Abstract
The adulticidal activities of essential oils of eleven plants namely Chenopodium ambrosioides, Eucalyptus citriodora, Eucalyptus globules, Lippia adoensis, Mentha spicata, Nigella sativa, Ocimum lamiifolium, Ocimum suave, Piper nigrum, Schinus molle and Thymus vulgaris were assessed against a laboratory colony of Anopheles arabiensis in Ethiopia. The Centers for Disease Control and Prevention (CDC) glass bottle bioassay was adopted to conduct bioefficacy tests. For each replicate, ten blood-unfed female An. arabiensis were exposed to different concentrations of essential oils coated in glass bottles, and mortality was recorded at intervals of 5 minutes for one hour to assess the mean percentage mortality and LC50 and LC90 values. The residual toxicity of six essential oils was also assessed by exposing adult An. arabiensis in nylon netting Barraud cages treated by oils. Of all the essential oils assessed for adulticidal activities, O. suave was found to be toxic at low concentration (LC50 = of 0.0014 ml% v/v; LC90 = 0.0027 ml% v/v). The next efficacious oil was that of T. vulgaris with LC50 and LC90 values of 0.0028 ml% v/v and 0.005 ml% v/v, respectively. The lowest activity was due to S. molle, E. globulus and P. nigrum. At a concentration of 0.05 ml% v/v, O. suave killed 100% of An. arabiensis within five minutes of exposure, while P. nigrum at the same duration caused similar rate of mortality at a concentration of 50 fold. Residual toxicity tests revealed O. suave to persist for 15 days, killing all mosquitoes in the first five days and 80% up to 10 days. The lowest residual activity was noted for E. citriodora which persisted only for 2 days. The essential oil O. suave acquired the highest level of toxicity at low concentration and within a short time. The efficacious nature of most plants has an implication for more screening of components of these plants with potential adulticides and develops for mosquito control.
Highlights
Members of the Anopheles gambiae complex are the most important vectors of malaria in sub-Saharan Africa of which Anopheles gambiae s.s. and Anopheles arabiensis are the most widely distributed and most efficient vectors [1,2]
Of all the essential oils assessed for adulticidal activities, O. suave was found to be toxic at low concentration (LC50 = of 0.0014 ml% v/v; LC90 = 0.0027 ml% v/v)
The bioactivity results showed that the O. suave acquired the highest level of toxicity at low concentration
Summary
Members of the Anopheles gambiae complex are the most important vectors of malaria in sub-Saharan Africa of which Anopheles gambiae s.s. and Anopheles arabiensis are the most widely distributed and most efficient vectors [1,2]. Vector control by the application of insecticides remains one of the most important strategies in the prevention and control of malaria. Indoor residual spraying (IRS) of insecticides and long lasting insecticidal treated nets (LLINs) are the two important tools utilized by a number of programmes. Repeated application of insecticides is increasing the selection pressure for resistance in malaria vectors highlighting the need for new strategies for control [3] and plants products have received due attention as potential bioactive compounds against disease vectors. The chance of developing resistance to plant products seems to be low [5]. The majority of research has focused on the OPEN ACCESS
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