Direct Measurement of Spruce Budworm (Lepidoptera: Tortricidae) Larval Dispersal in Forest Stands

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Abstract
Dispersal of lst- and 2nd-instar larvae of Choristoneura fumiferana (Clemens) within and between host tree crowns, as well as losses due to landing of larvae on the ground, were observed and quantified with the aid of sticky traps. It was found that 1st-instar larvae disperse mostly within the crown, whereas 2nd-instar larvae disperse more readily between crowns. There was no change in density or vertical distribution of airborne larvae with distance from host trees. Estimated losses due to the landing of 2nd-instar larvae on the ground were very low and depend on stand density and composition. Such losses are partly compensated for by larvae crawling back up the trunk of host trees.