CHARACTERIZATION, INSECTICIDAL AND MOSQUITO REPELLENCY PROPERTIES OF ESSENTIAL OILS FROM HYPTIS SUAVEOLENS LEAVES

Thesis Abstract

The effect of the essential oils against mosquito larvae (larvicidal), mosquito repellency effect and physicochemical properties were determined using standard methods. Gas Chromatography-Mass Spectrometry (GCMS) and Fourier Transform Infra-Red (FTIR) were both done on the essential oils. Percentage yield of the essential oils was gotten as 0.05, for the larvicidal activity dose dependent mortality of the larvae was observed; there was low mortality rate at lower dosage and not significantly different from each other e.g. 6.25 and 12.50ppm had same LC50 and LC90 of 25.21 and 302.67 respectively, 25ppm had LC50 and LC90 of 9.58 and 352.46 respectively, while 50-1000ppm had LC50 and LC90 of 0.55 and 0.85 respectively. It was observed that the amount of air that enters and leaves the cage affect the rate at which mosquitoes were repelled. In a group of mosquitoes kept in a cage with all sides open (ASO) 65% of the mosquitoes were repelled within 30 minutes while for one side open (OSO) and all sides closed (ASC), 73% and 85% of the mosquitoes were repelled within the same time frame. In a second experiment, 100% of mosquitoes were repelled from the surface of rats with shaven skin where essential oil was applied. The essential oil also demonstrated dose dependent mosquitocidal activity with LC50 and LC90 values of 6 and 21ppm respectively. The essential oil has the following physicochemical properties; Iodine value 23.59+0.12g/100g, saponification 100.18+0.8mgKOH/g, Peroxide value 40.00+0.02meq/kg, Acid value 3.37+0.01mgKOH/g, Ester value 34.30+1.00mg/g and free fatty acids 0.15+0.57%. GC-MS analysis revealed Terpenes to be the major organic compound present in the essential oil which was confirmed by FTIR with the O=C-O-C stretch functional group indicating the presence of terpenes. Thus, the presences of terpenes in Essential oil of Hyptis suaveolens may have contributed to its insecticidal and mosquitocidal repellency properties.