Site factors and management influence short‐term host resistance to spruce budworm, Choristoneura fumiferana (Clem.), in a species‐specific manner

Abstract

Thinning reduced balsam fir resistance to spruce budworm defoliation. This response is due to increased defoliation linked to reduction in concentrations of certain monoterpenes, and a decrease in foliage production, except on hydric drainage, demonstrating the importance of drainage class to tree resistance. The results suggest that the use of Bacillus thuringiensis might be required when conducting stand thinning during spruce budworm outbreaks.

Indirect host-mediated effects of an exotic phloem-sap feeder on a native defoliator of balsam fir

“…et al (2014), who reported no influence of thinning on tree growth in the same stands. However, they contrast with previous studies that have repeatedly demonstrated positive effects of thinning on tree growth and on tolerance of budworm attack (e.g., Bauce, 1996;Fuentealba and Bauce, 2012) and have therefore suggested thinning as a management tool to reduce the impact of budworm outbreaks (Crook et al, 1979;Bauce, 1996;Hennigar et al, 2011;Fuentealba and Bauce, 2012). We suspect this difference in the importance of thinning arises because most previous studies have conducted experiments within five years of thinning, whereas our work took place $20 years after thinning (in stands >40 years old).…”

“…Concentrations of N have previously been related to budworm pupal weight (Mattson et al, 1991), and although Clancy and King (1993) reported a negative effect of Mg on the performance of western spruce budworm (C. occidentalis), the lowest concentration they tested was well above the average concentration measured in our study. Trees with high levels of monoterpenes are more resistant to budworm attack (e.g., Chen et al, 2002;Fuentealba and Bauce, 2012) and budworm larvae fed monoterpene-rich foliage pupate at lower weight (Mattson et al, 1991; and for C. occidentalis, Redak and Cates, 1984;Cates et al, 1987). Unexpectedly, though, in our stands decreases in branch growth with gout were not accompanied by changes in measured chemistry of current-year foliage (Grégoire et al, 2014).…”

Spruce budworm biological and nutritional performance responses to varying levels of monoterpenes

“…Concentrations of these compounds, like others present in the host plant foliage, are subject to spatial and temporal change. It is well known that terpenoid concentrations in foliar tissues generally increase with light intensity (Spring et al 1986, Bryant et al 1987, Gref & Tenow 1987, with nutrient availability (Björkman et al 1998), and following stand thinning, for example, in balsam fir (Bauce 1996, Lamontagne et al 2000, Fuentealba & Bauce 2012. Bauce et al (1994) showed that monoterpenes are positively correlated with the strong resistance offered by young balsam fir trees against budworm attack, compared to mature individuals.…”

Short‐term influence of partial cutting on hemlock looper (Lepidoptera:Geometridae) parasitism

“…For example, thinning is suggested to reduce damage caused by spruce budworm Choristoneura fumiferana (Clemens), (Crook et al ., ; Bauce, ; Bauce et al ., ; Fuentealba & Bauce, ) and western spruce budworm C. occidentalis Freeman (Mason et al ., ). Fuentealba and Bauce () suggest that thinning might reduce some negative impacts of the spruce budworm up to 3 years after treatment through an increase of foliar production. However, in the short term (1 year after treatments), tree resistance to spruce budworm defoliation is reduced as a result of its negative impact on host foliar monoterpene defence compounds (Bauce, ; Fuentealba & Bauce, ).…”

“…Fuentealba and Bauce () suggest that thinning might reduce some negative impacts of the spruce budworm up to 3 years after treatment through an increase of foliar production. However, in the short term (1 year after treatments), tree resistance to spruce budworm defoliation is reduced as a result of its negative impact on host foliar monoterpene defence compounds (Bauce, ; Fuentealba & Bauce, ). Altering stand structure may also affect the relationship between defoliating insects and their natural enemies.…”