Responses of trembling aspen ( Populus tremuloides ) phytochemistry and aspen blotch leafminer ( Phyllonorycter tremuloidiella ) performance to elevated levels of atmospheric CO ₂ and O ₃

Abstract 1 This research was conducted at the Aspen FACE (Free Air CO 2 Enrichment) site located in northern Wisconsin, U.S.A. where trembling aspen ( Populus tremuloides Michaux) trees were exposed to one of four atmospheric treatments: elevated carbon dioxide (CO 2 ; 560 µL/L), elevated ozone (O 3 ; ambient × 1.5), elevated CO 2 and O 3 , or ambient air. We evaluated the effects of these fumigants on aspen foliar quality and the performance of aspen blotch leafminer ( Phyllonorycter tremuloidiella Braun). 2 CO 2 and O 3 each affected foliar quality, with the major changes consisting of an 11% reduction in nitrogen under elevated CO 2 and a 20% reduction in tremulacin under elevated O 3 . In the CO 2 + O 3 treatment, nitrogen levels were reduced by 15% and CO 2 ameliorated the O 3 ‐mediated reduction in tremulacin levels. 3 Phyllonorycter tremuloidiella were allowed to colonize trees naturally. Elevated CO 2 and O 3 reduced colonization rates by 42 and 49% relative to ambient CO 2 and O 3 , respectively. The only effect of fumigation treatments on larval performance occurred under elevated O 3 , where male development time and larval consumption increased by 8 and 28%, respectively, over insects reared under ambient O 3 . 4 These data demonstrate that the individual and combined effects of CO 2 and O 3 can alter aspen foliar chemistry and that these alterations in foliar chemistry produce little to no change in larval performance. However, both CO 2 and O 3 greatly reduced oviposition. In order to ascertain the full effects of CO 2 and O 3 on insect performance, future studies should address both population‐ and individual‐level characteristics.