Bioefficacy of Selected Indigenous Plant Products against the Malaria Vector Mosquito, Anopheles arabiensis (Diptera: Culicidea) in Ethiopia

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Addis Ababa University


The efficacy of synthetic organic insecticides to control malaria vector mosquitoes is compromised by increased mosquito resistance to insecticides. Furthermore, use of inorganic insecticides raises environmental toxicity concerns. Therefore, plant-based biodegradable insecticides would be ideal alternatives for the control of malaria vector mosquitoes. This study was conducted to evauate the mosquitocidal bioefficacy of extracts from indigenous plants used in traditional medicine in Ethiopia. The test plants were identified through literature search followed by ethnobotanical surveys based on formal and informal field interviews and discussions with local practitioners. The 80% methanol crude extracts of the plant parts were tested against An. arabiensis mosquito larvae and adults. The effects were determined as LC50 and LC90 values based on probit analysis. The larvicidal effects of Aloe pirottae and Acokanthera scbimperi extracts expressed as LC50 and LC90 were 76.34 and 282.76 ppm and 133.39 and 407.93 ppm, respectively. Similarly, 80% methanol extracts of Aloe pirottae gel, Brassica nigra seed, Oreosyce africana leaf and Piper capense fruit tested on Anopheles arabiensis adults in the laboratory showed significant mortality for O. africana (LC50 at 14.88 and LC90 at 44.55 ppm) followed by P. capense (LC50 at 25.69 and LC90 at 46.32 ppm). The qualitative phytochemical analysis of O. africana and P. capense crude extracts revealed the presence of alkaloids, phenols, flavonoids, saponins, glycosides, and chromophorcs that are known to possess bioactive characteristics. The dichloromethane fraction of O. africana and ethyl acetate fraction of P. capense had higher adulticidal activities with LC50 values of 4.27 and 10.72 ppm, respectively and were significantly different (P<0.05). The chemical composition of the active purified fractions of O. africana were analysed by a combination of TLC, HPLC, NMR and GC-MS methods. Upon purification, the O. africana fractions had the most potent adulticidally activecomponents among the fractions tested. These included the fractions designated as B2'0 ( LC50 of 2.21 and LC90 of 7.81 ppm) and B2"0 (LC50 of 2.62 and LC90 of 11.78 ppm) at 24 hr postexposure and concentrations were significantly different (P<0.05). Mosquitocidal potency of the impregnated nets lasted for two months. The structural elucidation of the active ingredients in the B2'0 fraction was determined using a combination of !H- 13C-NMR, DEPT-135 and GC-MS measurements. This revealed the presence of linoleic acid (9, 12-Octadecadienoic acid (Z,Z)- (280 m/z) as the major chemical constituent (98.35%) and similar analysis of B2"0 fraction showed the presence of dibutyl phthalate (278 m/z) as the major chemical constituent (97.75%). Both compounds have proven insecticidal effects. This study has shown a high potential of O. africana leaf extract as an adult mosquito control agent that could be developed into an indigenous malaria control alternative to the expensive and increasingly less effective insecticides in use. The larvicidal potentials of A schimperi and A. pirottae that became implicit in this study need further investigation to determine their levels of potency. Key words: Acokanthera schimperi, Aloe pirottae, Oreosyce africana, Piper capense , Anopheles arabiensis, malaria, crude extracts, fractions, larvicidal activity, adulticidal activity, phytochemicals, Ethiopia



Acokanthera schimperi, Aloe pirottae, Oreosyce africana, Piper capense, Anopheles arabiensis, arabiensis, malaria, crude extracts, fractions, larvicidal activity, adulticidal adulticidal, phytochemicals;Ethiopia