Effects of elevated temperatures on the development of immature stages of Anopheles gambiae (s.l.) mosquitoes

Objective This study investigated the effects of temperature on the development of the immature stages of Anopheles gambiae (s.l.) mosquitoes. Methods Mosquito eggs were obtained from laboratory established colonies and reared under eight temperature regimes (25, 28, 30, 32, 34, 36, 38 and 40 degrees C), and 80 +/- 10% relative humidity. Larvae were checked daily for development to the next stage and for mortality. Pupation success, number of adults produced and sex ratio of the newly emerged adults were recorded. Larval survival was monitored every 24 h, and data were analysed using Kaplan-Meier survival analysis. Analysis of variance was used where data followed normal distribution, and a Kruskal-Wallis test where data were not normally distributed. Larval and pupal measurements were log-transformed and analysed using ordinary least square regression with robust standard errors. Results Increasing the temperature from 25 to 36 degrees C decreased the development time by 10.57 days. Larval survival (X-2(6) = 5353.12, p < 0.001) and the number of adults produced (X-2(5) = 28.16, p < 0.001) decreased with increasing temperature. Increasing temperatures also resulted in significantly smaller larvae and pupae (p < 0.001). At higher temperatures, disproportionately more male than female mosquitoes were produced. Conclusions Increased temperature affected different developmental stages in the life cycle of An. gambiae (s.l.) mosquitoes, from larval to adult emergence. This study contributes to the knowledge on the relationship between temperature and Anopheles mosquitoes and provides useful information for modelling vector population dynamics in the light of climate change.