Host plant phenology drives risky larval dispersal in an outbreaking insect defoliator

Dispersal away from natal sites allows individuals to find suitable foraging sites to complete their development and successfully reproduce. However, the decision to disperse is risky for young larval Lepidoptera because mortality rates as they move from source to sink sites are high. Factors that drive this risky dispersal behaviour in forest landscapes by early instar larvae of outbreaking defoliators such as the eastern spruce budworm are not well understood.  We assessed dispersal behaviour of young larvae in relation to resource availability in terms of spring budburst phenology of primary and secondary host species, balsam fir and black spruce, respectively. We tested whether tree species and presence of suitable feeding sites influenced dispersal away from source branches and subsequent redistribution of insects. Laboratory experiments showed that dispersal is an active behaviour during which larvae disperse away from source trees without expanded buds, regardless of species. Est..., , , # Host plant phenology drives risky larval dispersal in an outbreaking insect defoliator

[https://doi.org/10.5061/dryad.1jwstqk20](https://doi.org/10.5061/dryad.1jwstqk20)

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We assessed dispersal behaviour of young spruce budworm larvae in relation to spring budburst phenology of primary and secondary hosts, balsam fir and black spruce, respectively. We tested whether tree species and presence of suitable feeding sites influenced dispersal away from source branches and subsequent redistribution of insects. Laboratory experiments showed that dispersal is an active behaviour during which larvae disperse away from source trees without open buds, regardless of species. Establishment on sink branches was highest when they possessed open buds and the source did not. In the field, larval dispersal was higher from black spruce than from balsam fir and larval establishment was ...