Behaviors of Western Spruce Budworm Moths (Choristoneura occidentalis) as Defences Against Bat Predation

We investigated potential defense behaviors of adult western spruce budworm (Choristoneura occidentalis), a non-auditive lepidopteran, against bat predation. Although western spruce budworm moths started to fly before sunset, earlier than many species of moths, temporal isolation of flying moths from foraging bats was incomplete as moths were most active after sunset once bats were foraging. Flying C. occidentalis were most active close to their host trees, and thus were isolated from some bat activity because vegetation limits foraging by some bats. Moths mostly flew near the tops of trees, an area that may have a high predation pressure from bats. Resting western spruce budworm spent little time fluttering their wings or crawling, behaviors that are used as cues by gleaning bats. The outbreak nature of this species, in which large numbers of moths are active at one time, may allow dilution effects to reduce predation risk.