Laboratory Investigation of the Repellency of Essential Oils of Some Local Plants against Anopheles Arabiensis and Aedes Aegypti in Ethiopia
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Date
2007-07
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Addis Ababa University
Abstract
Essential oils extracted by hydro-distillation from six plant species growing in Ethiopia,
Chenopodium ambrosioides (Chenopodiaceae), Laggera tomentasa (Asteraceae),
Eucalyptus camaldulensis (Myrtaceae), Cymbopogon citratus (Poaceae),Citrus sinensis
(Rutaceae) and Ruta chalepensis (Rutaceae), were evaluated for repellency on forearms
of human volunteers against Anopheles arabiensis and Aedes aegypti under laboratory
condition (at 10% and 20% concentration). At 10% concentration oils of L. tomentosa, E.
camaldulensis and Cy. citratus protected An. arabiensis for up two hours with mean
protection of 80.87% - 93.45%. Chenopodium ambrosioides produced 69.6% protection
at the first hour. Two other plants (R. chalepensis and Ci. sinensis) were only highly
effective for 1 hour. With increased concentrations (20%), L. tomentosa, E.
camaldulensis and Cy. citratus gave the highest repellency (80.3% - 91%) and the longest
duration of protection lasting for three hours against An. arabiensis. The repellency of Ci.
sinensis and R. chalepensis only improved slightly from the 10% concentration.
Chenopodium ambrosioides did not provide significant protection even for one hour at
20% concentration against An. arabiensis. At 10 % concentration, only one plant oil (Cy.
citratus) gave about 91% protection lasting for one hour against Ae. aegypti. The
remaining oils gave very weak protection starting even after the first hour of application
against Ae. aegypti. At higher concentration (20%), five more plants except Ch.
ambrosioides continued to give high protection (81% - 93. 4%) for only one hour of post
application against Ae. aegypti. It was also observed that Ae. aegypti was more tolerant to
all the candidate repellent plants than An. arabiensis at both concentrations. The
experiment also were evaluated the 1:1 combination of essential oils against An.
arabiensis and Ae. aegypti. Almost all blends failed to produce significant protection
beginning from the first hour. At 20% concentration there was only a slight improvement
at the first hour of the experiments. As for An. arabiensis, the combination of oils did not
improve their potency as repellents against Ae. aegypti even at higher concentration of
20%. DEET, the standard commercial repellent gave much longer repellency (83- 100%)
for as long as six hours of the test period against An. arabiensis. DEET continued to give
> 90 % protection for about six hours against Ae. aegypti.
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Biology