Association Between Land Cover and Habitat Productivity of Malaria Vectors in Western Kenyan Highlands

Abstract

We examined the effects of land cover type on survivorship and productivity of Anopheles gambiae in Kakamega in the western Kenyan highlands (elevation = 1,420-1,580 meters above sea level). Under natural conditions, An. gambiae sensu lato adults emerged only from farmland habitats, with an estimated productivity of 1.82 mosquitoes/meter(2)/week, but not from forest and swamp habitats. To determine the effects of intraspecific competition and land cover types, semi-natural larval habitats were created within three land cover types (farmland, forest, and natural swamp), and three different densities of An. gambiae sensu stricto larvae were introduced to the larval habitats. The mosquito pupation rate in farmland habitats was significantly greater than in swamp and forest habitats, and larval-to-pupal development times were significantly shorter. At higher densities, the larvae responded to increased intraspecific competition by extending their development time and emerging as smaller adults, but initial larval density showed no significant effects on pupation rate. Land cover type may affect larval survivorship and adult productivity through its effects on water temperature and nutrients in the aquatic habitats, as shown by the significantly higher water temperature in farmland habitats, enhanced pupation rates and shortened development times from the addition of food to habitats, and a significant negative correlation of the occurrence of An. gambiae larvae with canopy cover and emergent plants in natural habitats. These results suggest that deforestation and cultivation of natural swamps in the western Kenyan highland create conditions favorable for the survival of An. gambiae larvae, and consequently increase the risks of malaria transmission to the human population.

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.…”

Integrated malaria vector control with microbial larvicides and insecticide-treated nets in western Kenya: a controlled trial

“…[9][10][11] While ITNs are currently the priority strategy, there is growing interest in attacking the aquatic stages of malaria vectors with microbial larvicides, in conjunction with environmental management. 5,6,[12][13][14][15][16][17][18][19][20][21] Presently, microbial larvicides are being used in an operational context only in Dar es Salaam, in the United Republic of Tanzania. 22,23 However, in the future larvicide application will be expanded to many of the 15 countries included in the President's Malaria Initiative and this interest is likely to spread to other African countries.…”

“…[1][2][3][4] The ecological features of the western highlands of Kenya support stable parasite transmission, and increasing population pressure has led to the clearance of natural swamps, massive deforestation and crop cultivation in the valley bottoms. 5,6 Because of these agricultural changes, many water bodies are now exposed to the sun and provide ideal conditions for vector proliferation and increased malaria transmission. 7 Malaria control in these highlands is based on insecticide-treated nets (ITNs), indoor-residual spraying (IRS) with insecticides and prompt and effective treatment of clinical malaria.…”

The value of georeferenced collection records for predicting patterns of mosquito species richness and endemism in the Neotropics

“…Changes in land cover and/or climate may have important effects on the distribution and intensity of mosquito-borne diseases on regional scales (e.g. Martens et ah, 1999;Lindsay & Bayoh, 2004;Zhou et al, 2004;Munga et al, 2006). Rubio-Palis and Zimmerman (1997) concluded that irrigation, clearing of tropical forest for subsistence agriculture, animal husbandry and mineral exploitation, and construction of dams complicate an ecoregional approach to classifying vector distribution in the Neotropics.…”