The Effect of host tree diameter on landing rate of Tetropium fuscum (Fabr.) (Coleoptera: Cerambycidae)
LE3 .A278 2016
Bachelor of Science
The brown spruce longhorn beetle, Tetropium fuscum (Fabr.), is an invasive beetle from Europe that has been established in Nova Scotia since at least 1990. It primarily infests and kills spruce trees (Picea spp.) that exhibit low vigour or spruce that are stressed due to disturbances such as defoliation, drought, or extreme wind. Surveying has shown that beetle infestation mainly occurs in spruce with large diameters at breast height (dbh) and that spruce infestation has not been observed in trees smaller than 9 cm in dbh. Tetropium fuscum completes its entire larval development in the phloem of its host, so our hypothesis was that the beetle prefers hosts with greater phloem area and thickness i.e. trees with larger diameter. This study aimed to discern whether host tree diameter affected the landing rate of T. fuscum, as measured by the number of beetles that landed on sticky bands wrapped around the bole of P. rubens at breast height. Linear regression was used to test the relationship between tree dbh and the number of T. fuscum per square metre as well as the number of T. fuscum per tree, i.e. per sticky band. Results showed a significant positive linear relationship between dbh and T. fuscum caught per tree, but no significant relationship between dbh and T. fuscum density. If the largest trees within the dbh range test (30 cm) are the preferred hosts of T. fuscum, one would expect that the density of foraging adults would increase with dbh as well. This inconsistency might be attributed to the vigour of the trees which was positively correlated with dbh. Additionally, we investigated the effect of a power line access corridor near the study site on the landing rate of T. fuscum, as we believed that adult beetles were more inclined to forage for hosts away from the corridor where there were more potential host trees. A series of heatmaps was developed, accompanied by a linear regression of T. fuscum per square metre on each band versus proximity to the corridor. There was little evidence that proximity to the corridor affected T. fuscum landing rate. Overall, we recommend further research on the relationship between tree vigour and the host choice of T. fuscum.
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