Albert Kimutai, Moses Ngeiywa, Peter G. N. Njagi, Margaret Mulaa, Johnstone Ingonga, Lydia B. Nyamwamu, Cyprian Ombati, Philip Ngumbi
The efficacy of the essential oils of Cymbopogon citratus and Tagetes minuta in causing mortality in adults of the sandfly Phlebotomus duboscqi was tested in a laboratory bioassay. The effect of the oils on oviposition by female sand flies was also evaluated. Each essential oil (EO) extract was tested at graded concentrations of 0.125; 0.250; 0.500; 0.750 and 1mg/ml in Tween 80 and a positive control of dimethyl-3-methylbenzamide (DEET). The oil and control preparations were applied onto the inner surface and bottom of a sterile pot and thirty adult sandflies P. duboscqi aspirated into the pot. The mortality of insects was recorded as the number of dead flies after 24, 48 and 72 h. In addition, the numbers of eggs oviposited by female flies that were subjected to the different treatments were recorded. The results showed that both the essential oils of T. minuta and C. citratus were highly potent against adult sand flies, P. duboscqi with mortality levels of 100.00 and 82.22 % on female sandflies and 100.00 and 88.89 % on male sandflies, respectively after 72h. Comparing the mortality levels caused by the two oils, which of C. citratus was significantly higher (P < 0.05) than the oil of T. minuta on male and female sandflies. However, at the shorter periods there was no statistical difference in mortality levels of males and females subjected to each of the two oils. With regard to oviposition, female sandflies treated with the oil of C. citratus oil laid significantly lower number of eggs than those laid by sand flies treated with T. minuta oil. Furthermore, gas chromatography-mass spectrometric analysis done on samples of the two oils showed a wide range of candidate compounds, including terpenes. In conclusion, the two essential oils are promising natural insecticides due to their safety advantage over chemical insecticides. It remains to carry out further studies in the field using human subjects before their adoption for use against Phlebotomine sandflies. In addition bioassays with individual and combinations of the constituent compounds of the essential oils may determine the candidate biologically active compounds.
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