PROCEEDINGS: Index of Abstracts
VARIABLE PERFORMANCE OF OUTBREAK DEFOLIATORS ON
ASPEN CLONES EXPOSED TO ELEVATED CO2 AND O3
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,
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.