Bioefficacy of Solvent Fractions of Oreosyce africana and Piper capense against the Malaria Vector, Anopheles arabiensis with High Performance Liquid Chromatographic and Ultraviolet-Visible Spectroscopic Analysis

The efficacy of synthetic inorganic insecticides to control malaria vector mosquitoes is compromised by increased mosquito resistance to insecticides. Furthermore, use of inorganic insecticides raises serious environmental toxicity concerns. The test plants, Oreosyce africana and Piper capense were identified in Ethiopia through ethnobotanical leads obtained on the basis formal and informal field interviews and discussions coupled with literature search for sister species tested elsewhere. The plant powder from these species was extracted using 80% methanol and the methanol crude extracts of Oreosyce africana and Piper capense were sequentially fractionated with solvents (dichloromethane, ethyl acetate and deionized water). Each fraction was dissolved in dimethyl sulfoxide and deionized water; test concentration prepared and tested for their bioactivity against Anopheles arabiensis adults. The dichloromethane fraction of Oreosyce africana and ethyl acetate fraction of Piper capense had higher adulticidal activities with LC50 and LC90 values of 4.27 and 14.12 ppm and 10.72 and 30.59 ppm, respectively. Comparison of dichloromethane fraction of Oreosyce africana with ethyl acetate and water fractions showed significant differences at p<0.05. And comparison of ethyl acetate fraction of Piper capense with dichloromethane and water fractions showed significant differences at p<0.05. Thus, the bioassays with dichloromethane fraction of Oreosyce africana and ethyl acetate fraction of Piper capense exhibited higher adulticidal effect against Anopheles arabiensis than other solvent fractions. Dichloromethane fraction of Oreosyce africana and ethyl acetate fraction of Piper capense were examined under HPLC and UV-Vis for the proximate analysis. These plant products would be ideal alternatives for the control of malaria vector mosquitoes upon fractionation and preparation of suitable delivery packages.