Investigation of the Bases of Resistance of Selected Rhododendron Species to Foliar Feeding by the Obscure Root Weevil ( Sciopithes obscurus ) 1

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Abstract
The bases of resistance of 10 Rhododendron species listed as resistant to foliar feeding by obscure root weevils ( Sciopithes obscurus Horn) have been investigated. Feeding on 3 of the 6 Iepidote (scaled) species was significantly less than on ‘Cynthia’, a susceptible cultivar, in tests with both intact leaves and leaf discs. Only one of the 4 elepidote species, R. williamsianum , was fed on significantly less than Cynthia in both kinds of tests. A potent hexanes soluble feeding inhibitor was detected by use of a membrane filter bioassay technique in extracts from 5 of the lepidote species. Evidence of chemical feeding inhibitors in extracts from the elepidote species was less clear cut. Removal of the curled edge from leaves of R. williamsianum decreased their resistance to weevil feeding.