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  • L. C. Wright (a1), A. A. Berryman (a1) and B. E. Wickman (a1)

Fir engraver and Douglas-fir beetle numbers were monitored during and after an outbreak of the Douglas-fir tussock moth. The population behavior of the two species of bark beetles was similar. Number of emerged offspring/female was highest during the years of defoliation and declined afterward. Total number of beetle attacks peaked 1 to 2 years after defoliation ended and then declined. During and 1 year after defoliation, beetles generally infested trees that had greater than 90% defoliation. After this time infestations were not as strongly associated with heavily defoliated trees. Life tables were constructed for beetles within trees and for beetles per area of forest land. Key mortality factors acting on beetles within trees occurred during the larval and pupal stages. Mortality during adult dispersal was a key factor when beetle density per area of land was considered. Although beetle offspring emerging per dm2 of bark surface was relatively low in defoliated trees, defoliation appeared to reduce host resistance which enabled beetles to successfully attack at lower densities, reducing intraspecific competition, and resulting in increased emergence of offspring/female parent.

Le scolyte Scolytus ventralis et le dendroctone du Douglas, Dendroctonus pseudotsugae ont été suivis pendant et après une infestation de la chenille à houppes du Douglas. L'évolution des populations des deux coléoptères s'est avérée similaire. Le nombre de progénitures/femelle était maximal pendant les années de défoliaison et a baissé par la suite. Le nombre total d'attaques a atteint son sommet un à deux ans après l'arrêt de la défoliaison et a chuté ensuite. Pendant la défoliaison et jusqu'à un an après, les coléoptères ont généralement infesté des arbres défoliés à plus de 90%. Par après, les infestations n'étaient pas aussi clairement associées aux arbres sévèrement défoliés. Des tables de survie ont été préparées sur la base des nombres de coléoptères par arbre et par unité de surface du couvert forestier. Les facteurs-clés expliquant la mortalité intra-arbre ont agi pendant les stades larvaires et pupal. La mortalité durant la dispersion par le vol est apparue comme un facteur-clé lorsque la densité des coléoptères par unité de surface était considérée. Bien que le nombre de progénitures émergées par dm2 de surface de l'écorce était relativement basse pour les arbres défoliés, la défoliaison a semblé réduire la résistance de l'hôte ce qui a favorisé l'attaque à basse densité, réduisant ainsi la compétition intraspécifique et causant une augmentation du nombre de progénitures émergeant par femelle.

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The Canadian Entomologist
  • ISSN: 0008-347X
  • EISSN: 1918-3240
  • URL: /core/journals/canadian-entomologist
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