An English biotech named Oxitec, has tried to conduct a scientific experiment to reduce the number of native disease-carrying mosquitoes. They did so by releasing millions of genetically modified mosquitoes into neighborhoods in Jacobina, Brazil, from 2013 to 2015. However, the experiment has received severe backlash after it was found that some of the gene-edited mosquitoes passed on their genes to the native insects. This has, in turn, fueled concerns that they created a more robust hybrid species.

The company Oxitec experimented by releasing nonbiting-male Aedes aegypti mosquitoes, which bore a gene that should doom most of their offspring before adulthood. For this, they released around 450,000 genetically modified male Aedes aegypti each week for 27 months. It is to be noted that Aedes aegypti spread a number of diseases, including Zika virus, dengue fever, yellow fever and West Nile virus.

These GM mosquitoes were supposed to flit along and mate with females (the sex that bites humans) and then die, passing their lethal genes to similarly doomed offspring. However, it was found that about 3% of the females, which mated with the genetically modified males, would produce offspring. What surprised more was that of the small number of offspring that survived, most were weak and unable to produce offspring of their own.

But, a group of researchers are raising questions on whether this method went as planned by Oxitec. The researchers found that some of the genes from the genetically modified mosquitoes had transferred to the native population, resulting in a new hybrid of Brazilian mosquitoes and the genetically modified mosquitoes. The study was published in the journal Scientific Reports on September 10.

Senior author Jeffrey Powell, a professor of ecology and evolutionary biology at Yale University, said in a statement, “The claim was that genes from the release strain would not get into the general population because offspring would die. That obviously was not what happened. However, there is no known health risk to humans that might come from these hybrids. But it is the unanticipated outcome that is concerning.”

The researchers noted that this mixing of genes might have led to a ‘more robust population,’ making it better able to resist insecticides or transmit diseases, as reported.