Studies on hibernating populations of the mosquito Culex pipiens L. in southern and northern England

Summary

The population fluctuation of diapausing adult females Culex pipiens over-wintering in man-made shelters in southern and northern England was studied from 1967–71 and 1978–82, respectively. Females with well developed fat reserves started to enter hibernation sites in July and August, maximum numbers were reached in October–November, after which there was a large reduction in population so usually less than 10% of the population emerged from hibernation sites in April–May to begin the new spring generation. Spiders killed some hibernating adults. Although pathogenic fungi are known to cause large mortalities in some shelters, in the present ones such fungi were absent or very rare. However, in situations where predators and pathogens cause little mortality there is still a large loss of hibernating adults towards the end of hibernation. This mortality probably results from stresses caused by depletion of fat reserves, so in effect the mosquitoes die of ‘old age’.