Ecology and Management of Riceland Mosquitoes in Africa With Special Reference to Culex Quinquefasciatus

146 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007.The diverse mosquito species occurring in African rice agro-ecosystems have been scarcely studied despite the strong link between irrigated rice cultivation and mosquito-borne disease. Studies were conducted to determine the ecology of rice-land mosquitoes in Mwea rice agro-ecosystem, Kenya. In the first study, adult mosquitoes were collected indoors and outdoors to determine mosquito species diversity and abundance in relation to land use. Twenty-five mosquito species, dominated by Anopheles arabiensis, Culex quinquefasciatus, and Anopheles pharoensis, were collected. Species diversity and evenness indices were significantly higher in non-irrigated than irrigated agro-ecosystems. Conversely, mosquito densities were highest in planned rice agro-ecosystem and lowest in non-irrigated agro-ecosystem, demonstrating the impact of land use on mosquito species diversity and abundance. The second study involved larval sampling in irrigated rice and non-irrigated agro-ecosystems to determine the diverse aquatic habitats in which Culex mosquitoes thrive. Ten culicine species were collected, the main species being Culex duttoni and Cx. quinquefasciatus. Species richness and larval habitat diversity were significantly higher in non-irrigated than irrigated rice agro-ecosystem. The most productive habitats were not necessarily the most important for vector proliferation over space and time. Culex poicilipes was strongly associated with floating vegetation, Culex annulioris with clean water containing floating and emergent vegetation, and Cx. quinquefasciatus was associated with turbid water. The third study evaluated the effect of rice cropping cycle on mosquito species succession and abundance at the experimental rice plots. Nine mosquito species dominated by An. arabiensis, Cx. quinquefasciatus, An. pharoensis and Ficalbia splendens, thrived in the rice fields. The rice cropping cycle had a significant impact on seasonal fluctuations in mosquito species composition and abundance. Dissolved oxygen, number of tillers and rice height were significant negative predictors of An. arabiensis and Cx. quinquefasciatus larvae. In addition, Cx. quinquefasciatus was also negatively associated with water depth and positively with turbidity. The fourth study was also conducted at the experimental plots to determine the relationship between insect predators and mosquito larvae. Out of the 15 insect families observed, Libellulidae and Coenagrionidae were negatively associated with An. arabiensis larvae and Dytiscidae and Coenagrionidae were negatively associated with Cx. quinquefasciatus larvae. Lastly, four sampling techniques were evaluated for their efficiency in outdoor collection of Cx. quinquefasciatus and other rice-land mosquitoes. CO2-baited CDC light traps were superior to non-baited CDC light traps in collection of Cx. quinquefasciatus and Culex annulioris. More Cx. quinquefasciatus females were collected in grass infusion-baited gravid traps than egg rafts of this species in oviposition traps containing the same infusion. The majority of mosquitoes in CDC light trap collections were unfed but in contrast, most of those collected in gravid traps were gravid, indicating the need to supplement light traps with gravid traps especially in arboviral surveys. Collectively, these findings provide useful information that can guide the formulation and implementation of an integrated vector control program.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD