Abstract:
BACKGROUND & OBJECTIVES: Lantana viburnoides sp viburnoides var kisi is used in
Tanzania ethnobotanically to repel mosquitoes as well as in traditional medicine
for stomach ache relief. Bioassay-guided fractionation and subtraction bioassays
of the dichloromethane extract of the root barks were carried out in order to
identify the bioactive components for controlling Anopheles gambiae s.s. mosquito
larvae.
METHODS: Twenty late III or early IV instar larvae of An. gambiae s.s. were
exposed to various concentrations of the plant extracts, fractions, blends and
pure compounds, and were assayed in the laboratory by using the protocol of WHO
1996. Mean mortalities were compared using Dunnett's test (p < 0.05) and lethal
concentration calculated by Lackfit Inversel of the SAS programme.
RESULTS: The crude extract (LC50 = 7.70 ppm in 72 h) and fractions exhibited
different level of mosquito larvicidal activity with subtraction of some
fractions resulting in activity enhancement. The active fractions contained
furanonaphthaquinones regio-isomers (LC50 = 5.48-5.70 ppm in 72 h) and the
lantadene triterpenoid camaric acid (LC50 = 6.19 ppm in 72 h) as active
principles while the lupane triterpenoid betulinic acid (LC50 < 10 ppm in 72 h)
was obtained from the least active fraction.
INTERPRETATION & CONCLUSION: Crude extracts and some fractions had higher or
comparable larvicidal activity to the pure compounds. These results demonstrate
that L. viburnoides sp viburnoides var kisi extracts may serve as larvicides for
managing various mosquito habitats even in their semi-purified form. The isolated
compounds can be used as distinct markers in the active extracts or plant
materials belonging to the genus Lantana.
