Past infestations of the white pine weevil in naturally regenerated spruce stands

Abstract

.M. ~i r n o t o l~~, Rene I. ~l f a r o~ and John H. ~o r d e n l Past infestations of the white pine weevil, Pissodes strobi (Peck), were reconstructed by examining standing and felled trees in naturally regenerated interior spruce stands in the McGregor Model Forest in northern B.C. Infestations were common in both the SubBoreal Spruce (SBS), wet cool (SBSwk) and very wet cool (SBSvk) biogeoclimatic subzones, demonstrating that frequent weeviling is a natural event that predates human intervention. Approximately one-third of all stem defects in 32 felled trees were verified as caused by the weevil. In the SBSwk and SBSvk 56.3% and 81.3% of felled trees contained weevil-caused defects, with 1.9 and 2.1 defects per tree, respectively. Trees in the SBSvk had significantly more weevil attacks high on the bole than trees in the SBSwk.Key words: white pine weevil, Pissodes strobi, white spruce, Engelmann spruce, Picea engelmannii x P. glauca Les CpidCmies antkrieures du charangon du pin blanc, Pissodes strobi (Peck), ont Ct C reconstitukes par l'examen des arbres debout et abattus dans les peuplements de 1'intCrieur rkgknkrCs naturellement d'kpinettes dans la For2t modkle de McGregor. Les Cpidkmies ont Ct C retrouvCes tant dans les sous-zones biogCoclimatiques de 1'6pinette sub-borCale (SBS), que pour les sous-zones fraiches et humides (SBSwk) et fraiches et trks humides (SBSvk), illustrant que les CpidCmies frCquentes de charangon constituent un CvCnement nature1 qui date d'avant l'intervention humaine. Prks du tiers de toutes les tiges dCfectueuses des 32 arbres abattus ont Ctk identifikes cornme ayant Ct C attaquCes par le charangon. Dans les sous-zones SBSwk et SBSvk, 56,3 % et 81,3 % des arbres abattus contenaient des dCfauts provoquCs par le charangon, atteignant pour chaque sous-zone, 1,9 et 2,l dCfauts par arbre. Les arbres de la sous-zone SBSvk ont connu significativement plus d'attaques du charangon haut sur la tige que dans le cas des arbres de la sous-zone SBSwk.Mots-~16s: charangon du pin blanc, Pissodes strobi, Cpinette blanche, Cpinette d'Engelmann, Picea engelmannii x P. glauca

Geographic variation in resin canal defenses in seedlings from the Sitka spruce × white spruce introgression zone

“…Why pure Sitka and white spruce differ so greatly in resin canal traits is an interesting question. Historically, white spruce may have been subject to greater pest pressure generally or to stronger or more prolonged exposure to Pissodes strobi in particular, because of the high incidence of even-aged, fire-regenerated white spruce stands in the more continental interior regions, which favour weevil reproduction (Kimoto et al 2000). The introgression zone may have served as a hybrid bridge (Pilson 1999) to facilitate the spread of Pissodes strobi westward from white spruce to Sitka spruce in the relatively recent past.…”

Growth of interior spruce and attack by the white pine weevil, Pissodes strobi (Peck) in the sub-boreal spruce zone of British Columbia: Role of overstorey shade.

“…Infestations o f white pine weevil are known to have occurred after natural disturbance events such as wildfires (Kimoto et al 2000).…”

“…These practices are firstly, the . Clear-cuts may resemble burned areas which occur in the natural forest (Kimoto et al 2000). Such areas create conditions that allow weevil-populations to flourish because they have easy access to a large number o f host terminals, and temperatures are also elevated for brood development to levels which meet the required 785 degree-days above 7.2°C (McMullen 1976).…”