Consequences of clonal variation in aspen phytochemistry for late season folivores

This research was conducted to assess variation in the phytochemistry of as pen (Populus tremuloides Michaux) clones and its impact on two summer-feedi ng insect species: Canadian tiger swallowtails (Papilio canadensis Rothschi ld & Jordan) and big poplar sphinx moths (Pachysphinx modesta Harris). Eigh t aspen clones were established from root cuttings collected in the field a nd grown for two years in a common garden. Leaf tissues were assayed for wa ter, nitrogen, total nonstructural carbohydrates, condensed tannins, and ph enolic glycosides. Both long- and shea-term feeding trials were conducted t o evaluate the effects of foliage quality on insect performance. Chemical a nalyses showed that concentrations of phytochemicals varied significantly a mong aspen clones, and that such variation was greater for secondary metabo lites than for primary metabolites. Performance of both insect species vari ed among aspen clones and was negatively correlated with foliar phenolic gl ycoside concentrations. Comparison of results from this and an earlier stud y with the same plants indicates that genetic factors influence both clonal variation in secondary chemistry and phenological expression of such varia tion through time.