The Dynamics of an Adult Population of Aedes aegypti in Relation to Dengue Haemorrhagic Fever in Bangkok

(1) An adult population of Aedes aegypti was studied in the residential compound of a Buddhist temple, Wat Samphaya, in Bangkok. The objectives of the study were to measure possible changes in population size, survival rate and movement throughout the year in order to test the hypothesis that fluctuations in these parameters accounted for the resurgence of A. aegypti-transmitted dengue haemorrhagic fever during the wet season. Concurrent studies were made of larval populations both in Wat Samphaya and elsewhere in and around Bangkok. (2) Mark-release-recapture techniques were used for estimating the adult population parameters. Each wild-caught mosquito before release was etherized and given a unique number by marking with spots of quick-drying paint on the wings and/or thorax. (3) A comparison of the amount of blood in the stomach and the ovarian condition of individual females recaptured on more than one occasion showed little correlation between the feeding pattern and ovarian development. The presence of fresh blood in a proportion of gravid and semi-gravid females made it impractical to score their ovarian stage unequivocably without dissection. Consequently, it proved impossible to measure the average length of the gonotrophic cycle in the wild population. (4) Dispersal of individual mosquitoes was studied by observing the distance each had moved between release and subsequent recapture. Both sexes tended to move further in the first 24-h period after release than later, perhaps because of the effects of handling. There was no evidence of an effect of the time of the year on the amount of movement, nor was there any difference in this respect between the sexes. Although it was found that males moved more than females in the first 24 h, the females lived longer and therefore ultimately moved at least as far. It was estimated that only about 40% of individuals released at random in the study area (94 X 56 m) remained there after 24 h. Taking into account this loss, the mean distance moved by mosquitoes in 24 h was estimated to be 37 m. Despite this movement, the mosquitoes were not randomly distributed among the rooms, probably owing to some rooms being more attractive than others rather than to a non-random distribution of breeding places. (5) The 24-h survival rate using the model developed by Fisher & Ford (1947), averaged over 12 months, was 0.70 for males and 0.81 for females. There was no significant difference in the values between months but th