A study of the age-composition of natural populations of Culex pipiens fatigans Wiedemann in relation to the transmission of filariasis due to Wuchereria bancrofti (Cobbold) in Ceylon.

Filariasis due to Wuchereria bancrofti is becoming an increasingly important problem in many countries of southern and south-eastern Asia. From 1962 to 1964, a study was made of the vector of this disease, Culex pipiens fatigans, in two districts of Colombo, Ceylon, one with vector control by larviciding and one without. Catches were made of the house-resting, biting and ovipositing populations, and the stages of ovarian development, parity and infection were determined by examination of the external appearance of the abdomen and dissection for ovariole dilatations and filariae. It was concluded that 10%-12% of the house-resting female population survived to the infective 2-parous stage and about 1.5% to the 3-parous stage. Daily mortality was estimated as 13%-24% for the district with vector control, and 18%-28% for that without. A field experiment based on the recapture of marked females confirmed these results. Biting took place indoors from 18.00 h to 06.00 h, with a single peak around midnight. Most females returned to feed directly from oviposition.