Rapid wound-induced resistance in white birch (Betula pubescens) foliage to the geometrid Epirrita autumnata: a comparison of trees and moths within and outside the outbreak range of the moth.

Two strains of a geometrid defoliator, Epirrita autumnata, were used in bioassays to test existence and relative efficacy of rapid, wound-induced foliage resistance in two provenances of the white birch. One birch and one moth strain originated in the outbreak range of the moth and another outside it. Both birch provenances responded to manual leaf damage by changes in foliage quality which significantly retarded growth of the insects, reducing their pupal weights and protracting larval periods. Leaves which were previously damaged were lower quality as Epirrita food than adjacent intact leaves. Both of them were lower quality than intact leaves without damaged leaves nearby. Because of variance between years in the efficacy of the response, and because of different transfer distances of the provenances to the common garden where the experiments were performed, we could not ascertain whether there is any overall difference in the efficacy of rapid inducible responses between the provenances. Both moth strains were affected by wound-induced deterioration in foliage quality. There were no differences in how the moth strains experienced inducible resistance in the two birch provenances. Moths achieved relatively higher pupal weights on the birch provenance matching their origin. Moths from the outbreak range completed their larval period in a shorter time and pupated in a smaller size and, due to dependence of fecundity on size, had a lower potential rate of increase than insects outside the outbreak range.