A Membrane Filter Bioassay for Studying Phagostimulatory Materials in Leaf Extracts1

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Abstract
Adults of the obscure root weevil, Sciopithes obscurus Horn, were exposed in a circular arena to non-treated membrane filter discs and those treated with a leaf extract of Rhododendron thomsonii Hook. The area of disc eaten indicates phagostimulatory activity. Membrane filters composed of a combination of cellulose acetate and cellulose nitrate are superior to other substrates tested because they are biologically inert, homogeneous in consistency, and permit the even distribution of applied substances. Hexane extracts of leaves of R, thomsonii stimulate feeding and the extent of feeding is proportional to the concentration of the extract. A rapid method for measuring the consumed area of discs is also described.