Studies on the development and survival of anopheles gambiae sensu stricto at various temperatures and relative humidities

Abstract

Anopheles gambiae sensu stricto is the most efficient malaria vector in Africa. Recent advances in mapping the distribution of this vector have exploited the relationship between climatic factors and vector parameters such as growth, survival and reproduction. This work was designed to investigate the effect of temperature and humidity on the development and survival of the vector and to test the use of recently developed tools in describing its distribution. The development rate and survival of the aquatic stages of the vector were investigated at 16 constant temperatures. Adults were produced between 16 -34ºC with a peak development rate at 28ºC and peak number of adults at 22 -26ºC. Larvae survived for less than 7 days at 10º, 12º, 38 º, and 40ºC but for more than 5 weeks, at 14-18ºC without any development of adults. Laboratory models accurately predicted development times at natural breeding sites in The Gambia suggesting the applicability of the models to field situations. The survival and mortality rates of adult An. gambiae s.s. were monitored at combinations of temperatures from 0-45ºC at 5 intervals and 40%, 60%, 80% and 100% relative humidity. Survival was highest at 15-25ºC and 60-100% relative humidity. The temperature - larva development relation was used to produce a distribution map across Africa while climatic data from sites at which chromosomal forms of the insect have been found were used to map the distribution of the forms across West Africa. Climate is an important determinant of insect distribution and the use of climate and vector parameters in describing or predicting vector and disease distribution will provide a cheaper and less labour intensive tool than traditional methods.