Influence of indoor microclimate and diet on survival of Anopheles gambiae s.s. (Diptera: Culicidae) in village house conditions in western Kenya

Abstract

The survival of female Anopheles gambiae s.s. mosquitoes inside two village house types (grass-thatched and iron-roofed) was studied in relation to diet and ambient indoor microclimatic conditions. Two batches of 20–30, 1-day-old laboratory-bred mosquitoes were maintained inside cages in the grass-thatched (n = 2) and iron-roofed (n = 2) houses and fed daily, one group on 10% glucose and the other on human blood. Throughout the experiments, indoor temperature and relative humidity of the houses were recorded, and mortality of mosquitoes monitored daily until all had died. The experiments were replicated thrice. There was no significant variation in the overall mean temperature (P = 0.93) or relative humidity profiles (P = 0.099) between the two house types, although the iron-roofed houses recorded higher temperature peaks. A Kaplan-Meier survival analysis showed that the mean survival times of mosquitoes were 8 and 10 days in the two grass-thatched huts and 7 and 10 days in the two iron-roof houses for mosquitoes feeding on blood and sugar meals, respectively. The mean survival times of mosquitoes maintained inside similar house types differed only due to diet. In the proportionality of hazards model (Cox regression), the dietary regimes significantly influenced the probability of survival (P = 0.0001), with mosquitoes surviving longer on sugar meals than on blood. Microclimatic factors inside houses also significantly influenced mosquito survival. Although higher peak temperatures were recorded in corrugated iron-roofed houses, the survival of the mosquitoes resting in them did not differ significantly from that in grass-thatched houses. However, the impact of these temperatures on the development of malaria parasites inside the vector needs to be investigated.