For the first time, researchers have begun large-scale releases of the engineered insects, into a high-security laboratory in Terni, Italy.
"This will really be a breakthrough experiment," says Ruth Mueller, an entomologist who runs the lab. "It's a historic moment."
The goal is to see if the mosquitoes could eventually provide a powerful new weapon to help eradicate malaria in Africa, where most cases occur.
"It's very exciting," Mueller says.
NPR was the only news organization allowed into the lab to witness the moment the releases began in early February.
The lab was specially built to evaluate the modified insects in as close to a natural environment as possible without the risk of releasing them into the wild, about which there are deep concerns regarding unforeseen effects on the environment.