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Abstract
Increasing atmospheric concentrations of ozone and CO
2 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 CO
2 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 confictana), and whitemarked tussock moth (
Orgyia leucostigma). Larval survival, growth rates, and nutritional indices were quantified. There were no treatment effects on larval survival. Elevated CO
2 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 CO
2 on ECD were clone dependent: elevated CO
2 decreased ECD on clones 271 and 259, but increased ECD on clone 216. Ozone had no effect on larval consumption rates. Elevated CO
2 decreased the consumption rate of large aspen tortrix but had no effect on the other species. This contrasts with other studies, in which elevated CO
2 generally increased insect consumption. There were no statistically significant interactions between the CO
2 and ozone treatments for any of the variables measured.
Parent Publication
Citation
Herms, Daniel A.; Mattson, William J.; Karowe, David N.; Coleman, Mark D.; Trier, Terry M.; Birr, Bruce A.; Isebrands, J. G. 1996. Variable performance of outbreak defoliators on aspen clones exposed to elevated CO
2 and O
3. In: Hom, John; Birdsey, Richard; O''Brian, Kelly, eds. Proceedings 1995 meeting of the northern global change program; Gen. Tech. Rep. NE-214. Radnor, PA: U. S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station: 43-55.