Susceptibility of pine plantations to attack by the pine shoot beetle (Tomicus piniperda) in southern Ontario

The pine shoot beetle, Tomicus piniperda (L.) (Coleoptera: Scolytidae), was first discovered in North America in 1992, and by the late 1990s it was associated with tree mortality and stand decline throughout southern Ontario. To assess whether this beetle was capable of killing vigorous trees (a primary pest) or would kill only trees already stressed (a secondary pest), we surveyed 43 sites of varying Scots pine (Pinus sylvestris L.), red pine (Pinus resinosa Ait.), and jack pine (Pinus banksiana Lamb.) composition. Specifically, our objective was to determine the relationship between tree and site characteristics and the number of stem and shoot attacks by T. piniperda in southern Ontario. An abundance of recently dead and low-vigour pine trees increased susceptibility of sites to stem and shoot attacks by T. piniperda. Significant negative linear relationships were detected between the number of beetle attacks and the mean height, age, diameter at breast height, basal area, canopy cover, duff depth, and radial growth increments. Pure red pine sites had significantly fewer attacks than sites of pure Scots pine and mixed jack pine, which was attributed to differences in tree vigour and forest management. Tomicus piniperda appears to be a secondary bark beetle in southern Ontario, successfully colonizing only recently dead pine trees or trees suffering from stress.