Plant-based insect repellents: searching for inexpensive and accessible alternatives to synthetic repellents in Lao PDR Växtbaserade insektsmedel - på jakt efter billiga och lättillgängliga alternativ till syntetiska preparat Blood-feeding parasites such as mosquitoes, leeches, ticks, mites, lice, bedbugs, and myiasis-producing fly larvae are a common cause of health problems in Lao People's Democratic Republic. Several infectious diseases are spread by insect hosts, e.g. malaria, dengue fever, and Japanese encephalitis, and these are very common in rural areas in Lao People's Democratic Republic. Some of these diseases can be treated with modern pharmaceuticals, but some of the best treatments are very expensive and hard to-come-by in Lao People's Democratic Republic. Another factor complicating diseases treatment is the emergence of drug-resistance, most recently resistance of Plasmodium falciparum to the last effective cure, artemisine, has been found. Controlling the spread of these insect-disease-hosts, i.e. disease-vectors, is an important focal area in absence of effective, available or affordable treatments to these infections. Effective vector control methods include the use of pesticides, insecticide-treated bed nets, and synthetic and plant-based repellents. However, insecticide resistance, outdoor transmission, and mosquito behavioural changes threaten the effectiveness of vector control measures. The cost of synthetic chemicals for impregnation can be an important factor limiting their optimal use. Mosquito control programs often distribute bed nets and chemicals for impregnation free of charge, but sometimes it is required that people subsequently pay for future impregnation of the nets. In rural Lao areas where a majority of the population lives below the World Bank poverty line, costs of USD 4 per net and USD 1 per impregnation are unaffordable. The value of plants traditionally used to repel blood-feeding arthropods has often been underestimated. Plants used to obtain extracts or oils containing natural repellents can often be easily cultivated at a low cost in most tropical areas; especially practical are herbaceous or shrub-like species. However, research on phytochemical composition and repellence efficacy has to an extent focused only a handful of species with promising efficacy in trials, but planting lemon eucalyptus or neem trees does not provide a short-term solution for affected populations. A nationwide study of traditional knowledge on plants that are used to repel or kill hematophagous arthropods conducted by our group in 2009 identified a total of 92 plant species as traditional repellents used to repel or kill mosquitoes, bedbugs, human lice, mites and ticks, fly larvae, and blood-sucking leeches (de Boer et al., 2010). Studies on the repellence efficacy of the 9 most commonly reported species showed that the traditional plant repellents were effective repellents against leeches, fly larvae infesting foods and mosquitoes. Many of the plant-based repellents had similar efficacy to synthetic repellents. The project aims to build on quantitative ethnobiological data on plant-based repellents gathered in prior studies, and to characterize the active phytochemical constituents or/and fractions containing repellents in species that showed promising efficacy in repellence field trials; to evaluate genotype constituent variability to select plant lines with the highest levels of active compounds; and to develop protocols for local harvesting, extraction and storage of plant-based repellents in order to empower communities to create their own repellents, independent of ethnicity, location or government programs. Parasites such as leeches, mosquitoes, and myiasis-producing fly larvae are common in Lao People's Democratic Republic, and spread several endemic arthropod-borne infections, e.g., malaria, dengue fever, and Japanese encephalitis. Effective vector control methods including the use of pesticides, insecticide-treated bed nets, and synthetic and plant-based repellents are important means of control against such invertebrates. However, insecticide resistance, outdoor transmission, and mosquito behavioral changes threaten the effectiveness of vector control measures. Research by our group in 66 villages identified a total of 92 plant species as traditional repellents. Subsequent studies on the repellence efficacy of essential oil or crude extracts of the most commonly reported species showed that the traditional plant repellents were effective repellents against leeches, fly larvae and mosquitoes. Many of the plant-based repellents had similar efficacy to synthetic repellents, have promise as alternatives to expensive synthetics. This project aims to use gas chromatography (GC), high pressure liquid chromatography (HPLC) and mass spectroscopy (MS) to identify the active components in the most promising species in order to develop plant-based repellents; to evaluate genotype constituent variability; to test the efficacy of these purified or fractionated repellents using field trials; and to create easy-to-understand, intuitive protocol for local harvesting, extraction and use of the plant-based repellents.