Stable and fluctuating temperature effects on the development rate and survival of two malaria vectors, Anopheles arabiensis and Anopheles funestus

Background: Understanding the biology of malaria vector mosquitoes is crucial to understanding many aspects of the disease, including control and future outcomes. The development rates and survival of two Afrotropical malaria vectors, Anopheles arabiensis and Anopheles funestus, are investigated here under conditions of constant and fluctuating temperatures. These data can provide a good starting point for modelling population level consequences of temperature change associated with climate change. For comparative purposes, these data were considered explicitly in the context of those available for the third African malaria vector, Anopheles gambiae. Methods: Twenty five replicates of 20-30 eggs were placed at nine constant and two fluctuating temperatures for development rate experiments and survival estimates. Various developmental parameters were estimated from the data, using standard approaches. Results: Lower development threshold (LDT) for both species was estimated at 13-14 degrees C. Anopheles arabiensis developed consistently faster than An. funestus. Optimum temperature (T-opt) and development rate at this temperature (mu(max)) differed significantly between species for overall development and larval development. However, T-opt and mu(max) for pupal development did not differ significantly between species. Development rate and survival of An. funestus was negatively influenced by fluctuating temperatures. By contrast, development rate of An. arabiensis at fluctuating temperatures either did not differ from constant temperatures or was significantly faster. Survival of this species declined by c. 10% at the 15 degrees C to 35 degrees C fluctuating temperature regime, but was not significantly different between the constant 25 degrees C and the fluctuating 20 degrees C to 30 degrees C treatment. By comparison, previous data for An. gambiae indicated fastest development at a constant temperature of 28 degrees C and highest survival at 24 degrees C. Conclusions: The three most important African malaria vectors all differ significantly in development rates and survival under different temperature treatments, in keeping with known distribution data, though differences among M and S molecular forms of An. gambiae likely complicate the picture. Increasing temperatures associated with climate change favour all three species, but fluctuations in temperatures are detrimental to An. funestus and may also be for An. gambiae. This may have significant implications for disease burden in areas where each species is the main malaria vector.