Faunistic Study on Species Composition of Mosquitoes and Sand Flies around Mrima Hill a High Radiation Area in Kwale County, Kenya

Mrima hill in Kwale County, along the Kenyan Indian Ocean coast, is known to have high natural background radiation caused mainly by 232Thorium. Despite other parts of the coast having been studied for human disease vectors including mosquitoes and phlebotomine sand flies, no studies have been carried out around Mrima hill to establish the prevalence of these important insects. The aim of this study was to investigate and establish mosquito and sand fly species diversity as well as possible infections. Thirty eight houses were randomly selected and sampled for radiation using Digilert 100 CPMS reader. Light traps were used to trap the insects around houses set at 0600 pm and collected at 0600 am. All females were dissected and examined microscopically for parasites. Mosquitoes and mounted sand flies were identified using standard taxonomic keys. All the numbers were recorded and Data analyzed using SPSS utilizing chi-square and Pearson correlation. A total of 131 mosquitoes and 39 sand flies were caught. Apart from Aedes aegypti (1.9%) which is of medical importance, the other mosquito species caught were Culex pipiens (69.42%), Cx. vansomerenae (1.5%) and Mansonia uniformis (9.6%). Sand flies caught were Sergentomyia bedfordi (74.36%), S. suberecta (15.35%), S. meilloni (5.12%), S. schwetzi (2.56%) and S. inermis (2.56%). None of these are of medical importance. The highest radiation level recorded was 17.5 mlliSieverts/year wheras the lowest was 5.9 mSv/yr, with a mean radiation of 10.52 m Sv/yr. There was no significant relationship between radiation levels number of mosquitoes (x2=103.7, df=99, P=0.353) or sand flies (x2=40.0, df=55, P=0.936). There was also no significant relationship between numbers of mosquitoes and sand flies (x2=36, P=0.165) and also no correlation between radiation levels and elevation (r = -0.389, df=10, P=0.211). It can be concluded from the results that it is unlikely that the insect-borne diseases can occur around Mrima hill, unless the disease causing pathogens are introduced. There is need for further studies to establish the effect of radiation on reproductive capacity and survival of disease vectors in the study area.

Keywords: Mrima, mosquitoes, sand flies, radiation, 232Thorium.