Shading by Napier grass reduces malaria vector larvae in natural habitats in western Kenya highlands
Wamae, P.M. ; Githeko, A.K. ; Menya, D.M. ; Takken, W. - \ 2010
EcoHealth 7 (2010)4. - ISSN 1612-9202 - p. 485 - 497.
anopheles-gambiae complex - sensu-stricto diptera - land-cover types - dar-es-salaam - spatial-distribution - microbial larvicides - oviposition site - culex mosquitos - aquatic stages - culicidae
Increased human population in the Western Kenya highlands has led to reclamation of natural swamps resulting in the creation of habitats suitable for the breeding of Anopheles gambiae, the major malaria vector in the region. Here we report on a study to restore the reclaimed swamp and reverse its suitability as a habitat for malaria vectors. Napier grass-shaded and non-shaded water channels in reclaimed sites in Western Kenya highlands were studied for the presence and density of mosquito larvae, mosquito species composition, and daily variation in water temperature. Shading was associated with 75.5% and 88.4% (P <0.0001) reduction in anopheline larvae densities and 78.1% and 88% (P <0.0001) reduction in Anopheles gambiae sensu lato (s.l.) densities in two sites, respectively. Shading was associated with a 5.7°C, 5.0°C, and 4.7°C, and 1.6°C, 3.9°C, and 2.8°C (for maximum, minimum, and average temperatures, respectively) reduction (P <0.0001) in water temperatures in the two locations, respectively. An. gambiae s.l. was the dominant species, constituting 83.2% and 73.1%, and 44.5% and 42.3%, of anophelines in non-shaded and shaded channels, respectively, in the two sites, respectively. An. gambiae sensu stricto (s.s.) constituted the majority (97.4%) of An. gambiae s.l., while the rest (2.6%) comprised of Anopheles arabiensis. Minimum water temperature decreased with increasing grass height (P = 0.0039 and P = 0.0415 for Lunyerere and Emutete sites, respectively). The results demonstrate how simple environmental strategies can have a strong impact on vector densities
The effect of water turbidity on the near-surface water temperature of larval habitats of the malaria mosquito Anopheles gambiae
Paaijmans, K.P. ; Takken, W. ; Githeko, A.K. ; Jacobs, A.F.G. - \ 2008
International Journal of Biometeorology 52 (2008)8. - ISSN 0020-7128 - p. 747 - 753.
western kenya - spatial-distribution - culicidae larvae - aquatic stages - sensu-lato - arabiensis diptera - giles complex - oviposition - survival - simulations
Water temperature is an important determinant in many aquatic biological processes, including the growth and development of malaria mosquito (Anopheles arabiensis and A. gambiae) immatures. Water turbidity affects water temperature, as suspended particles in a water column absorb and scatter sunlight and hence determine the extinction of solar radiation. To get a better understanding of the relationship between water turbidity and water temperature, a series of semi-natural larval habitats (diameter 0.32 m, water depth 0.16 m) with increasing water turbidity was created. Here we show that at midday (1300 hours) the upper water layer (thickness of 10 mm) of the water pool with the highest turbidity was on average 2.8 degrees C warmer than the same layer of the clearest water pool. Suspended soil particles increase the water temperature and furthermore change the temperature dynamics of small water collections during daytime, exposing malaria mosquito larvae, which live in the top water layer, longer to higher temperatures.
Observations and model estimates of diurnal water temperature dynamics in mosquito breeding sites in western Kenya
Paaijmans, K.P. ; Jacobs, A.F.G. ; Takken, W. ; Heusinkveld, B.G. ; Githeko, A.K. ; Dicke, M. ; Holtslag, A.A.M. - \ 2008
Hydrological Processes 22 (2008)24. - ISSN 0885-6087 - p. 4789 - 4801.
anopheles-gambiae diptera - aquatic stages - malaria transmission - culicidae larvae - land-cover - habitats - survival - highlands - reservoir - village
Water temperature is an important determinant of the growth and development of malaria mosquito immatures. To gain a better understanding of the daily temperature dynamics of malaria mosquito breeding sites and of the relationships between meteorological variables and water temperature, three clear water pools (diameter × depth: 0·16 × 0·04, 0·32 × 0·16 and 0·96 × 0·32 m) were created in Kenya. Continuous water temperature measurements at various depths were combined with weather data collections from a meteorological station. The water pools were homothermic, but the top water layer differed by up to about 2 °C in temperature, depending on weather conditions. Although the daily mean temperature of all water pools was similar (27·4-28·1 °C), the average recorded difference between the daily minimum and maximum temperature was 14·4 °C in the smallest versus 7·1 °C in the largest water pool. Average water temperature corresponded well with various meteorological variables. The temperature of each water pool was continuously higher than the air temperature. A model was developed that predicts the diurnal water temperature dynamics accurately, based on the estimated energy budget components of these water pools. The air-water interface appeared the most important boundary for energy exchange processes and on average 82-89% of the total energy was gained and lost at this boundary. Besides energy loss to longwave radiation, loss due to evaporation was high; the average estimated daily evaporation ranged from 4·2 mm in the smallest to 3·7 mm in the largest water pool