Right. There are thousands of species of mosquito, most of which don't carry human diseases. Of the ones that do, many of are of African origin -- they evolved

Right. There are thousands of species of mosquito, most of which don't carry human diseases. Of the ones that do, many of are of African origin -- they evolved there along with us (and the diseases they carry). They are thus essentially invasive species in the rest of the world. The nice thing about potentially using CRISPR-based gene drives to extirpate (e.g.) Aedes aegypti is that it would affect only that species, unlike our current pesticides which tend to kill insects of many different species indiscriminately.