Influence of Host Tree Condition on the Performance ofTetropium fuscum(Coleoptera: Cerambycidae)

Abstract

Tetropium fuscum (F.) attacks weakened Norway spruce, Picea abies (L.) Karst., in its native Europe and may colonize healthy spruce in Nova Scotia, Canada. We used manipulative field experiments to evaluate: 1) the development of T. fuscum on apparently healthy red spruce (Picea rubens Sarg.) in Nova Scotia; 2) the influence of red spruce physiological condition (healthy, girdled or cut) on T. fuscum performance; and 3) the impact of natural enemies and competitors on T. fuscum performance when developing on trees of varying condition. Tetropium fuscum successfully developed on healthy red spruce. Survival was higher on healthy than on girdled or cut trees when larvae were exposed to natural enemies and competitors. The benefits of reduced competition and parasitism on healthy trees appeared to compensate for any reductions in nutritional quality, increase in host resistance, or both. In contrast, when T. fuscum were protected from natural enemies, apparent survival was highest on girdled trees. Tetropium fuscum development took longer on healthy than on cut or girdled trees, and emerged adults were largest on healthy trees. The disparities in adult sizes among the three treatments may mean that healthy trees are more nutritious. Alternatively, the differences may indicate that a greater amount of time was spent feeding in healthy than in girdled or cut trees. Tree condition appears to have a direct impact on the success of T. fuscum, influencing survival, development time, and adult size, and may mediate the impact of natural enemies and competitors, further affecting T. fuscum performance.

Evaluating Seasonal Variation in Bottom-Up and Top-Down Forces and Their Impact on an Exotic Wood Borer,Tetropium fuscum(Coleoptera: Cerambycidae)

“…We randomly assigned each tree to one of two tree condition treatments, girdled or healthy (unmanipulated), and to one of three groups representing different T. fuscum attack dates. To experimentally stress trees, we used a chainsaw to girdle trees 30 cm above the tree base, Ϸ2.5 cm deep into the phloem and outer sapwood, on 6 May (12 trees), 20 May (9 trees), or 3 June 2009 (9 trees), similar to Flaherty et al (2011).…”

“…We protected either the top or the bottom group of eggs (randomly selected) from natural enemies and competitors by fastening a Þne-mesh cage (Flaherty et al 2011) 17.5 cm above and below the eggs on each tree. We fastened cages on each tree in early May, before girdling, and they remained on trees until the tree was cut or until 14 April 2010, when they were replaced with emergence cages (see T. fuscum Survival, Size, and Development).…”

“…We predicted that T. fuscum would perform better on stressed than on healthy trees, because of reductions in host defenses and improved nutrition in stressed compared with healthy trees. However, we also predicted that T. fuscum developing in stressed trees may experience higher rates of parasitism and competition, reducing their performance (Flaherty et al 2011). Finally, we evaluated seasonal variation in bottomÐ up and topÐ down forces by manipulating the timing when T. fuscum attack host trees.…”

Evolving symbioses between insects and fungi that kill trees in Canada: new threats associated with invasive organisms

“…The beetle is able to disperse via flight and by human-assisted dispersal through the movement of infested spruce products; therefore, the movement of high-risk forest products is restricted by ministerial order (Canadian Food Inspection Agency 2014). Further research on host preference by T. fuscum has shown that the beetle prefers stressed trees over healthy trees (Flaherty et al 2011(Flaherty et al , 2013, thus lowering the risk profile associated with healthy red spruce, and this has had a bearing on the decision of Canadian Food Inspection Agency to shift to a containment strategy (Canadian Food Inspection Agency 2014).…”

Phoresy of Trichouropoda shcherbakae Hirschmann, 1972 (Acari: Mesostigmata) on beetles of the genus Tetropium Kirby, 1837 (Coleoptera: Cerambycidae) in Białowieża Forest, Poland

“…Beetles of the genus Tetropium inhabit weakened, dying and dead trees, but they are not classified as dangerous forest pests (three species are classified as quarantine pests) [22,24,25]. Adults of T. fuscum appear in the Białowieża Forest around mid-May, and the last specimens can be found even in July.…”