Abstract
This paper report on assessment of the chemicals derived from Tanzanian botanical resource as a viable source of safe, environmentally friendly and low cost mosquitocidal agents, but has yet to be developed into simple blends and formulations to be used in malaria control campaigns. Selection of bioactive plant species were based on random screening, phytochemical targeting, ethnobotanical survey, chemotaxonomic approach and targeted screening approach. The crude extracts from leaves, stem and root barks, and pure isolated compounds from over 20 different Tanzania plant species have been established to possess antimosquito activities. The bioassay experiments were based on cytotoxicity screening in BST followed by mosquitocidal assays of larvicidal, tarsal contact and repellency bioassays. The activities were characterized to be larvicidal, growth disruptors, insecticidal and repellents. Seasonal variations, geographical locations, isolation of small amounts of pure compounds, limits in the availability of essential facilities such as NMR spectroscopy, MS and X-ray diffraction analysis for structural elucidation, stereochemical and conformational assignments, have been realised to be among the impediments in the search and establishment of new and biodegradable botanical natural products. The results suggest that the investigated plant species are promising as mosquitocidal agents and could be useful leads for the development of new insecticide products. @JASEM
Highlights
Charles KihampaMosquito bioassay by tarsal contact with deposits on filter paper: The tests conducted by applying a series of dosages by dipping the filter paper (Whatman No 1) in 50 ml solutions of the sample dissolved in alcohol
Over the past 20 years or so several researchers have embarked on the search for insecticides that would be useful in the control of malaria transmitting mosquitoes and other insect pests
Selection and collection of the plant materials: In the selection of plant species for pharmacological and insecticidal screening, five approaches have been considered to be effective. These include random screening which involves collection of all plant species from a particular study area, phytochemical targeting that aimed at the collection of all members of the plants family known to be rich in bioactive compounds, ethnobotanical survey that is based on traditional uses of the plant(s), chemotaxonomic approach that is based on plants having similar constituents which may be in different families, and targeted screening of specific parts of a plant such as the seeds, barks, roots, leaves and other parts
Summary
Mosquito bioassay by tarsal contact with deposits on filter paper: The tests conducted by applying a series of dosages by dipping the filter paper (Whatman No 1) in 50 ml solutions of the sample dissolved in alcohol. After the bioassay of each concentration, the arms were washed with bar soap, rinsed well with tap water and allowed to dry for 15-20 min, before application of the dose of the test sample. Where PCM is the percent control mean and PTM is the percent test mean of mosquitoes landing on the control and treated arms respectively. From the late 1990s to the present several Tanzanian plant species have been investigated by various researchers for their antimosquito properties These include, Neorautanenia mitis, known as Lidupala by Hehe tribe in Iringa region, where it is used as an insecticide for insect infestation in maize. Phytochemical investigations of the dichloromethane and ethanol extracts of the cytotoxic root barks of Hugonia castaneifolia and H. busseana (Linaceae) yielded the rosane diterpenoids hugorosenone and 18hydroxyhugorosenone, and tetracosyl-(E)-ferrulate and a sesquiterpenoid 4-methoxy-5,9-oxahimachal-9ene, respectively that exhibited mosquito larvicidal activity against An. gambiae after 24 and 48 h exposure (Baraza et al 2007; Baraza et al, 2008)
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