Constituents of the essential oil of Suregada zanzibariensis leaves are repellent to the mosquito, Anopheles gambiae s.s

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.

Figure 1.

Chemical structures of methyl ketone terpenes and main constituents of Suregada zanzibariensis essential oil. High quality figures are available online.

Figure 2.

Percentage protective efficacy (± SE) of Suregada zanzibariensis essential oil and blends of the main constituents against Anopheles gambiae s.s. Ratios of weight of the main constituents used in preparation of blends are 14:12:10:9 for phenylacetaldehyde (5): verbenone (17): artemisia ketone (11): geranyl acetone (24); Columns with the same letters at a given concentration are not significantly different at P < 0.05 (Student-Newman-Keuls test). High quality figures are available online.