Forty-one percent of the world’s population lives where malaria is transmitted, according to the Centers for Disease Control and Prevention in Atlanta. One strategy that scientists are exploring for controlling the disease involves introducing transgenic mosquitoes resistant to malaria into natural mosquito populations. Although scientists have been researching many aspects of this strategy, it is not known whether the resistant mosquitoes would be able to replace the natural mosquitoes by producing more offspring, which is necessary for the technique to succeed. To find out, researchers from Johns Hopkins University in Baltimore studied mosquitoes that were modified to carry GFP and a gene that prevents infection by the malaria parasite. As seen in the images, the transgenic mosquitoes could be identified by the GFP-induced fluorescence in their eyes. After letting an equal mixture of transgenic and wild-type mosquitoes feed on malaria-infected mice, the researchers found that the percentage of transgenic mosquitoes increased from 50 percent to 70 percent after nine generations. The transgenic insects were not infected and, thus, more survived and laid more eggs. However, when given malaria-free blood, the transgenic mosquitoes were on equal footing with the wild-type mosquitoes and thus did not increase in percentage.The work is detailed in the March 27 PNAS and shows that the transgenic mosquitoes do have a selective advantage over wild-type mosquitoes when exposed to malaria. However, further research is needed to make the strategy applicable in the field, where only a small percentage of mosquitoes are exposed to malaria.