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RECENT ADVANCES IN RESEARCH ON WHITE PINE WEEVIL ATTACNG
SPRUCES IN BRITISH COLUMBIA
G.K. KISS I, A.D. YANCHUK 2, R.I. ALFARO a, J.E. CARLSON 4, and J.F. MANVILLE 3
1British Columbia Forest Service, Kalamalka Forestry Centre, Vernon, British Columbia, Canada
2British Columbia Forest Service, Research Branch, Victoria, British Columbia, Canada
3Canadian Forest Service, Pacific Research Centre, Victoria, British Columbia, Canada
4University of British Columbia, Biotechnology Laboratory, Vancouver, British Columbia, Canada
INTRODUCTION
Interior spruce (a collective term for white spruce, Picea gIauca (Moench) Voss; Engelmann spruce, Picea
engelmanni Parry, and their varying degrees of hybrids) is a very important timber resource for the province of British
Columbia. Over 100 million interior spruce seedlings are planted annually. An estimated 1.38 billion seedlings have been
planted to date, and the total number of hectares planted in spruce is over 1.3 million.
White pine weevil, Pissodes strobi Peck, is a major cause of Sitka spruce, Picea sitchensis (Bong.) Carr., plantation
failure in coastal British Columbia, Washington, and Oregon (McMullen 1976; Furniss and Carolin 1977; MacSiurtain I981,
Alfaro 1982, 1989). This pest is also becoming an important menace to interior spruce plantations, causing considerable
damage to both yield and quality of product (Cozens 1983, Taylor et al. 1991).
Adult weevils overwinter in the duff layer of the forest floor and begin laying their eggs in the bark of young spruce
trees (generally 3-30 years old) near the tip of the previous ye.ar's shoot in early summer. Young weevil larvae feed on the
phloem of the leader, moving downwards in the process (Silver 1968). Once a feeding ring is formed, the leader of the tree
dies. In their downward movement, the larvae can destroy up to 4 years of growth. Literature sources refer to the successful
colonization of the leader as weevil attack; this terminology will be maintained in this report. Repeated leader destruction
causes loss of height growth and stem deformities, which leads to quality reduction (Alfaro 1989 and 1992).
Selection of spruce varieties genetically resistant to weevil damage is a potential tool for the reduction of weevil
damage in future plantations. Genetic resistance could manifest itself in several forms. Morphological and anatomical
differences could make certain trees less susceptible to feeding, ovipositioning, and to the development of the larvae (Plank
and Gerhold 1965, Stroh and Gerhold 1965). Another possible resistance mechanism consists of variations in the chemical
composition of resistant trees that make them less attractive to weevils. Phagostimulants may be lacking in some trees,
which can render them less attractive to weevils. Alternately, the presence of feeding repellents, deterrents, or toxic compounds
may provide an effective defense mechanism (van Buijtenen and Santamour 1972; Bridgen et al. 1979; Alfaxo 1980;
Alfaro et al. 1980, 1984; Alfaro and Borden 1982, 1985; Wilkinson 1985; Brooks et al. 1987 a, b).
The impact of weevil damage could be mitigated by the ability of the trees to recover from the attack (Painter 1951 ).
Tolerant trees are more likely to overcome the effect of attacks and will suffer less growth and quality loss. This depends
largely on the ability of one of the lateral branches to gain apical dominance quickly after the leader has been killed. Trees
lacking this ability will develop multiple leaders (forks) and often are stunted.
Evaluation of various trials in British Columbia provided strong evidence for genetic variation in susceptibility for
weevil damage in both Sitka spruce (Ying 1991, Alfaro and Ying 1990) and interior spruce (Kiss and Yanchuk 1991).
Mattson, W.J., NiemelL P., and Rousi, M., eds. 1996. Dynamics of forest herbivory: quest for pattern and principle.
USDA For. Serv. Gen. Tech. Rep. NC-183, N.C. For. Exp. Sta., St. Paul, MN 55108.
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