DISTRIBUTION OF OVERWINTERING BIRCH CASEBEARER LARVAE, COLEOPHORA FUSCEDINELLA, ON WHITE BIRCH (LEPIDOPTERA: COLEOPHORIDAE)

Abstract

AbstractThe majority (about 94%) of birch casebearer larvae, Coleophora fuscedinella Zeller, abandon the leaves in the fall and attach their case to the bark surface at spurs, at the base of buds, and at twig crotches. Casebearer populations were studied in six white birch, Betula papyrifera Marsh., stands of 3 m to 6 m in height. An average of 50% of overwintering population of the birch casebearer occurred within 50 cm of the crown periphery of the middle half of the crown. This proportion was the same at the three population densities studied: 2,000, 10,000, and 20,000 cases per tree. Intra-tree distribution differed significantly between stands and between years and was modified when there were more than 3,000 larvae in a tree. However, the relation between log10 (cases + 1) at midcrown and the whole tree was consistent and usually explained more than 85% of the variance. For all population densities, the number of casebearers in the tree could be estimated from a sample of the crown. To preserve the form and aesthetic value of trees, the sample should comprise spurs or crotches and not a crown sector as used in this study.