The idea made sense on paper: Introduce male mosquitoes genetically engineered to be sterile into the bug population and watch the insect numbers drop. As New Atlas reports, that's generally what happened in a Brazil experiment—but only for about 18 months. At that point, the numbers rebounded, say Yale researchers in a new study at Scientific Reports. But perhaps more troubling is this: Scientists say the modified genes are now showing up in the mosquito population, which was not supposed to happen. This is "very likely resulting in a more robust population than the pre-release population due to hybrid vigor," the researchers write in the study. The British company behind the experiment, Oxitec, strongly disputes the findings and tells Gizmodo it is trying to have the study retracted or corrected.
The Yale researchers, though, say the results are clear. "The claim was that genes from the release strain would not get into the general population because offspring would die,'" says senior author Jeffrey Powell in a news release. "That obviously was not what happened." Before the test, the estimate was that 3% to 4% of the ostensibly sterile mosquitoes would manage to produce offspring, but those offspring were expected to be too weak to survive. Those predictions now appear to have been too optimistic. Researchers are not saying that the new strain of mosquitoes necessarily poses a greater health risk to people in Jacobina, where the study took place. But "it is the unanticipated outcome that is concerning," Powell tells New Atlas. (Maybe mosquito diet pills will work better?)