Consequences of clonal variation in aspen phytochemistry for late season folivores
This research was conducted to assess variation in the phytochemistry of aspen (Populus tremuloides Michaux) clones and its impact on two summer-feeding insect species: Canadian tiger swallowtails (Papilio canadensis Rothschild & Jordan) and big poplar sphinx moths (Pachysphinx modesta Harris). Eight aspen clones were established from root cuttings collected in the field and grown for two years in a common garden. Leaf tissues were assayed for water, nitrogen, total nonstructural carbohydrates, condensed tannins, and phenolic glycosides. Both long- and short-term feeding trials were conducted to evaluate the effects of foliage quality on insect performance. Chemical analyses showed that concentrations of phytochemicals varied significantly among aspen clones, and that such variation was greater for secondary metabolites than for primary metabolites. Performance of both insect species varied among aspen clones and was negatively correlated with foliar phenolic glycoside concentrations. Comparison of results from this and an earlier study with the same plants indicates that genetic factors influence both clonal variation in secondary chemistry and phenological expression of such variation through time.
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