1.1 Background to the study
Plant essential oils (EOs) have been widely used for many years due to their antimicrobial properties in foods and pharmaceutical products 1. Essential oils are natural products obtained from plants. It is estimated that the global number of plants is of the order of 300,000 and about 10% of these contains essential oils and could be used as a source for their production 2. A large number of essential oils extracted from different families have been shown to have high repellence against arthropod species. Among the essential oil producing plants, such as Cymbopogon spp., Eucalyptus spp. and Ocimum spp. have been widely studied. Cymbopogon plants have been traditionally used to repel mosquitoes in jungle regions such as the Bolivian Amazon 3. Cymbopogon produces the most used natural repellents in the world 4. Many extracts and essential oils isolated from these plants have been tested against different kinds of arthropods. Cymbopogon excavatus gave 100% repellence for 2 h, when it was evaluated in the laboratory against Anopheles arabiensis and its repellence decreased to 59.3% after 4 h 5.
Mosquito-borne diseases cause significant morbidity, mortality and economic burden to humankind 6. The mosquito, Aedes aegypti is the major vector of yellow fever, dengue and dengue hemorrhagic fever (DHF). These mosquito-borne infections are found in tropical and sub-tropical regions around the world, predominantly in urban areas and semi-urban areas. The global incidence of dengue has grown dramatically around the world in recent decades and there are approximately 2.5 billion people at risk 7. One of the methods available for the control of mosquitoes is the use of insecticides. In last two decades, the use of chemical insecticides in mosquito control method has resulted in instability of the environment, mosquito resistance, mosquito resurgences and toxic to nontarget organisms including natural enemies in the agriculture ecosystem 8. Hence, it has now become important to find an alternative means of mosquito control method, which can eliminate the use of chemical pesticides 9.