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Incorporating the effects of humidity in a mechanistic model of Anopheles gambiae mosquito population dynamics in the Sahel region of Africa.

Yamana TK, Eltahir EA - Parasit Vectors (2013)

Bottom Line: In this case, relative humidity had little effect on the mosquito population.In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.Future modeling work should account for these effects of relative humidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, MA 02139, USA. tkcy@mit.edu

ABSTRACT

Background: Low levels of relative humidity are known to decrease the lifespan of mosquitoes. However, most current models of malaria transmission do not account for the effects of relative humidity on mosquito survival. In the Sahel, where relative humidity drops to levels <20% for several months of the year, we expect relative humidity to play a significant role in shaping the seasonal profile of mosquito populations. Here, we present a new formulation for Anopheles gambiae sensu lato (s.l.) mosquito survival as a function of temperature and relative humidity and investigate the effect of humidity on simulated mosquito populations.

Methods: Using existing observations on relationships between temperature, relative humidity and mosquito longevity, we developed a new equation for mosquito survival as a function of temperature and relative humidity. We collected simultaneous field observations on temperature, wind, relative humidity, and anopheline mosquito populations for two villages from the Sahel region of Africa, which are presented in this paper. We apply this equation to the environmental data and conduct numerical simulations of mosquito populations using the Hydrology, Entomology and Malaria Transmission Simulator (HYDREMATS).

Results: Relative humidity drops to levels that are uncomfortable for mosquitoes at the end of the rainy season. In one village, Banizoumbou, water pools dried up and interrupted mosquito breeding shortly after the end of the rainy season. In this case, relative humidity had little effect on the mosquito population. However, in the other village, Zindarou, the relatively shallow water table led to water pools that persisted several months beyond the end of the rainy season. In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.

Conclusions: We proposed a new equation to describe Anopheles gambiae s.l. mosquito survival as a function of temperature and relative humidity. We demonstrated that relative humidity can play a significant role in mosquito population and malaria transmission dynamics. Future modeling work should account for these effects of relative humidity.

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Martens survival equation (left), RH stress index (center) and daily survival probability of mosquitoes using the newly developed formula (right).
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Figure 4: Martens survival equation (left), RH stress index (center) and daily survival probability of mosquitoes using the newly developed formula (right).

Mentions: Mosquito survival as a function of temperature and RH are shown for RHS = 42% and RHC = 5% is shown in Figure 4. RHS was set at 42% RH in order to reflect a decrease in longevity observed by Bayoh [6] at 40% RH compared to values ≥ 60% RH, and evidence that mosquitoes at 42% RH showed physiological signs of stress [7]. RHC was set at 5% as several of the desiccation studies found that RH < 10% killed all mosquitoes in one day [9,10]. While most of the experiments conducted to date relating mosquito survival to relative humidity and temperature focused on An. gambiae s.s., we make the assumption that our model is valid for the An. gambiae s.l. complex. However, parameter values can be adjusted to reflect regional or species-specific differences in tolerance to arid conditions, or based on improved knowledge on mosquito longevity at RH <40%.


Incorporating the effects of humidity in a mechanistic model of Anopheles gambiae mosquito population dynamics in the Sahel region of Africa.

Yamana TK, Eltahir EA - Parasit Vectors (2013)

Martens survival equation (left), RH stress index (center) and daily survival probability of mosquitoes using the newly developed formula (right).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3750695&req=5

Figure 4: Martens survival equation (left), RH stress index (center) and daily survival probability of mosquitoes using the newly developed formula (right).
Mentions: Mosquito survival as a function of temperature and RH are shown for RHS = 42% and RHC = 5% is shown in Figure 4. RHS was set at 42% RH in order to reflect a decrease in longevity observed by Bayoh [6] at 40% RH compared to values ≥ 60% RH, and evidence that mosquitoes at 42% RH showed physiological signs of stress [7]. RHC was set at 5% as several of the desiccation studies found that RH < 10% killed all mosquitoes in one day [9,10]. While most of the experiments conducted to date relating mosquito survival to relative humidity and temperature focused on An. gambiae s.s., we make the assumption that our model is valid for the An. gambiae s.l. complex. However, parameter values can be adjusted to reflect regional or species-specific differences in tolerance to arid conditions, or based on improved knowledge on mosquito longevity at RH <40%.

Bottom Line: In this case, relative humidity had little effect on the mosquito population.In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.Future modeling work should account for these effects of relative humidity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Massachusetts Institute of Technology, 15 Vassar Street, Cambridge, MA 02139, USA. tkcy@mit.edu

ABSTRACT

Background: Low levels of relative humidity are known to decrease the lifespan of mosquitoes. However, most current models of malaria transmission do not account for the effects of relative humidity on mosquito survival. In the Sahel, where relative humidity drops to levels <20% for several months of the year, we expect relative humidity to play a significant role in shaping the seasonal profile of mosquito populations. Here, we present a new formulation for Anopheles gambiae sensu lato (s.l.) mosquito survival as a function of temperature and relative humidity and investigate the effect of humidity on simulated mosquito populations.

Methods: Using existing observations on relationships between temperature, relative humidity and mosquito longevity, we developed a new equation for mosquito survival as a function of temperature and relative humidity. We collected simultaneous field observations on temperature, wind, relative humidity, and anopheline mosquito populations for two villages from the Sahel region of Africa, which are presented in this paper. We apply this equation to the environmental data and conduct numerical simulations of mosquito populations using the Hydrology, Entomology and Malaria Transmission Simulator (HYDREMATS).

Results: Relative humidity drops to levels that are uncomfortable for mosquitoes at the end of the rainy season. In one village, Banizoumbou, water pools dried up and interrupted mosquito breeding shortly after the end of the rainy season. In this case, relative humidity had little effect on the mosquito population. However, in the other village, Zindarou, the relatively shallow water table led to water pools that persisted several months beyond the end of the rainy season. In this case, the decrease in mosquito survival due to relative humidity improved the model's ability to reproduce the seasonal pattern of observed mosquito abundance.

Conclusions: We proposed a new equation to describe Anopheles gambiae s.l. mosquito survival as a function of temperature and relative humidity. We demonstrated that relative humidity can play a significant role in mosquito population and malaria transmission dynamics. Future modeling work should account for these effects of relative humidity.

Show MeSH
Related in: MedlinePlus