Emma Despland

 - Abstract: Ballooning dispersal by second-instar spruce budworm (Choristoneura fumiferana) away from the tree on which they emerge from diapause is very risky. We monitored this dispersal behaviour in relation to spring budburst phenology of primary and secondary host trees, balsam fir and black spruce, respectively. Specifically, we tested whether tree species and presence of buds available for feeding influenced the choice to disperse away from source branches and ensuing redistribution of insects. Laboratory experiments showed that dispersal is an active behaviour during which larvae leave source trees without open buds, regardless of species.In the field, larval dispersal was higher from black spruce than from balsam fir, as black spruce has later budbreak phenology. These findings are the first to show how risky dispersal behaviour in larval Lepidoptera is facultative and is determined by local food availability.