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Diversity of Riceland Mosquitoes and Factors Affecting Their Occurrence and Distribution in Mwea, Kenya Author(S): Ephantus J

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Diversity of Riceland Mosquitoes and Factors Affecting Their Occurrence and Distribution in Mwea, Kenya Author(S): Ephantus J Diversity of Riceland Mosquitoes and Factors Affecting Their Occurrence and Distribution in Mwea, Kenya Author(s): Ephantus J. Muturi, Josephat I. Shililu, Benjamin G. Jacob, Joseph M. Mwangangi, Charles M. Mbogo, John I. Githure, and Robert J. Novak Source: Journal of the American Mosquito Control Association, 24(3):349-358. 2008. Published By: The American Mosquito Control Association DOI: http://dx.doi.org/10.2987/5675.1 URL: http://www.bioone.org/doi/full/10.2987/5675.1 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/page/ terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. Journal of the American Mosquito Control Association, 24(3):349–358, 2008 Copyright E 2008 by The American Mosquito Control Association, Inc. DIVERSITY OF RICELAND MOSQUITOES AND FACTORS AFFECTING THEIR OCCURRENCE AND DISTRIBUTION IN MWEA, KENYA EPHANTUS J. MUTURI,1 JOSEPHAT I. SHILILU,2,3 BENJAMIN G. JACOB,1 JOSEPH M. MWANGANGI,4 CHARLES M. MBOGO,4 JOHN I. GITHURE2 AND ROBERT J. NOVAK1 ABSTRACT. Knowledge of mosquito species diversity, occurrence, and distribution is an essential component of vector ecology and a guiding principle to formulation and implementation of integrated vector management programs. A 12-month entomological survey was conducted to determine the diversity of riceland mosquitoes and factors affecting their occurrence and distribution at 3 sites targeted for malaria vector control in Mwea, Kenya. Adult mosquitoes were sampled indoors by pyrethrum spray catch and outdoors by the Centers for Disease Control and Prevention light traps. Mosquitoes were then morphologically identified to species using taxonomic keys. The characteristics of houses sampled for indoor resting mosquitoes, including number of people sleeping in each house the night preceding collection, presence of bed nets, location of the house, size of eaves, wall type, presence of cattle and distance of the house to the cowshed, and proximity to larval habitats, were recorded. Of the 191,378 mosquitoes collected, 95% were identified morphologically to species and comprised 25 species from 5 genera. Common species included Anopheles arabiensis (53.5%), Culex quinquefasciatus (35.5%), An. pharoensis (4.7%), An. coustani (2.5%), and An. funestus (1.6%). Shannon’s species diversity and evenness indices did not differ significantly among the 3 study sites. There was a marked house-to-house variation in the average number of mosquitoes captured. The number of people sleeping in the house the night preceding collection, size of eaves, distance to the cowshed, and the nearest larval habitat were significant predictors of occurrence of either or both An. arabiensis and Cx. quinquefasciatus. The peak abundance of An. arabiensis coincided with land preparation and the first few weeks after transplanting of rice seedlings, and that of Cx. quinquefasciatus coincided with land preparation, late stage of rice development, and short rains. After transplanting of rice seedlings, the populations of Cx. quinquefasciatus were collected more outdoors than indoors, suggesting a shift from endophily to exophily. These results demonstrate that irrigated rice cultivation has a strong impact on mosquito species occurrence, distribution, abundance, and behavior, and that certain house characteristics increase the degree of human–vector contact. KEY WORDS Irrigation, rice, mosquito species, mosquito-borne disease INTRODUCTION al. 1999), Bancroftian filariasis (Mawuli et al. 1999), and arboviruses (Diallo et al. 2005). In most African countries, human population In order to minimize the risk of mosquito-borne growth outpaces agricultural production (Voros- diseases and associated economic loss in irrigated marty et al. 2000). In an effort to boost food areas, there is an urgent need to control mosquito production to feed this population, water devel- vectors. Integrated vector management (IVM) is opment projects have been introduced and the considered the best approach of reducing mosquito area under irrigated agriculture extended (Keiser densities, especially in a rice agro-village complex et al. 2004). Unfortunately, irrigated agriculture, where large bodies of water exist (Lacey and Lacey especially rice cultivation, creates aquatic habitats 1990). The concept of integrated pest management that support prodigious numbers of diverse was first proposed by Stern et al. (1959) for mosquito species, including vectors of malaria, management of crop pests but is also adaptable to filariasis, and arboviruses as well as nuisance arthropod public health pests (Metcalf and Novak species (Muturi et al. 2006). As a result, 1994). As an applied ecological approach, IVM numerous studies have demonstrated a strong relies on packages of evidence-based interventions, link between irrigation development and in- tailored to suit the local settings to control, creased prevalence of malaria (Ghebreyesus et manage, and monitor vector-borne diseases at all relevant points in the life cycle and transmission 1 Department of Medicine, William C. Gorgas Center cycle of the vector, with minimum negative effect for Geographic Medicine, University of Alabama at on the environment and human health (Novak and Birmingham, Birmingham, AL 35294. Lampman 2001). In particular, IVM requires 2 Human Health Division, International Centre of proper understanding of the complex interrelations Insect Physiology and Ecology, PO Box 30772 Nairobi, between various components of disease transmis- Kenya. 3 sion (Metcalf and Novak 1994). Studies have Department of Zoology, Jomo Kenyatta University shown that even within a single community, there of Agriculture and Technology, PO Box 62000 Nairobi, Kenya. exists house-to-house variation in mosquito densi- 4 Centre for Geographic Medicine Research-Coast, ties and degree of disease transmission as a result Kenya Medical Research Institute, PO Box 428 Kilifi, of differences not only in characteristics of the Kenya. houses and their inhabitants but also in levels of 349 350 JOURNAL OF THE AMERICAN MOSQUITO CONTROL ASSOCIATION VOL.24,NO.3 elevation, water table, and proximity to larval village. Rurumi is located northwest of the habitats and alternative hosts (Minakawa et al. scheme and has 261 homesteads and more than 2002, Rwegoshora et al. 2007). Identifying the 920 residents. Cows, goats, chickens, and donkeys driving forces that determine when and where a are the primary domestic animals in all 3 villages. particular mosquito species occurs is therefore an These animals are kept within 5 m of most essential component of mosquito-borne disease houses. More than 90% of the houses are management. semipermanent, with mud walls and iron roofing. Most entomological studies in East African rice More than 75% of each village land is under rice agro-ecosystems have mainly focused on major cultivation and human habitation occupies the malaria vectors with little attention to other remaining area, with less than 10% utilized for mosquito species. The only detailed studies on vegetables and bananas. The rice cropping riceland mosquito species diversity are those by schedule in these villages is guided by the water Chandler and Highton (1975, 1976), Chandler et distribution scheme as determined by the Nation- al. (1975, 1976), and Surtees et al. (1970) in Ahero al Irrigation Board. Many species of birds and Rice Scheme, Muturi et al. (2006) in Mwea Rice mammals in the surrounding areas visit the rice Scheme, Kenya, and Ijumba et al. (2002) in lower fields for feeding and are generally considered as Moshi, Tanzania. The paucity of information on temporary or ephemeral inhabitants that can act riceland mosquito species diversity has made as intermediate hosts for arboviruses. formulation and implementation of IVM pro- grams difficult. The result has been emergence Rice cropping practice of arboviral diseases previously thought to be effectively controlled or unimportant (Gubler The typical rice farming practices include land 1996) and changes in transmission dynamics of preparation, nursery preparation, transplanting, malaria and Bancroftian filariasis (Keiser et al. fertilizer application, field maintenance, prehar- 2004, Erlanger et al. 2005). vesting drainage, and harvesting. Land prepara- Identifying diverse mosquito species occurring tion begins in July and involves flooding, rotava- in a riceland agro-ecosystem is an essential pre- tion, and leveling of the paddies, followed by requisite for understanding the ecology of disease nursery sowing. Transplanting is usually done 4 vectors, which is the guiding principle for imple- wk after nursery sowing (August). The level of mentation of an IVM program. The objective of water in the paddies is increased to a depth of this
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