Abstract:
In traditional African communities, repellent volatiles from certain plants
generated by direct burning or by thermal expulsion have played an important role
in protecting households against vectors of malaria and other diseases. Previous
research on volatile constituents of plants has shown that some are good sources
of potent mosquito repellents. In this bioprospecting initiative, the essential
oil of leaves of the tree, Suregada zanzibariensis Verdc. (Angiospermae:
Euphobiaceae) was tested against the mosquito, Anopheles gambiae s.s. Giles
(Diptera: Culicidae) and found to be repellent. Gas chromatography (GC),
GC-linked mass spectrometry (GC-MS) and, where possible, GC-co-injections with
authentic compounds, led to the identification of about 34 compounds in the
essential oil. About 56% of the constituents were terpenoid ketones, mostly
methyl ketones. Phenylacetaldehyde (14.4%), artemisia ketone (10.1%),
(1S)-(-)-verbenone (12.1%) and geranyl acetone (9.4%) were the main constituents.
Apart from phenylacetaldehyde, repellent activities of the other main
constituents were higher than that of the essential oil. The blends of the main
constituents in proportions found in the essential oil were more repellent to An.
gambiae s.s. than was the parent oil (p < 0.05), and the presence of artemisia
ketone in the blend caused a significant increase in the repellency of the
resulting blend. These results suggested that blends of some terpenoid ketones
can serve as effective An. gambiae s.s. mosquito repellents.
