PROCEEDINGS: Index of Abstracts

VARIABLE PERFORMANCE OF OUTBREAK DEFOLIATORS ON ASPEN CLONES EXPOSED TO ELEVATED CO₂ AND O₃

Daniel A. Herms-1, William J. Mattson-2, David N. Karowe-3, Mark D. Coleman-4, Terry M. Trier-5, Bruce A. Birr-2, and J. G. Isebrands-4

1-The Dow Gardens, 1018 W. Main St., Midland, MI 48640. 2-USDA North Central Forest Experiment Station, 1407 S. Harrison Rd., East Lansing, MI 48823. 3-Department of Biology, Virginia Commonwealth University, Richmond, VA 23234. 4-USDA North Central Forest Experiment Station, P.O. Box 898, Rhinelander, WI 54501. 5-Department of Entomology, Michigan State University, East Lansing, MI 48824.

Abstract: Increasing atmospheric concentrations of ozone and CO₂ affect many aspects of tree physiology. However, their effects on tree resistance to insects have received relatively little attention. The objectives of this study were to test the effects of elevated CO₂ and ozone on the resistance of three quaking aspen (Populus tremuloides) clones (216, 259, and 271) to first and fourth instars of four Lepidoptera species: gypsy moth (Lymantria dispar), forest tent caterpillar (Malacosoma disstria), large aspen tortrix (Choristoneura conflictana), and whitemarked tussock moth (Orgyia leucostigma). Larval survival, growth rates, and nutritional indices were quantified. There were no treatment effects on larval survival. Elevated CO₂ decreased the growth rates of both instars of all species, except that of first instar forest tent caterpillar on aspen clone 216, which was increased. Elevated ozone increased the growth of first and fourth instars of all insect species tested. The treatment effects on growth rate were generally caused by their effects on the ability of larvae to convert digested food to biomass (ECD). Elevated ozone increased ECD. The effects of elevated CO₂ on ECD were clone dependent: elevated CO₂ decreased ECD on clones 271 and 259, but increased ECD on clone 216. Ozone had no effect on larval consumption rates. Elevated CO₂ decreased the consumption rate of large aspen tortrix but had no effect on the other species. This contrasts with other studies, in which elevated CO₂ generally increased insect consumption. There were no statistically significant interactions between the CO₂ and ozone treatments for any of the variables measured.