British biotech company Oxitec conducted a 27-month long experiment in 2013 Jacobina, Brazil, aimed at reducing the local mosquito population by 90 percent while preserving the genetic integrity of the local insect population.
The overall goal was to curb the spread of mosquito-borne diseases, such as yellow fever, dengue, chikungunya, and Zika, by releasing half a million OX513A mosquitoes. The insects are a genetically-modified version of the Aedes aegypti mosquito, which combined a breed from Mexico with a breed from Cuba.
The mosquitoes were supposed to contain a dominant lethal gene that would render the first generation of future offspring infertile (while also marking them with a fluorescent green protein gene). Well, as it often does, life found a way.