No description available.

The connection between variable synchrony of insect eclosion with host budburst and variability in insect densities was investigated. Experiments with gypsy moth (Lymantria dispar L.) larvae determined the duration of acceptable foliage after budbreak of nine hardwood species. Four competing conceptual models of environmental influences on the timing of budburst were compared and evaluated. The best budburst model was combined with an eclosion model to estimate the frequency of asynchrony and its correlation with density. Synchrony with budburst has a smaller effect than weather after hatch, on the population size of the gypsy moth, but neither is the driving force behind density changes. However, comparison of traits of 300 species of Macrolepidoptera showed that 50% of outbreak species, but only 24% of nonoutbreak species begin feeding at the time of budburst; this suggests a stronger relation between synchrony and population dynamics than was found with the gypsy moth.

No description available.

Data for this study were collected by the US Forest Service and the Pennsylvania Bureau of Forestry on nearly 600 plots in central Pennsylvania. Tree and stand characteristics recorded between 1978 and 1985 include estimates of percent defoliation on individual trees. Logistic regression using maximum likelihood estimation was employed to model individual-tree mortality of 15 species in central Pennsylvania that had been defoliated by the gypsy moth. Defoliation was estimated to the nearest ten percent for individual trees. Other variables used for prediction included stand basal area and an individual-tree relative basal area index. Success ranged from no fit for three of the species to an R value (a derivation of Akaike's information criterion) of .613 for white oak. The inclusion of defoliation in the models had a varied effect. For four of the species percent defoliation was not significant. For hickory and white oak respectively, percent defoliation raised the R value by .305 and .290 percentage points. As many as five models for each species were developed: one or two models with no defoliation measure in the model and one each for one, two or three consecutive years of defoliation measures. A beta and gamma function were used to model individual· tree basal area growth for the same 15 species. The models were fit using nonlinear least squares. Variables used include the relative basal area index, stand basal area, site index and a defoliation index that incorporated three years of individual-tree, percent defoliation. The beta and gamma functions fit equally well with values of (1 - relative mean square error) ranging from .1967 to .6290. Results for both models are presented for each species. The defoliation index was a significant variable for five of the fifteen species: white, chestnut, red, and black oak and sassafras. / Master of Science

I investigated the effect of defoliation by the gypsy moth, Lymantria dispar L. (Lepidoptera: Lymantriidae) on the radial growth of tree species that differ in their acceptability as hosts for gypsy moth larvae. Annual growth rings were measured from 1950 to 1992 on increment cores taken from three species: red oak (Quercus rubra L.), a preferred species, sugar maple (Acer saccharum Marsh.), an acceptable species, and white ash (Fraxinus americana L.), an avoided species. The number of gypsy moth larvae on these same individual trees had already been recorded from 1979 to 1992. To remove the potentially-confounding effects of climate on radial growth, I developed regression models of growth on climate in a pre-gypsy moth period (1950 to 1975), and then used these models to predict growth in a post-gypsy moth period (1978 to 1992). The residuals from these growth models were then examined with respect to gypsy moth numbers. (Abstract shortened by UMI.)

No description available.