by Emil Morhardt
The mosquito on the left is an Aedes aegypti female of the sub-Saharan African subspecies formosus. The one on the right is the cosmopolitan subspecies aegypti. Both species are vectors of yellow fever, dengue, and now Zika, but the African form historically breeds in tree holes and prefers non-human sources of blood; the cosmopolitan form evolved between 4000 and 6000 years ago, breeds primarily in human-generated containers, and prefers to feed on humans. Recently, the African form has taken up the breeding and feeding habits of the cosmopolitan one, though, and hybridization is apparently taking place. At the same time, the African form is moving into forested areas in South America, and the cosmopolitan form has gradually spread clear across the southern edge of the US, from Southern California to Florida, not doubt exacerbated by the warming trends.
The brief article in Science cited below points all this out, but offers little insight into just how worried those of us living in Southern California should be. As worried as if we lived in Miami? Evidently the hybridization has led to a wide range of probabilities of transmitting disease, and of susceptibility to insecticides. Evidently, just the appearance of the mosquito need not be a harbinger of a Zika epidemic, but the trends of mosquitoes increasing their range northward suggests that we may soon need more robust means of controlling them than exist at present.
Powell, J.R., 2016. Mosquitoes on the move. Science 354, 971-972.