Effect of host tree condition on the fitness of the introduced brown spruce longhorn beetle, Tetropium fuscum (Fabr.), in Canada

The brown spruce longhorn beetle (BSLB), Tetropium fuscum (Fabr.), a European cerambycid, was discovered in Halifax, Nova Scotia in 1999.  The BSLB primarily infests weakened Norway spruce, Picea abies (L.) Karst., in Europe, but in Canada has been reported to infest seemingly healthy red spruce, Picea rubens Sarg, white spruce, P. glauca (Moench) Voss, and black spruce, P. mariana (Mill) B.S.P.  Red spruce is considered at risk in North America and preliminary research suggests that red spruce of low vigour is more susceptible to colonization by BSLB than trees of high vigour. Despite these findings, there is still considerable debate as to whether BSLB can infest healthy trees in Canada.

This research was conducted in Halifax, NS, and evaluates the effect of host tree condition on BSLB fitness. We are also analyzing stage specific mortality, including mortality due to natural enemies.  We caged mated BSLB pairs on red spruce trees of varying condition (healthy, girdled and recently cut) and allowed them to oviposit.  Eggs are laid under bark scales and early instar larvae bore into the phloem.  A bolt from each study tree will be reared in the laboratory to determine adult emergence rate and potential fecundity of females emerging from hosts of varying condition. Subsequent dissection of bolts will allow an evaluation of stage-specific mortality rates and factors.  This research will significantly improve our limited understanding of BSLB population ecology in Canada, and will also contribute to the development of BSLB population growth models.