Bioactivity of fractionated indigenous medicinal plant extracts of Phlomis damascena Born. and Ranunculus myosuroides against the cotton whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae)

摘要

Two bioactive methanol (MeOH) extracts of two indigenous medicinal plant species Phlomis damascena Born. and Ranunculus myosuroides Boiss. & Kotschy were tested for insecticidal activity of their fractions against the cotton whitefly Bemisia tabaci (Gennadius) adults under controlled conditions. This study is within bio-prospection context, in form of utilizing local plant species as an alternative in sustainable agriculture development. Organic solvent extraction of the two bioactive crude extracts yielded four fractions each: ethyl acetate fraction, chloroform (CHCl3) – water fraction, CHCl3-methanol (MeOH) fraction of the acid basic layer and MeOH fraction of the aqueous basic layer. The two extracts and their CHCl3-MeOH fractions caused significant decrease in number of live adult whiteflies compared to the control. Fractions of the bioactive CHCl3-MeOH of P. damascena were collected and isolated by combinations of repeated chromatography including silica gel chromatography and Thin Layer Chromatography (TLC). The most bioactive fraction was further purified using silica gel column eluted with a gradient of CHCl3: MeOH (9:1) with increasing volume of methanol till total elution; the 5 eluted sub-fractions were analyzed by TLC. The 4th isolated sub-fraction having Rf of 0.41 was eluted with CHCl3-MeOH (9:2) and was found not significantly different in its effect from the bioactive CHCl3-MeOH fraction. This is the first report for the effect on survival of insects for fractions of these two medicinal plant species in comparison to their raw extracts. Thus, the crude extracts and their chemical fractions contribute to the development of insecticidal products based on these plant species and their bioactive chemical components.