Essential oils were extracted from the leaves of Hyptis suaveolens by hydro-distillation, Mosquitocidal effect was done through an experiment devised for the purpose of this research. 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 Hyptissuaveolens may have contributed to its insecticidal and mosquitocidal repellency properties.
1.1Background to the study
Plants have always served as food and medicine to man since the beginning of life. Their nutritional and medicinal potentials have been attributed to the phytochemicals and other chemical constituents contained in them. Despite their importance, it has been reported that out of the 250,000 to 500,000 species of existing plants on earth, only about 300 species are utilized in the food, pharmaceutical, cosmetics and perfume industries. Traditionally used medicinal plants produce a variety of compounds of known therapeutic properties (Umedum et al., 2014).
Medicinal plants are used in traditional treatments to cure variety of diseases. In the last few decades there has been an exponential growth in the field of herbal medicine. Natural products have been a source of drugs for centuries (Dinet al., 2011). Traditional medicines (plants source) has been used for thousands of years for the treatment of malaria and are the source of two main groups (artemisinin and quinine derivatives) of modern antimalarial drugs (Kazembe et al., 2012).
Repellents are substances applied to the skin, which prevent insects from biting such surface (Traoré-Coulibalyet al., 2013).An insect repellent is a substance that causes an organism to move away from the odour source, insects perceive the volatile repellents by smell (Luts etal., 2014).
Essential oils are volatile natural complex secondary metabolites characterized by a strong odour and have a generally lower density than that of water (Arun et al., 2009).