CHEMICAL CHARACTERISTICS OF CHRYSANTHEMUM CAUSE RESISTANCE TO FRANKLINIELLA-OCCIDENTALIS (THYSANOPTERA, THRIPIDAE)

Western Bower thrips, Frankliniella occidentalis (Pergande), performance on intact chrysanthemums, Dendranthema grandiflora Tzvelev was con;pared with that on the sap of squeezed chrysanthemums to examine the importance of plant chemical characteristics. Seventy-six percent of the variation in resistance of intact chrysanthemum cultivars could be explained by the variation in resistance of leaf sap. Thus, the chemical composition of chrysanthemum leaves was a significant factor in resistance to F occidentalis. Because similarities in resistance were found between flower sap, leaf sap, and intact, nonflowering chrysanthemums, we suggest there is a chemical resemblance among flowers and leaves causing thrips resistance in chrysanthemum. Crafts were made between a resistant and susceptible cultivar (cultivars 2 and 15, respectively). A resistance factor was transported from the resistant scion to the susceptible stock, further indicating that chemical compounds play a major role in chrysanthemum resistance to thrips. Relative growth and survival of F occidentalis larvae was correlated with larval longevity and the resulting feeding damage on intact chrysanthemum cultivars. Thus, growth and survival during the Ist few days can-be used as a quick measure of thrips resistance in chrysanthemum.