Recently, the environmental friendly and biodegradable natural insecticides of plants origin have been receiving attention as an alternative green measure of control of arthropods of public health importance . More than two billion people, mostly in tropical countries, are at risk from mosquito-borne diseases, such as malaria, dengue, haemorrhagic fever and filariasis . Malaria accounts for 310 – 515 million clinical episodes with 1.5 – 3.0 million deaths per year, 90% of which occur in sub-Saharan Africa . The burden of malaria has been increasing due to development of resistance against both anti-malaria drugs and insecticides, complex social structures, and rapid environmental changes that have intensified in the last decade [1, 3]. Consequently, there is no single method of malaria control that is completely effective in high transmission areas [4–6]. Even the most widely tested interventions, using bed nets treated with pyrethroid insecticides, have proven difficult to implement correctly because of problems related to equity, accessibility, user compliance and insecticide resistance [7, 8]. For example, in western Kenya, the most important reasons for non-adherence to use of ITNs was the disruption of sleeping patterns due to visitors, funerals, house constructions and other events . Other concerns included fear of the insecticide, which is thought by some, to be a toxic drug used for family planning purposes . Insect repellents play an important role in reducing man-vector contact . Repellents of plant origin have been used for medicinal purposes for a long time because they do not pose hazards of toxicity to human or domestic animals and are easily biodegradable [11, 12]. Compared to other synthetic compounds, natural products are presumed to be safer for human use , justifying therefore a broad search for eco-friendly biological materials to be used for the control of vectors of medical importance.
The chemical contents extracted from plant materials can be useful as repellents, larvicides, oviposition attractants, insect growth hormone regulators and deterrent agents [11, 14, 15]. Plant products have been used in many parts of the world for killing or repelling mosquitoes either as extracts or as whole plant . Certain natural products have been investigated for repellent activity against mosquitoes [17, 18]. Ocimum kilimandscharicum (OK) and Ocimum suave (OS) have been reported to possess repellent properties against mosquitoes . The repellent action of plant parts or oil extracts from Ocimum species have been evaluated against Afro-tropical mosquitoes [16, 19]. Quelling, an insect repellent produced in Asia, derived from extracts of the eucalyptus and lemon grass has been evaluated against mosquitoes . Essential oil obtained from Vitex negudo and flowers from Lantana camara have shown repellence activities against Aedes aegypti [20, 21].
This study present an account of plants used as insect repellents in north-eastern Tanzania and evaluates the feeding inhibition, knockdown effect and mortality effect of two common repellents, Ocimum suave and Ocimum kilimandscharicum plants against An. gambiae ss, An. arabiensis and Cx. quinquefasciatus.