Population studies, physiological state and mortality factors of overwintering adult populations of females ofCulex pipiensL. (Diptera: Culicidae)

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Abstract
The biology of overwintering populations of adults ofCulex pipiensL. was studied between October 1977 and April 1980 in southern England. Data obtained from population studies showed that there was a rapid build-up at the beginning of hibernation in August, reaching a peak in late October-early November each year and gradually decreasing from December. Extensive movement both in and out and within the hibernation site occurred, with many individuals changing their locations or hibernacula during the course of hibernation. Studies on induced feeding showed that in the early months of hibernation (August-October) exposure to constant light for a minimum period of 12 days was required before the females would take a blood-meal. This period decreased during the course of hibernation. Observations on the physiological condition of hibernating females revealed that up to 90% of the population were inseminated. A few parous females entered hibernation shelters at the onset of winter but did not survive the winter. Furthermore, females used up about 80% of their fat food reserves during hibernation, while there was little or no change in the quantity of glycogen present. From an assessment of the impact of mortality factors on a population of known size, it was observed that exodus from the hibernation shelters accounted for about 30% reduction in the population size while depletion of food reserves and predation by spiders accounted for approximately 15 and 20% mortality, respectively.