CLONAL VARIATION IN FOLIAR CHEMISTRY OF ASPEN - EFFECTS ON GYPSY MOTHS AND FOREST TENT CATERPILLARS

Quaking aspen (Populus tremuloides) exhibits striking intraspecific va riation in concentrations of phenolic glycosides, compounds that play important roles in mediating interactions with herbivorous insects. Th is research was conducted to assess the contribution of genetic variat ion to overall phenotypic variation in aspen chemistry and interaction s with gypsy moths (Lymantria dispar) and forest tent caterpillars (Ma lacosoma disstria). Thirteen aspen clones were propagated from field-c ollected root material. Insect performance assays, measuring survival, development, growth, and food utilization indices, were conducted wit h second and/or fourth instars. Leaf samples were assayed for water, n itrogen, total nonstructural carbohydrates, condensed tannins, and phe nolic glycosides. Results showed substantial among-clone Variation in the performance of both insect species. Chemical analyses revealed sig nificant among-clone variation in all foliar constituents and that var iation in allelochemical contents differed more than variation in prim ary metabolites. Regression analyses indicated that phenolic glycoside s were the dominant factor responsible for among-clone variation in in sect performance. We also found significant genetic trade-offs between growth and defense among aspen clones. Our results suggest that genet ic factors are likely responsible for much of the tremendous phenotypi c variation in secondary chemistry exhibited by aspen, and that the ge netic structure of aspen populations may play important roles in the e volution of interactions with phytophagous insects.