Bio-efficacy of Certain Indigenous Plant Extracts against Red Spider Mite, Oligonychus coffeae , Nietner (Tetranychidae: Acarina) Infesting Tea

Leaf extracts of five different locally available plants such as Polygonum hydropiper  L. , Vitex negundo L , Tithonia diversifolia (Hemsl.) (wild sun flower), Artemisia vulgaris L and Clerodendrum infortunatum L were evaluated for their ovicidal and acaricidal activity against the tea red spider mite, Oligonychus coffeae , Nietner (Tetranychidae: Acarina) in the laboratory using the leaf disc method under controlled conditions. Leaves collected from the above mentioned plants were dried under shade, milled in an electric blender and extracted using two different solvents, hexane and methanol and prepared different concentrations viz. 1%, 0.75%, 0.50% and 0.25% by diluting in DMSO (dimethyl sulfoxide; an important polar solvent) and were used for different bioassays. The effects of the extracts on the mortality of adults as well as in the eggs were assessed after spraying and the results were compared with an untreated control. All tested plants showed varying levels of efficacy on red spider mite compared when with the untreated control. Among five plant species tested, methanol extract of Vitex negundo and Clerodendrum infortunatum showed maximum ovicidal action (66.71% and 57.45% respectively) and exhibited more than 90% adult mortality @ 1% conc. of both the hexane and methanol extract of Vitex negundo and Clerodendrum infortunatum after 24 h.