Oxitec reports that its insects behaved as planned — but a larger trial is needed to learn whether they can reduce wild mosquito populations.

Researchers have completed the first open-air study of genetically engineered mosquitoes in the United States. The results, according to the biotechnology firm running the experiment, are positive. But larger tests are still needed to determine whether the insects can achieve the ultimate goal of suppressing a wild population of potentially virus-carrying mosquitoes.

The experiment has been underway since April 2021 in the Florida Keys, a chain of tropical islands near the southern tip of Florida. Oxitec, which developed the insects, released nearly five million engineered Aedes aegypti mosquitoes over the course of seven months, and has now almost completed monitoring the release sites.

Based in Abingdon, UK, the firm reported the first results from the experiment during a webinar on 6 April, although it has not yet published the data.

Wild A. aegypti mosquitoes can carry viruses such as chikungunya, dengue, Zika and yellow fever, so scientists have sought ways to reduce their populations. Oxitec’s engineered males carry a gene that is lethal to female offspring. If all goes to plan, when