Abstract
BackgroundThe use of plant repellents against nuisance biting insects is common and its potential for malaria vector control requires evaluation in areas with different level of malaria endemicity. The essential oils of Ocimum suave and Ocimum kilimandscharicum were evaluated against malaria vectors in north-eastern Tanzania.MethodologyAn ethnobotanical study was conducted at Moshi in Kilimanjaro region north-eastern Tanzania, through interviews, to investigate the range of species of plants used as insect repellents. Also, bioassays were used to evaluate the protective potential of selected plants extracts against mosquitoes.ResultsThe plant species mostly used as repellent at night are: fresh or smoke of the leaves of O. suave and O. kilimandscharicum (Lamiaceae), Azadirachta indica (Meliaceae), Eucalyptus globules (Myrtaceae) and Lantana camara (Verbenaceae). The most popular repellents were O. kilimandscharicum (OK) and O. suave (OS) used by 67% out of 120 households interviewed. Bioassay of essential oils of the two Ocimum plants was compared with citronella and DEET to study the repellence and feeding inhibition of untreated and treated arms of volunteers. Using filter papers impregnated with Ocimum extracts, knockdown effects and mortality was investigated on malaria mosquito Anopheles arabiensis and Anopheles gambiae, including a nuisance mosquito, Culex quinquefasciatus. High biting protection (83% to 91%) and feeding inhibition (71.2% to 92.5%) was observed against three species of mosquitoes. Likewise the extracts of Ocimum plants induced KD90 of longer time in mosquitoes than citronella, a standard botanical repellent. Mortality induced by standard dosage of 30 mg/m2 on filter papers, scored after 24 hours was 47.3% for OK and 57% for OS, compared with 67.7% for citronella.ConclusionThe use of whole plants and their products as insect repellents is common among village communities of north-eastern Tanzania and the results indicate that the use of O. suave and O. kilimandscharicum as a repellent would be beneficial in reducing vector biting. The widespread use of this approach has a potential to complement other control measures.
Highlights
The use of plant repellents against nuisance biting insects is common and its potential for malaria vector control requires evaluation in areas with different level of malaria endemicity
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]
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
Summary
The use of plant repellents against nuisance biting insects is common and its potential for malaria vector control requires evaluation in areas with different level of malaria endemicity. 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 [1]. 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 biodegradable [11,12]. Compared to other synthetic compounds, natural products are presumed to be safer for human use [13], justifying a broad search for eco-friendly biological materials to be used for the control of vectors of medical importance
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