Nineteen balsam fir trees, Abies balsamea, from five spruce-fir stands in Michigan\u27s Upper Peninsula, were used to study egg mass densities and distributions. Ten were used to study the effects of branch size on mass density estimates. The foliage surface area and the number of new egg masses spruce budworm, Choristoneura fumiferana, were determined for each branch, and the top of each tree and (or) the branch segment of interest. We determined the effects of the bias and the variance of the estimator, of sampling different parts of the tree, and of sampling different size branches. Points that should be considered when estimating spruce budworm egg mass densities on balsam fir were identified. Generally, sampling whole branches from the mid-crown gave the most precise and accurate estimates of tree egg mass density
