Treesearch

A technique is described to relate seasonal development of buds of Douglas-fir, Pseudotsuga menziesii (Mirt.) Franco, to larval emergence and survival of western spruce budworm (Choristoneura occidentalis Freeman) (Tortricidae). Losses of larvae due to asynchrony of emergence and bud swelling and the reduced protection of the bud following flush is illustrated.

The impact of the budworm on trees and stands and conditions that lead to susceptible and vulnerable stands are discussed. Long-term and short-term options dealing with the spruce budworm problem are presented. Examples of questions that plant-animal interaction research have answered are presented in the following scenarios: ( 1) can the release phase of an outbreak be detected, (2) can spruce budworm impact be predicted, (3) are regionwide rating systems accurate, and (4) what, if any, relationships exist between site classification units and spruce budworm impact.

Site conditions strongly influence where gypsy moth defohation will occur. In New England, where gypsy moths and foresta have interacted for over a century, some foreats have had a history of repeated defoliation while others have been defo1iated only rarely. The often defohated or susceptible forests characteristically grow on dry sitea such as rocky ridges or deep sands. In many esses, they have been disturbed - sometlmes frequently - by fire, Wind. snow, or ice storms. The trees in these forests. mainly dry-site oaks. often are highly favored as food by gypsy moths. are slow growing,...

Although it may soon be possible to alter stand foliage quality and thus reduce budworm reproductivity, the impact of such changes on the budworm-forest system remains unclear. There are currently a number of hypotheses concerning the key biological mechanisms which drive the budworm-forest system. The possible effects of changes in foliage quality are examined for four such alternative hypotheses. Each hypothesis suggests that in the short-term reducing foliage quality will lengthen the interval between out breaks, increase the rate of stand wood volume production, and increase outbreak...

A differential equation model of gypsy moth abundance, average larval dry weight, and food abundance was used to analyze the effects of changes in foliar chemistry on the net per capita rate of increase in a gypsy moth population. If relative consumption rate per larva is unaffected by herbivory, a reduction in the nutritional value of foliage reduces the net rate of increase at relatively low larval densities, and increases the larval density needed to bring about starvation. This result is achieved by reducing larval assimilation efficiency, or by increasing larval death rate, or both,...

Two Maine spruce-fir stands having different soils were sampled to determine the relationship between spruce budworm weight (fecundity) and foliage quality. Although much of the variation in budworm weight was attributable to other factors, significant correlations between budworm weight and multiple foliar nutrient concentration variables suggest that foliage quality altering silvicultural practices such as fertilization may stimulate populations of the spruce budworm.

This study evaluated effects of fertilization of young western larch stands on western spruce budworm feeding in Montana. Various combinations of nitrogen, phosphorus, and potassium resulted in nearly double the amount of feeding by western spruce budworm larvae, with nitrogen eliciting the most response. Larch growth response to fertilization can be negated by increases in budworm feeding.

Plant chemistry alone fails to explain why most trees escape defoliation most of the time. Chemical variation in space and time, acting to enhance the effectiveness of natural enemies, may be the key. Changes and increasing variation in direct response to insect attack ("induction") may be particularly important for irruptive pests.

The Canada/U.S. Spruce Budworms Program in cooperation with the Center for Biological Control of Northeastern Forest Insects and Diseases of the Northeastern Forest Experiment Station co-sponsored this Forest Defoliator-Host Interaction Workshop.This invitational workshop was limited to investigators of the spruce bud worms and gypsy moth in the Forest Service, Canadian Forestry Service, and the University sector. The primary purpose of this workshop was to foster communication between researchers having a mutual interest and active research projects designed to understand the relationships...

The influence of host type and condition on the bioecology of gypsy moth are discussed from the viewpoint of room and board. Larval establishment was higher on preferred hosts; less than 5% migrated off them. Nonpreferred hosts lost 10-25% of larvae. Susceptibility of gypsy moth larvae to nucleopolyhedrosis virus increased following 1 or 2 years of defoliation. Survival value of insect resting locations on the host tree and in the litter are discussed in connection with risk of predation.