Life-Table Analysis of Anopheles arabiensis in Western Kenya Highlands: Effects of Land Covers on Larval and Adult Survivorship

Abstract

In high-elevation areas in western Kenya, the abundance of Anopheles arabiensis is either very low or absent. The western Kenya highlands (an area with an elevation > 1,500m above sea level) have also been experiencing extensive deforestation, and deforestation has been suggested as one of the important factors that facilitate malaria transmission in the highlands. This study investigated whether climate conditions in the western Kenya highlands (Kakamega, elevation 1,500 m above sea level) were permissive to the development and survival of An. arabiensis and whether deforestation promoted An. arabiensis survivorship of immature and adult stages, using life-table analysis. We found that in larval habitats located in forested areas, only 4-9% of first-instar larvae developed into adults and the development length exceeded 20 days. Mean water temperature of aquatic habitats in the deforested area was 4.8-6.1 degrees C higher than that in the forested area, larval-to-adult survivorship was increased to 65-82%, and larval-to-adult development time was shortened by 8-9 days. The average indoor temperature in houses in the deforested area was 1.7-1.8 degrees C higher than in the forested area, and the relative humidity was 22-25% lower. The median survival time of adult mosquitoes in the deforested area was 49-55% higher than those in the forested area. The net reproductive rate of female mosquitoes in the deforested area was 1.7- to 2.6-fold higher than that in the forested area. Compared with previously published data on An. gambiae, the net reproductive rate of An. arabiensis was only 0.8-1.3% of Anopheles gambiae in the forested area and 2.3-2.6% in the deforested area. Therefore, the current ambient climate condition is less permissive to An. arabiensis than to An. gambiae in western Kenya highlands. However, environmental changes such as deforestation and global warming may facilitate the establishment of An. arabiensis populations in the highlands.

Modeling the Relationship between Precipitation and Malaria Incidence in Children from a Holoendemic Area in Ghana

“…The abundance of water bodies and favorable temperatures, maize plantings, extensive deforestation, or farmland have been associated with increased larval or mosquito abundance and thus increased risk for malaria transmission in human populations. [31][32][33][34] Other studies have used geographic information systems and satellite imagery to investigate environmental factors that potentially drive the dynamics of malaria vector populations [34][35][36] and other vector-borne and zoonotic diseases such as dengue fever or hantavirus. [37][38][39] It has been shown that the efficacy of control measures such as intermittent preventive treatment (IPT) can be strongly dependent on the present malaria incidence, [40][41][42] and it can be assumed that direct and contextual effects increase with malaria risk after an intervention.…”

Malaria Transmission in the African Highlands in a Changing Climate Situation: Perspective from Kenyan Highlands

“…We found that deforestation increased the indoor mean temperature by 1.8 0 C. Mean maximum and minimum temperatures were increased by 2.3 0 C and 1.5 0 C respectively. Outdoor temperatures were increased by 0.5 0 C. The mean indoor relative humidity in the deforested area was about 22.6% lower than in the forest area during the dry season (79.88% vs. 57.29%) (Afrane et al 2005;Afrane et al 2006;Afrane et al 2008;Afrane et al 2007). Temperature and humidity were measured in houses in study sites that were originally forest but large portions of it have been deforested.…”

“…Adult An. arabiensis placed in houses in the deforested area had an enhanced survival and better reproductive fitness than those in the forested area (Afrane et al 2007). The implications of these findings are that, if the current trends of deforestation continue in the highlands, there could be a three vector system in the highlands, instead of the current two.…”

The biology and demographic parameters of Aedes albopictus in northern peninsular Malaysia

“…Most of studies have used laboratory data collected under controlled conditions, known to provide maximal growth potentials that may not occur in nature [15] . Recently, a few entomologists have attempted utilizing field data for the development of life tables of Anopheles mosquitoes [16] .…”