Effects of genotype, elevated CO and elevated O on aspen phytochemistry and aspen leaf beetle Chrysomela crotchi performance

摘要

1 Trembling aspen Populus tremuloides Michaux is an important forest species in the Great Lakes region and displays tremendous genetic variation in foliar chemistry. Elevated carbon dioxide (CO) and ozone (O) may also influence phytochemistry and thereby alter the performance of insect herbivores such as the aspen leaf beetle Chrysomela crotchi Brown. 2 The present study aimed to relate genetic- and atmospheric-based variation in aspen phytochemistry to C. crotchi performance (larval development time, adult mass, survivorship). The experiment was conducted at the Aspen Free-Air CO Enrichment (FACE) site in northern Wisconsin. Beetles were reared on three aspen genotypes under elevated CO and/or O. Leaves were collected to determine chemical characteristics. 3 The foliage exhibited significant variation in nitrogen, condensed tannins and phenolic glycosides among genotypes. CO and O, however, had little effect on phytochemistry. Nonetheless, elevated CO decreased beetle performance on one aspen genotype and had inconsistent effects on beetles reared on two other genotypes. Elevated O decreased beetle performance, especially for beetles reared on an O-sensitive genotype. Regression analyses indicated that phenolic glycosides and nitrogen explain a substantial amount (27-45%) of the variation in herbivore performance. 4 By contrast to the negative effects that are typically observed with generalist herbivores, aspen leaf beetles appear to benefit from phenolic glycosides, chemical components that are largely genetically-determined in aspen. The results obtained in the present study indicate that host genetic variation and atmospheric concentrations of greenhouse gases will be important factors in the performance of specialist herbivores, such as C. crotchi, in future climates.