Population dynamics,age composition and survival of Downsiomyia nivea in relation to transmission of diurnally subperiodic filariasis

Diurnally subperiodic Wuchereria bancrofti (DSPWB) filariasis is transmitted by the Downsiomyia nivea. In India, it is prevalent only in the Nicobar district of Andaman and Nicobar Islands. Knowledge of the population dynamics and bio-ecology of vectors is crucial to develop intervention measures. Entomological studies were performed for 12 months by collecting mosquitoes that landed on human baits for feeding in Teressa Island. Age composition, mosquitoes that had laid eggs at least once, finite rate of natural increase (λ) and vector survival reflecting the population dynamics of Do. nivea in relation to transmission of filariasis were estimated. A total of 3625 Do. nivea were collected. Changes in finite rate of increase (λ > 1) during favorable months indicate an increase in the vector population, suggesting the need for intensified intervention. The proportion of mosquitoes completing more than one gonotrophic cycle was higher in months when λ was 1. Do. nivea abundance and its parous densities varied with seasons. Survival of Do. nivea (indicated by the proportion of parous mosquitoes) was lower in the pre-monsoon season than during the monsoon and post-monsoon seasons. The probability of the daily survival of Do. nivea through one gonotrophic cycle was 0.75, with a declining trend as age increased. The maximum transmission of DSPWB occurred during the pre-monsoon, followed by the late monsoon, post-monsoon and monsoon seasons. Perennial transmission is evident. Therefore intervention measures must be planned throughout the year. Prospects of vector control are limited due to the cryptic breeding and diurnal biting habits. Mass chemotherapy with a single dose of an antifilarial drug is a potential option for control.