Some like it hot: a differential response to changing temperatures by the malaria vectors and s.l.

BACKGROUND

With the possible implications of global warming, the effect of temperature on the dynamics of malaria vectors in Africa has become a subject of increasing interest. Information from the field is, however, relatively sparse. We describe the effect of ambient temperature over a five-year period on the dynamics of and s.l., collected from a single village in southern Mozambique where temperatures varied from a night-time minimum of 6 °C in the cool season to a daytime maximum of 35 °C in the hot season.

RESULTS

Mean daily air temperatures varied from 34 °C to 20 °C and soil temperatures varied from 26 °C to 12 °C. Diurnal variation was greatest in the cooler months of the year and were greater in air temperatures than soil temperatures. During the study 301, 705 female were collected in 6,043 light-trap collections, 161, 466 in 7,397 exit collections and 16, 995 in 1,315 resting collections. The equivalent numbers for s.l. are 72,475 in light-traps, 33, 868 in exit collections and 5,333 from indoor resting collections. Numbers of mosquito were greatest in the warmer months. Numbers of s.l. went through a one hundredfold change (from a mean of 0.14 mosquitoes a night to 14) whereas numbers of merely doubled (from a mean of 20 to 40 a night). The highest environmental correlations and mosquito numbers were between mean air temperature ( = 0.52 for and 0.77 for s.l.). Numbers of mosquito collected were not related to rainfall with lags of up to four weeks. Numbers of both gravid and unfed complex females in exit collections continued to increase at all temperatures recorded but gravid females of decreased at temperatures above 28 °C. Overall the numbers of gravid and unfed collected in exit collections were not correlated ( = 0.07). For an unknown reason the number of s.l. fell below monitoring thresholds during the study.

CONCLUSIONS

Mean air temperature was the most important environmental parameter affecting both vectors in this part of Mozambique. Numbers of s.l. increased at all temperatures recorded whilst appeared to be adversely affected by temperatures of 28 °C and above. These differences may influence the distribution of the vectors as the planet warms.