Combined sewage overflow accelerates immature development and increases body size in the urban mosquito Culex quinquefasciatus

In urban landscapes the crowding of humans and their waste products may alleviate intra-specific interactions of common mosquitoes. Here, we present the results of a semi-natural experiment addressing the effects of water from a sewage overflow stream on density dependent fitness components and phenotypic traits of a common tropical and subtropical urban mosquito, Culex quinquefasciatus Say (Diptera: Culicidae). This semi-natural experiment was designed to quantify the relative importance of density dependence, weather forces and water quality on larval mortality, sex ratio and size at adult emergence. Results showed that mortality hazards were independent of larval density, decreased in sewage overflow water and increased with minimum temperatures. Under all rearing conditions adult mosquito size decreased with density. Mosquitoes from sewage overflow water emerged faster, were bigger and had an increased ratio of females to males. All these traits may contribute to the regulation of mosquito populations.