Spatial distribution and habitat characterisation of mosquito species in the lake and land habitats of western Kenya

Abstract

Background: Infections with mosquito-borne parasites are common in human
populations inhabiting tropical regions of the world. Malaria is endemic along Kenyan Lake Victoria basin and its vectors are fresh water breeders. However, much less is known about the current spatial distribution and habitat characterisation of mosquitoes including vectors of malaria in the lake waters and adjacent terrestrial aquatic habitats.
Objectives: To characterise mosquito larval habitats and to determine the spatial
distribution of mosquito species in lake and land habitats, measure aquatic habitats’ (water) physic-chemical parameters, enumerate the number of phytoplankton, zooplankton and fish species and determine their effects on the abundance of mosquitoes. This could allow larval control to be more effectively targeted at specific sites which in its turn could reduce malaria transmission in the area.
Design: Cross-sectional study.
Setting: The Kenyan Lake Victoria Basin.
Results: Anopheles and Culex species of mosquitoes were absent in different locations in the lake, but abundant in different aquatic habitats in different locations on land. There was heterogeneity in the relative abundance of Anopheles and Culex species in the aquatic habitats in different locations on land, p<0.001, Bartlett’s test. There were more Anopheles mosquito in quary and shoreline swamp puddles, flood plain, and stream edge puddles than natural swamps, rivers and permanent ponds habitats, P<0.001. There was no significant correlation of the abundance of Anopheles and physico-chemical parameters, P>0.05 (Pearsons correlation coefficiency). Also, there was no significant correlation between abundance of Anopheles mosquitoes and phytoplanktons, (P>0.05). Significant correlation was however, observed with Dinoflagellates on land, P=0.014. Clarias gariepinus were more insectivorous compared to Oreochromis niloticus, which mostly fed on zooplankton and food remains. The most abundant mosquitoes in the lake were Mansonia followed by Aedes species of mosquitoes.
Conclusion: Anopheles species of mosquitoes do not breed in deep permanent lake waters even if it is heavily infested by water hyacinth and other aquatic weeds. However, they breed in temporary or seasonal aquatic land habitats such as pools and swamps, more so when infested by aquatic and other vegetations. We recommend that, focus of malaria vector control should concentrate on land sites. Health education and awareness programs should be scaled up to inform the local communities on mosquito species ecology in relation to transmission of malaria and other mosquito- borne diseases. There is need to introduce certain fish species (Clarias gariepinus) for biological control of mosquitoes breeding in the aquatic habitats near human habitats.