A methodology for developing plant-based mosquito biocides

In the South American and Southeast Asian forests, the Anopheles mosquito malaria vectors bite outdoors early in the evening, and rest outdoors. These behaviours preclude complete control by insecticides and bednets. Personal protection is necessary to protect from drug-resistant malaria. The thesis investigates the development of novel, plant-based mosquito control and personal protection: 1) discovery of new, culturally acceptable plants, 2) laboratory testing of those plants and 3) field testing of efficacious candidates as revealed by laboratory testing. Focus is upon on development of robust methodologies for the laboratory and field that carefully consider Anopheles behaviour to minimise bias. In Phase 1, an ethnobotanical survey in Yunnan, China, investigating knowledge, attitudes and practise about malaria and personal protection, several potentially insecticidal plants traditionally used against insects were identified. Knowledge of malaria was low, but everyone used personal protection at home, but not outdoors, to prevent nuisance biting. The expense of personal protection precluded use and the incorporation of plants into a low-cost insect repellent or mosquito coil would be acceptable for Yunnan. In Phase 2, a laboratory evaluation of neem (Azadirachta indica) as a larvicide, oviposition kairomone and bednet treatment, several assay methods were compared. WHO methodologies proved robust, and should be used as gold standards. When testing oviposition kairomones, choice tests should be run parallel with no-choice tests, as Anopheles mosquitoes oviposit in sub-optimal substrates in the absence of choice. A novel laboratory assay representing a normal exposure of bednet treatment to host-seeking mosquitoes was developed. In Phase 3, a field evaluation of plant based repellents in Bolivia, focus groups and novel repellents were investigated. Volatilisation of repellents proved unsuitable for use in open housing. 20%, of mosquitoes, are diverted from deet repellent-protected to unprotected individuals. The implications for repellent-testing methodology, and repellents as a means of disease control, are discussed.