The sex structure of the larval populations of the urban mosquito <Emphasis Type="Italic">Culex pipiens pipiens</Emphasis> f. <Emphasis Type="Italic">molestus</Emphasis> Forskal (Diptera,Culicidae) in St. Petersburg

The study of sex ratio in larval populations in the urban mosquito Culex pipiens pipiens f. molestus inhabiting underground sites in St. Petersburg was carried out for the first time in 1997–2001, as part of monitoring of local populations of this mosquito in order to estimate its reproductive potential. Samples of the immature stages were regularly collected in the underground breeding places flooded with water with a varying degree of pollution in five city districts (altogether 27 samples, 14 251 larvae). Pupation was observed under laboratory conditions at 20°C for 6–46 days. The sex was determined at the pupal stage. In 19 samples collected in basements of dwelling houses the incidence of males widely varied from 40.2 to 65.6%, and the sex ratio (males: females), from 0.7: 1 to 1.9: 1. Medians defining the percentage of males in the populations in different basements during a certain period (from 3 to 11 months) were 57.5%, 47.0%, and 50.2%. The greatest incidence of males (the median being 62.2%) and sex ratio from 1.1: 1 to 3: 1 was observed in autumn in 1999–2001 in populations inhabiting the sewer pipe. Analysis of all the 27 samples showed that the males constituted on the average 54.5%, i.e., that is the sex ratio was close to the normal value of 1: 1. Such important population characteristics as normal sex ratio at the pupal stage and the high autogeny rate are indicative of high reproductive potential of the urban mosquito in St. Petersburg. The hydrotechnical (mostly drainage of basements) and special mosquito control measures are needed to decrease mosquito abundance and restrict their further dispersal within the city.