<p class="first" id="d1637222e117">Mosquito-borne diseases represent a deadly threat
for millions of people worldwide.
Eco-friendly mosquitocides are a priority. In Ayurvedic medicine, Plectranthus species
have been used to treat heart disease, convulsions, spasmodic pain and painful urination.
In this research, we evaluated the acute toxicity of essential oil from Plectranthus
barbatus and its major constituents, against larvae of the malaria vector Anopheles
subpictus, the dengue vector Aedes albopictus and the Japanese encephalitis vector
Culex tritaeniorhynchus. The chemical composition of P. barbatus essential oil was
analyzed by gas chromatography-mass spectroscopy. Nineteen components were identified.
Major constituents were eugenol (31.12%), α-pinene (19.38%) and β-caryophyllene (18.42%).
Acute toxicity against early third-instar larvae of An. subpictus, Ae. albopictus
and Cx. tritaeniorhynchus was investigated. The essential oil had a significant toxic
effect against larvae of An. subpictus, Ae. albopictus and Cx. tritaeniorhynchus,
with 50% lethal concentration (LC50) values of 84.20, 87.25 and 94.34 μg/ml and 90%
lethal concentration (LC90) values of 165.25, 170.56 and 179.58 μg/ml, respectively.
Concerning major constituents, eugenol, α-pinene and β-caryophyllene appeared to be
most effective against An. subpictus (LC50 = 25.45, 32.09 and 41.66 μg/ml, respectively),
followed by Ae. albopictus (LC50 = 28.14, 34.09 and 44.77 μg/ml, respectively) and
Cx. tritaeniorhynchus (LC50 = 30.80, 36.75 and 48.17 μg/ml, respectively). Overall,
the chance to use metabolites from P. barbatus essential oil against mosquito vectors
seems promising, since they are effective at low doses and could be an advantageous
alternative to build newer and safer mosquito control tools.
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