Evaluation of Essential Oils of Some Local Plants for their Repellency against Anopheles arabiensis and Aedes aegypti
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Date
2006-07
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Addis Ababa University
Abstract
Essential oils of six aromatic plants: Ocimum suave, O. lamiifolium, Eucalyptus citriodora, E. globulus, Lippia adoensis and Schinus molle were evaluated for their repellent activity against Anopheles arabiensis and Aedes aegypti. The experiments were conducted in the laboratory established at Aklilu Lemma Institute of Pathobiology using human volunteers. Each volunteer used his left arm for control and right arm for treatment and area from wrist to fingers was covered by surgical glove. First, the control arm was exposed to 30 nuliparous mosquitoes starved for 3-6 days inside a screened cage and the landing/biting mosquitoes were counted in 30 seconds. And immediately thereafter, the treated arm was exposed in the cage for the same 30 seconds and the landing/biting mosquitoes were counted and percentage of protection was computed.
At 20% concentration, percentages of protections of the test oils were compared with the standard synthetic DEET. In case of An. arabiensis, DEET provided 83-100% protection for 6 hours, O. suave 83-100% for 4 hours, L. adoensis 89-100% for 2 hours, and E. citriodora, E. globulus, S. molle, but O. lamiifolium did not provide any protection even for an hour. In case of Ae. aegypti, DEET provided 84-100% protection for 6 hours, O. suave 85-100% for 5 hours, L. adoensis for an hour, and the rest four oils did not provide protection even for an hour. At 10% concentration all the test oils did not provide protection for an hour against both An. arabiensis and Ae. aegypti except O. suave which provided 88-100% protection for 3 hours against Ae. aegypti. In the study of repellency of blend effects of the six oils against An. arabiensis, O. suave + L. adoensis, O. suave + E. citriodora, O. suave + E. globulus, O. suave + S. molle and O. suave + O. lamiifolium provided over 84% protection for 3 hours, and the other blends without O. suave provided protection for less than and nearly an hour at 20% concentration, and blend effects of the five oils with O. suave provided protection for an hour, where as the other blends other than O. suave provided less than an hour protection at 10% concentration.
All six essential oils and blends exhibited repellent properties in various degrees to adult female mosquitoes of An. arabiensis and Ae. aegypti. But, of the six oils L. adoensis against An. arabiensis, O. suave against An. arabiensis and Ae. aegypti and 1:1 combinations of O. suave with five oils against An arabiensis showed remarkable repellency. However, field investigation is required to ascertain the relative potential of repellency of L. adoensis, O. suave and mixtures of O. suave and the other oils against An. arabiensis, Ae. aegypti and other vector mosquitoes.
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Biology