Abstract
BackgroundThe emergence and spread of resistant strains of malaria vectors to chemical insecticides are becoming major problems for malaria vector management. Natural plant products have a vital role to play in the current challenge of malaria control. The current study was conducted to evaluate insecticidal effect of ethnobotanical plant extracts against the primary malaria vector, Anopheles arabiensis in northwestern Ethiopia.MethodsPrimarily, ethnobotanical plants used for Anopheles mosquito control were surveyed in Dangur district, northwestern Ethiopia. Insecticide-susceptible strains of Anopheles arabiensis mosquito were reared in the insectary of the Tropical and Infectious Diseases Research Centre, Assosa University. After surveying plants used for mosquito control in local people, four frequently used plants were identified for extraction. The larvicidal and adulticidal potential of frequently used plant extracts against susceptible strains of the laboratory colony were evaluated.ResultsA total of 15 plants were identified as ethnobotanical plants that help local people with mosquito control. Azadirachta indica, Ocimum lamiifolium, Ocimum americanum, Moringa olifeira leaf, and Moringa olifeira seed species of local plants were found to be frequently used to kill and/or repel mosquitoes in the study district. All the plant extracts were found to have potential larvicidal activity against fourth instar larvae of An. arabiensis and only ethanol and methanol extract of Azadirachta indica and Ocimum lamiifolium were found to have potential adulticidal effect against adult of An. arabiensis. The highest larvicidal activity was observed in ethanol extract of Azadirachta indica with 95% larval mortality and lowest Lethal Concentration 50 (LC 50) of 40.73parts per million (ppm) and LC90 of 186.66 ppm. The highest adulticidal activity was observed in methanol extract of Azadirachta indica with 75% adult mortality at 300 ppm and lowest LC50 of 106.65 ppm and LC90 of 1,293 ppm. The lowest larvicidal and adulticidal activity was observed in methanol extracts of Ocimum lamiifolium with 63.35% larval mortality and leaf extract of Moringa olifeira with 50% adult mortality at 300 ppm, respectively.ConclusionEthanol extract of Azadirachta indica exerted a remarkable larvicidal effect against An. arabiensis and thus it can be used for botanical mosquito insecticide development. Since the current finding is based on susceptible strain of An. arabiensis, further work on wild mosquitoes is recommended.
Highlights
The emergence and spread of resistant strains of malaria vectors to chemical insecticides are becoming major problems for malaria vector management
From all plant species collected and identified, the most frequently used plants (Azadirachta indica (75%), Ocimum lamiifolium (65%), Ocimum americanum (70%), leaf of Moringa olifeira (50%), and seeds of Moringa olifeira (50%)) were selected to test their larvicidal and adulticidal effects against An. arabiensis
Out of all local plant species used for mosquito control the most frequently used were Azadirachta indica (75%), Ocimium lamiifolium (65%), Ocimium americanum (70%), leaf of Moringa olifeira (50%), and seeds of Moringa olifeira (50%)
Summary
The emergence and spread of resistant strains of malaria vectors to chemical insecticides are becoming major problems for malaria vector management. The current study was conducted to evaluate insecticidal effect of ethnobotanical plant extracts against the primary malaria vector, Anopheles arabiensis in northwestern Ethiopia. The wide spread of insecticide-resistant strains of Anopheles is challenging chemical insecticide-based malaria control strategies. Insecticide susceptibility tests carried out in Ethiopia have shown different levels of resistance by the principal vector to insecticides in use for IRS and/or to treat LLINs [4, 5]. For these reasons, looking for an alternative is becoming of major interest to scientists and policymakers working in the area
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