth.
Next, they release millions of these male insects into the wild and allow them to mate with females. Since they no longer have tetracycline, the males die soon after mating. Their offspring, which also need tetracycline to live, will die before reaching adulthood since they have no access to the substance.
Using this technique, scientists have reduced the cases of dengue, which can be deadly, by 91% in a neighborhood called CECAP/Eldorado in the city Piracicaba, which is located in the Brazilian state of São Paulo. There were only 12 cases of dengue in the area, versus 133 cases the previous year. Surrounding areas also saw a reduction of dengue cases by 52%.
This is good news not only for potential victims of dengue, but also for people who may be susceptible to Zika, chikungunya, and yellow fever because the mosquito that transmits dengue — Aedes aegypti — also transmits these other diseases. The Brazilian health authorities and Oxitec, the company that produces the mosquitoes, call this undertaking the Friendly™ Aedes project.
“Over the course of one year, we were able to bring the dengue fever incidence down by more than 50% in Piracicaba — the outcome of diligent work to eliminate still water spots, the breeding site of the mosquito,” said the city’s Secretary of Health, Pedro Mello. “In CECAP/Eldorado, where we had the Friendly™ Aedes project, the reduction was extraordinary, going over 90%.”
“We are delighted with the result achieved so far by Friendly™ Aedes which shows the potential of our approach,” said Glen Slade, Oxitec do Brasil director. “We hope to see this effect on a larger scale beyond the limited area of CECAP/Eldorado with our expansion into Piracicaba’s downtown city.”
Friendly™ Aedes mosquitoes have been used in Piracicaba since April 30, 2015, when the first insects were released in CECAP/Eldorado. By January 2016, the technology had already reduced the number of wild Aedes aegypti larvae by 82% in the treated area, compared to a non-treated area.
This novel way of reducing the mosquito population has the added benefit of reducing the use of chemical insecticides. Scientists saw similar reductions of dengue in previous trials in the Cayman Islands in 2010 and in a suburb called Juazeiro, which is located in the state of Bahia in Brazil.
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Richard Levine is Communications Program Manager at the Entomological Society of America and editor of the Entomology Today Blog.