Spring Larval Dispersal of the Western Spruce Budworm (Lepidoptera: Tortricidae) in North-Central Washington 1

Abstract
Vertical distribution of spring dispersal activity within a stand canopy was determined by trap catch at 2-day intervals. The 10-m traps consistently caught more larvae than the 6-, 2-, and 0.5-m traps except during inclement weather. A partial explanation is the filtering effect of adjacent tree crowns on the dispersing larvae before they reach the lower traps. Most larvae caught by the 2- and O.5-m traps would be lost to the system. Dispersal of 3rd and 4th instars represented about 38% of the total trap catch, indicating greater off-tree dispersal than normally expected for these instars. An explanation based on asynchrony of host and budworm is suggested.

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