In a recent study, SM1-transgenic Anopheles stephensi, which are resistant partially to Plasmodium berghei, had higher fitness than non-transgenic mosquitoes when they were maintained on Plasmodium-infected blood.  This result should be interpreted cautiously with respect to malaria control using transgenic mosquitoes because, despite the evolutionary advantage conferred by the transgene, a concomitant cost prevents it from invading the entire population.  Indeed, for the spread of a resistance transgene in a natural situation, the transgene's fitness cost and the efficacy of the gene drive will be more crucial than any evolutionary advantage.