Competitive interactions between larvae of the malaria mosquitoes Anopheles arabiensis and Anopheles gambiae under semi-field conditions in western Kenya
Paaijmans, K.P. ; Huijben, S. ; Githeko, A.K. ; Takken, W. - \ 2009
Acta Tropica 109 (2009)2. - ISSN 0001-706X - p. 124 - 130.
aedes-aegypti diptera - polymerase chain-reaction - interspecific competition - triseriatus diptera - container mosquitos - albopictus diptera - growth-retardant - culicidae larvae - complex - temperature
The present paper reports the occurrence of competition between larvae of the malaria mosquito sibling species Anopheles arabiensis and An. gambiae under ambient conditions in western Kenya. Larvae of both species were reared at the same density and under the same food conditions outdoors in single-species and mixed-species populations (species ratio 1:1) in transparent cups that floated in small and large semi-natural pools, which experienced different diurnal variations in water temperature. In a second experiment, both species were reared at similar densities and under the same food conditions in trays in either single-species or mixed-species populations at different proportions (species ratio 1:1, 1:3 or 3:1). Competition affected the development rate of both species in an opposite way: the development time of larvae of An. arabiensis increased whereas the development time of larvae of An. gambiae decreased in the presence of its sibling species. In small pools larvae developing in mixed-species populations experienced a higher mortality than larvae reared in single-species populations, whereas no such effect was observed in the large pools. In both species the time to pupation was longer and emerging females were larger in the small pools. Larval mortality of An. arabiensis was lower in the small pools compared to the large pools, whereas An. gambiae showed the opposite trend. Overall An. arabiensis showed reduced development rates, higher mortality rates and emerged with a larger body size compared to An. gambiae. The implication of these competitive interactions between larvae of An. arabiensis and An. gambiae under semi-filed conditions needs to be considered in the design and implementation of programmes that aim to reduce malaria transmission as competition may alter the species composition in the field.
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
The effects of food and space on the occurrence of cannibalism and predation among larvae of Anopheles gambiae s.l.
Koenraadt, C.J.M. ; Majambere, S. ; Hemerik, L. ; Takken, W. - \ 2004
Entomologia Experimentalis et Applicata 112 (2004). - ISSN 0013-8703 - p. 125 - 134.
aedes-aegypti - giles complex - kisumu area - body-size - interspecific competition - intraspecific competition - growth retardant - culicidae larvae - sensu-stricto - species-b
Competitive interactions among the aquatic stages of the malaria mosquito Anopheles gambiae s.l. (Diptera: Culicidae) may affect the resulting adult densities and, hence, the risk of malaria. We investigated the impact of the presence of a fourth-instar larva (An. gambiae Giles s.s. or An. arabiensis Patton), the quantity of food, and the available space on the survival and development of freshly hatched larvae of An. gambiae s.s. and An. arabiensis. To analyse the results, two proportional hazard models were constructed. The first estimated the effects of all covariates on mortality rate and the second estimated the effects of the covariates on development rate into the third larval instar (L3). A time-dependent covariate for density, which changed during the experiment as a result of death or development to L3, was included in both models. In the presence of a fourth-instar larva (L4), survival of the experimental larvae was significantly reduced, but no difference was detected between the presence of L4 An. gambiae and L4 An. arabiensis. The observation that the majority of dead larvae were not recovered in trays with an L4 present suggested that cannibalism and predation occurred readily. Limitation in space significantly increased mortality of larvae, whereas a limitation of food reduced larval development rate, but did not cause mortality per se. From this, we concluded that both cannibalism and predation were enhanced as a result of more frequent interactions within smaller environments, but did not occur for reasons of food shortage. This study shows that inter- and intraspecific interactions among larvae of the An. gambiae complex strongly affect survival and development, and that the quantity of food and the available space are important determinants of the outcome of these interactions. Implications of the results are discussed with respect to the population dynamics of both malaria vectors in the field.