Ontogeny and stand condition influence the dispersal behavior of a defoliating specialist caterpillar

A 4-yr field study was carried out to study the dispersal behavior of young larvae of the eastern spruce budworm (Choristoneura fumiferana Clemens) (Lepidoptera: Tortricidae) within and between crowns of balsam fir (Abies balsamea (L.) Miller), through the peak to decline of an outbreak. Newly hatched neonates, searching for overwintering sites in the fall, were frequently captured in sticky traps as they dispersed via "ballooning" (on silken threads) between and within tree crowns. A relatively small proportion of neonates were also captured on sticky tapes as they walked down the trunk toward the lower crown, where most larvae overwinter. In the spring, second-instar larvae (L2) searching for feeding sites also ballooned within and between trees, but were also frequently captured on traps on all crown levels as they walked up trunks. Over the course of our study, defoliation in our study trees increased, and current-year shoot availability decreased significantly, perhaps influencing L2 in search of food to disperse more frequently among hosts via ballooning. Results of our study suggest that the foraging priorities of neonates and L2 significantly influence larval dispersal behaviors and that spruce budworm larvae may vary behaviors in response to changing host condition during an outbreak.