PATTERNS OF OCCURRENCE AND NEW SAMPLING IMPLICATIONS FOR INSTAR-IV WESTERN SPRUCE BUDWORM (LEPIDOPTERA, TORTRICIDAE)

This study examines relations of western spruce budworm (Choristoneura occidentalis Free.) larval distribution on terminal tips, whole branc hes, among crown strata (vertical crown thirds), and within and among whole trees. Study sites were in Washington, Oregon, Idaho, Montana, a nd New Mexico and represented 63 plot-yr of data. A range of densities from <1.0 to >600 larvae per m2 of foliage on midcrown terminal tips were observed. We validated and expanded on earlier published descript ions of intratree and intertree distribution of larvae as they influen ced sampling schemes. Larval density on nominal 45 cm terminal tips in the lower crown-third were slightly better predictors of whole-tree d ensity than were midcrown tips. Therefore, we propose the use of a two -tip sample from the middle of the lower crown-third of each sample tr ee. Equations are given to determine the number of trees to sample for desired precisions and confidence levels. We provide equations descri bing relations between larval densities on branch tips and whole branc hes in vertical crown-thirds, and their relation to whole-tree density .