Genetically based differences in susceptibility of white spruce to the spruce bud moth

Abstract

The susceptibility of white spruce, Piceaglauca (Moench) Voss, leaders to damage by the spruce bud moth, Zeirapheracanadensis Mut. & Free., was assessed for 72 half-sib families at four half-sib family test sites and in one seedling seed orchard in New Brunswick. Trees of intermediate height (1.5–3.75 m) were the most damaged, and damage in one year was positively correlated to damage in the next. During 2 consecutive years, half-sib family explained only 1% of the variation in damage when all four test sites were analysed together. However, half-sib family explained between 2.9 and 7.9% of the variation in damage at individual sites. At the four test sites, mean growth reductions of trees in the two most susceptible families were estimated to be approximately 30% higher than those of trees in the two least susceptible families. When all 72 families were ranked with respect to height, trees in the most susceptible and least susceptible families were ranked very poorly and highly, respectively. This suggested that trees in more susceptible families were smaller because of damage by the spruce bud moth. However, this pattern was observed at all sites, including one where bud moth damage was negligible. Thus even in the absence of damage by the spruce bud moth, trees in these least susceptible families had a greater growth rate, in terms of height, than trees in the most susceptible families. This indicates that selection for plant traits reducing susceptibility to bud moth may be compatible with breeding programs attempting to improve height growth. Implications of these results for tree improvement programs are discussed.

Serotinous cones of Cupressus sempervirens provide viable seeds in spite of high seed predation

“…20 and 6). The possibility that the plant genotype affects the susceptibility to insects exists [24, and references therein] and has been verified also in forest pests [6,10,17], including cone and seed insects [26].…”

Mechanisms of resistance of white spruce to the spruce bud moth

“…Evaluations in four half-sib family tests demonstrated that a significant proportion of damage by the bud moth to young white spruce trees was attributable to tree genotype (Quiring et al 1991). Moreover, trees in some half-sib families that were among the least damaged and tallest in sites with high bud moth densities ( Fig.…”

“…Moreover, trees in some half-sib families that were among the least damaged and tallest in sites with high bud moth densities ( Fig. 1) were also among the tallest in sites with low pest densities, indicating that selection for resistance to bud moth may be compatible with selection for tree growth (Quiring et al 1991). Subsequent studies have demonstrated that there are several genetically-based mechanisms responsible for reducing the susceptibility of white spruce trees to the spruce bud moth.…”

“…the bud moth to adapt to resistant trees will be reduced if: i) the proportion of white spruce that are resistant in any one area is limited; ii) there are several mechanisms of resistance; iii) if the length of exposure to the selective pressure is short (Gould 1988;Raffa 1989;Quiring et al 1991). Consideration of all three of these factors suggests that the bud moth would not adapt quickly to resistant trees if they were judiciously integrated into management programs.…”

“…Finally, recent work by Ostaff (1995) has shown that bud moth populations decrease to very low and economically insignificant levels after crown closure, which occurs when trees are approximately 12-15 years old. Thus, as the spruce bud moth does not usually damage trees < 1 m tall (Quiring et al 1991), white spruce trees in plantations are usually only susceptible to bud moth for approximately 7-10 years (= 7-10 generations).…”