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MEAN WEIGHT AND REARING PERFORMANCE OF SUCCESSIVE EGG CLUSTERS OF EASTERN SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE)

Published online by Cambridge University Press:  31 May 2012

G. T. Harvey
G. T. Harvey
Affiliation:
Great Lakes Forest Research Centre, Canadian Forestry Service, Sault Ste. Marie, Ontario
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Abstract

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Detailed laboratory studies of mated spruce budworm (Choristoneura fumiferana (Clem.)) show that the number of eggs per day, mean cluster size, and mean wet weight of the eggs gradually decrease during the period of oviposition of individual moths. The term mean weight of initial eggs (Ei) is defined and compared with other measurements of mean egg weight based on total egg complement or parts of it. Ei is 6%–12% greater than the mean egg weight based on all eggs laid. In spite of variation in pattern of egg weight distribution among moths, Ei appears to express satisfactorily the differences in mean egg weight among moths and can be used to survey egg weights among populations.

Laboratory rearing studies of individual clusters indicate slightly slower emergence rates (seconds from hibernacula), greater survival, and smaller proportions of male pupae in the third and fourth quartiles of the egg complement; there were no differences in pupal weights related to cluster order. There is no ready explanation for this improved survival of larvae from eggs known to be smaller.

Implications of these results for the population dynamics of the spruce budworm are discussed. The more stressful conditions encountered in the natural environment may counteract the apparently better survival of individuals from the latter part of the egg complement.

Résumé

Des études détaillées de laboratoire sur les Tordeuses des bourgeons de l’Épinette (Choristoneura fumiferana [Clem.]) accouplées, indiquent que le nombre d’oeufs par jour, la grosseur moyenne des groupes, et la moyenne de poids mouillé des oeufs diminuent graduellement au cours de la période de ponte des papillons individuels. Le terme poids moyen des oeufs initiales (Ei) est défini et comparé aux autres mesurages de moyenne de poids des oeufs fondée sur la completion totale des oeufs ou sur des parties de celle-ci. Ei est de 6% à 12% plus grand que la moyenne du poids des oeufs fondée sur tous les oeufs pondus. Malgré la variation observée dans le mode de distribution du poids des oeufs chez les papillons, Ei semble exprimer d’une manière satisfaisante les différences de poids moyen des oeufs chez les papillons et peut aux études de poids des oeufs parmi les populations.

Des études sur l’élevage en laboratoire de groupes particuliers montrent des taux d’éclosion légèrent plus lents (en secondes par hibernacle) une meilleure survie et des proportions plus petites de pupes mâles pendant les troisième et quatrième quartils de complétion des oeufs; il n’y avait pas de différences de poids chez les pupes, par rapport aux groupes. Il n’existe aucune explication toute faite quant à l’amélioration de la survie chez les larves provenant d’oeufs reconnus plus petits.

L’auteur disserte sur les implications de ces résultats sur le dynamique des populations de Tordeuses des bourgeons de l’Épinette. Les conditions les plus contraignantes observées dans l’environnement naturel peuvent neutraliser l’apparente meilleure survie des sujets individuels de la dernière phase de complétion des oeufs.

Type
Articles
Information
The Canadian Entomologist , Volume 109 , Issue 4 , April 1977 , pp. 487 - 496
Copyright
Copyright © Entomological Society of Canada 1977

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