There's a paper in PLOS One detailing an experiment with water butts where it was seen that mosquito breeding grounds in urban environments show higher populations, but lower species diversity. Interestingly, A. plumbeus (German wikipedia, as there is no English entry yet) seems increasingly to breed in this environment, which has a potential impact on public health as a carrier of West Nile virus.
“Mosquitoes in urban containers were less species-rich but present in significantly higher densities (100.4±21.3) per container than those in rural containers (77.7±15.1). Urban containers were dominated by Culex pipiens (a potential vector of West Nile Virus [WNV]) and appear to be increasingly exploited by Anopheles plumbeus (a human-biting potential WNV and malaria vector).”
The BBC have a news article on the story here.