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The purpose of this study was to determine the ecology of the common arboviral mosquito vectors in Mombasa, Kilifi and Malindi urban areas of coastal Kenya. Mosquito larvae were collected using standard dippers and pipettes. Egg survivorship in dry soil was evaluated by collecting soil samples from dry potential larval developmental sites, re-hydrating them for hatching and rearing of the eventual larvae to adults. Adult mosquitoes were collected with CDC light traps and BG-Sentinel traps. All blood-fed females were tested for bloodmeal origin. Mosquitoes were screened for arboviruses using RT-qPCR. Overall, the predominant species were Culex quinquefasciatus(Say) 72.4% (n= 2,364) and Aedes aegypti(L.), 25.7%, (n= 838). A total of 415 larval developmental sites were identified indoors (n= 317) and outdoors (n= 98). The most productive larval developmental sites, both indoors and outdoors, were assorted small containers, water tanks, drainages, drums, and jerricans. Overall, 62% (n= 18) of the soil samples collected were positive for larvae which were used as a proxy to measure the presence of eggs. The mosquitoes fed on humans (29.8%) and chickens (3.7%). Of 259 mosquitoes tested for viral infection, 11.6% were positive for Flavivirusonly. The most productive larval developmental sites for arboviral vectors indoors were small containers, water tanks, jerricans, and drums whereas small containers, water tanks, drainage channels, buckets, tires, and water troughs were the productive larval developmental sites outdoors.

Field studies were conducted in a rice, Oryza sativa L., agroecosystem in Mwea Kenya to compare the efficiency of CO2-baited Centers for Disease Control (CDC) light traps against nonbaited CDC light traps and gravid traps against oviposition traps in outdoor collection of Culex quinquefasciatus Say (Diptera: Culicidae) and other mosquitoes. Collectively, 21 mosquito species from the genera Culex, Anopheles, Mansonia, Ficalbia, and Aedes were captured during the 10-wk study period. Cx. quinquefasciatus was the predominant species in all trap types with proportions ranging from 57% in the nonbaited CDC light traps to 95% in the gravid traps. Significantly higher numbers of Cx. quinquefasciatus and Culex annulioris Theobald were collected in the CO2-baited CDC light traps than in the nonbaited CDC light traps, but the numbers of other mosquito species, including malaria vectors Anopheles arabiensis Patton and Anopheles funestus Giles did not differ significantly between the two trap types. 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. Although most mosquitoes captured in CO2-baited and nonbaited CDC light traps were unfed, most of those collected in gravid traps were gravid. From these findings, it is concluded that at least in the rice-growing area of Mwea Kenya, CO2-baited CDC light traps in conjunction with gravid traps can be used in monitoring of Cx. quinquefasciatus both for control and disease surveillance.

The succession of mosquito species and abiotic factors affecting their distribution and abundance in rice (Oryza spp.) fields was investigated over a 16-wk rice growing cycle covering the period between January and May 2006. Fifteen experimental rice plots were sampled for mosquito larvae and characterized based on rice height, number of tillers, floating vegetation cover, water depth, water temperature, turbidity, salinity, pH, dissolved oxygen, total dissolved solids, and conductivity. Microscopic identification of 3,025 larvae yielded nine mosquito species predominated by Anopheles arabiensis Patton (45.0%), Culex quinquefasciatus Say (35.8%), Anopheles pharoensis Theobald (9.0%) and Ficalbia splendens Theobald (7.1%). Other species, including Anopheles rufipes Gough, Anopheles coustani Laveran, Anonopheles maculipalpis Giles, Culex annulioris Theobald, and Culex poicilipes Theobald made up 3.1% of the total collection. Anopheles gambiae s.l., Cx. quinquefasciatus, and An. pharoensis occurred throughout the cycle, but they were more abundant up to 4 wk posttransplanting with peaks after fertilizer application. As rice plants became established, three groups of mosquitoes were recognized: the first groups included An. rufipes, Fl. splendens, and Cx. annulioris, which occurred throughout much of the second half of the rice cycle, whereas the second group included Cx. poicilipes, which was found in the middle of the rice cycle. An. coustani and An. maculipalpis formed the third group occurring toward the end of the cycle. Dissolved oxygen, number of tillers, and rice height were negatively associated with the abundance of An. arabiensis and Cx. quinquefasciatus larvae. In addition, Cx. quinquefasciatus also was associated with water depth (-ve) and turbidity (+ve). Abundance of An. pharoensis larvae was significantly associated with water temperature (+ve), the number of tillers (-ve), and rice height (-ve), whereas Fl. splendens was significantly associated with the number of tillers (+ve). The results demonstrate a complex nature of the interactions between some of the factors in the ecosystem and mosquito species abundance and calls for time-dependent and species-specific mosquito control operations.