Zika is spreading a little bit outside Brazil and Colombia, and a company called Oxitec is proposing a solution. In all likelihood they are twisting their data to fit their needs-to make it look like the mosquitoes they introduce really cause a decrease in the overall mosquito population.
News stories Here and Here for a sum-up of what they are proposing.
"Trials of the modified mosquitoes in Brazil, Panama and the Cayman Islands suggest they reduced local populations of Aedes aegypti mosquitoes by more than 90 per cent," Oxitec says.
Here's the problem from an evolutionary point of view-just because you have created this male Aedes aegypti mosquito which transmits the gene so that the offspring are killed before they reach adulthood doesn't mean that the females will mate with them. Even if the sexual selection be random, you will just eliminate the offspring of these males; but the other males, who are a large part of the population, will continue producing offspring. This is the best case scenario.
Sexual selection is not random-it is not like that females will mate with any mosquito-and if the mosquito population realize that the offspring of these genetically modified males are not reaching adulthood, they will probably weed them out by sexual selection even faster. Sexual selection by females will accelerate de demise of these traits.
From what Darwin explained in his Domestication of plants and animals and a little bit in the Origin of Species, it is clear that introducing new strains in a plant or animal is the easy part, the hard part is to make sure that their offspring survive the selection pressures of the others who are the more "stable" varieties. In his words, hybrids are easy to create-but will tend to revert to the stable varieties after a few generation, even if they can reproduce. Hybrids most likely will not even reproduce-and the reason was unclear to him-but the evidence is very strong that hybrids are difficult to breed, and even if they do breed, even more difficult is to ensure that their offspring survive and don't revert back to the parent varieties used to create the hybrid.
This thing about Zika males is very similar-and my bet is that introduction of these males has no effect whatsoever on the mosquito population of Zika.
Regarding the data from Brazil, Panama and Cayman Island-I think the data has been fudged to give them what they want to prove. And doing it in a lab setting may have nothing to do with how this turns out in real life-with loads of other selection pressures on the mosquitoes, both from within and outside their species. This is similar to the myth of antibiotic resistance in many ways.