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COMPETITION AND POPULATION QUALITY IN DENDROCTONUS RUFIPENNIS (COLEOPTERA: SCOLYTIDAE)

  • A. J. Thomson (a1) and T. S. Sahota (a1)

Abstract

Spruce beetles (D. rufipennis) from a population homogeneous with respect to population quality were subjected to different degrees of competition at corresponding stages of their reproductive cycles by varying the spacing of individuals and by varying the time of introduction of individuals into the competitive environment. Competition effects increase with gallery accumulation, as suggested in previous studies, and result in subsequent reduction of gallery production and oviposition. Increase in individual beetle quality, however, confers increased powers of resistance to the competition effects. Initial egg-free length is an unsuitable attribute for comparisons of populations. Expression of reproductive efficiency is a dynamic population characteristic which varies over the reproductive cycle, and which may be readily estimated by measurement of yolk deposition rate. For comparing populations, such measurements would be more valuable when carried out before the onset of competition effects. Individuals with the highest quality at the start of the egg-production cycle exhibit the highest reproductive efficiency as conditions change.

Des dendroctones de l’épinette (D. rufipennis) d’une population homogène quant à la qualité des populations ont été assujetties à divers degrés de concurrence à des étapes correspondantes de leur cycle dé reproduction en variant l’espacement des sujets et le temps d’introduction dans ce milieu concurrentiel. Les effets de la concurrence augmentent au rythme de l’accumulation des galeries, tel que suggéré par des études antérieures et résultant en une diminution subséquente de la production de galeries et de la ponte. Toutefois, plus la qualité de chaque insecte augmente, plus s’accroissent les pouvoirs de résistance aux effets de la concurrence. La durée initiale sans œufs constitue une caractéristique inadéquate pour comparer les populations. L’expression de la capacité de reproduction constitue une caractéristique des populations dynamiques, qui varie selon le cycle de reproduction et qui peut être facilement évaluée en mesurant la vitesse de dépôt des jaunes.Aux fins de comparaison des populations, de tels mesurages seraient plus valables si effectués avant le début des effets de la concurrence. Les sujets dont la qualité est la meilleure au début du cycle de production d’œufs accusent la capacité de reproduction la plus élevée à mesure que les conditions changent.

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References

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Sahota, T. S. and Thomson, A. J.. 1979. Temperature induced variation in the rates of reproductive processes in Dendroctonus rufipennis (Coleoptera: Scolytidae): A new approach to detecting changes in population quality. Can. Ent. 111: 10691078.
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COMPETITION AND POPULATION QUALITY IN DENDROCTONUS RUFIPENNIS (COLEOPTERA: SCOLYTIDAE)

  • A. J. Thomson (a1) and T. S. Sahota (a1)

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