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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/meter2/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.
Received August 2, 2005. Accepted for publication September 1, 2005.
Acknowledgments: We thank Maurice Okonji, Stephen Ajuma, Peter A. Lutiali, Wilberforce Miheso, and Amos Wabwile for technical assistance, and Sarah Gage and anonymous reviewers for valuable suggestions and critics. This paper is published with the permission of the Director of the Kenya Medical Research Institute.
Financial support: This work was supported by National Institutes of Health grants R01 AI-50243 and D43 TW01505.
* Address correspondence to Guiyun Yan, Department of Biological Sciences, State University of New York, Buffalo, NY 14260. E-mail: gyan{at}buffalo.edu
Authors’ addresses: Stephen Munga, Emmanuel Mushinzimana, and Andrew K. Githeko, Kenya Medical Research Institute, Kisumu, Kenya, E-mails: smunga{at}kisian.mimcom.net, emushinzimana{at}kisian.mimcom.net, and agitheko{at}kisian.mimcom.net. Noboru Minakawa, Faculty of Medicine, Saga University, 5-1-1 Nabeshima, Saga 849-8501, Japan, E-mail: minakawa{at}post.saga-med.ac.jp. Guofa Zhou and Guiyun Yan, Department of Biological Sciences, State University of New York, Buffalo, NY 14260, E-mails: gzhou2{at}acsu.buffalo.edu and gyan{at}buffalo.edu. Okeyo-Owuor J. Barrack, School of Environmental Studies, Moi University, Eldoret, Kenya, E-mail: viredresearch{at}yahoo.com.
Reprint requests: Guiyun Yan, Department of Biological Sciences, State University of New York, Buffalo, NY 14260.
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