The number of the birch casebearer larvae, Coleophora fuscedinella Zeller, within white birch crowns, Betula papyrifera Marsh., decreased 70% from overwintered survivors to about 50% pupae in the population. Within a crown, the highest number occurred in the outer shell and lowest in the inner. Casebearer numbers, weighted by the number of leaf clusters, were highest in the inner shell and lowest in the outer. Among crown quarters, both unweighted and weighted numbers were generally highest in the middle two crown quarters, lowest in the bottom quarter, and variable in the top quarter.
Peaks in immigration and emigration of larvae among crown strata occurred first when third and again when fourth instar larvae were most abundant. Immigration consisted only of intra-tree crawling, but emigration consisted of intra-tree crawling, removal by predation, and larvae leaving the tree to pupate on ground vegetation.