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WHITE SPRUCE AND THE SPRUCE BUDWORM: DEFINING THE PHENOLOGICAL WINDOW OF SUSCEPTIBILITY

Published online by Cambridge University Press:  31 May 2012

Robert K. Lawrence ,
William J. Mattson  and
Robert A. Haack
Robert K. Lawrence
Affiliation:
USDA Forest Service, North Central Forest Experiment Station, 1407 South Harrison Road, Room 220, East Lansing, Michigan, USA 48823
William J. Mattson
Affiliation:
USDA Forest Service, North Central Forest Experiment Station, 1407 South Harrison Road, Room 220, East Lansing, Michigan, USA 48823
Robert A. Haack
Affiliation:
USDA Forest Service, North Central Forest Experiment Station, 1407 South Harrison Road, Room 220, East Lansing, Michigan, USA 48823
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Abstract

Synchrony of insect and host tree phenologies has often been suggested as an important factor influencing the susceptibility of white spruce, Picea glauca (Moench) Voss, and other hosts to the spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae). We evaluated this hypothesis by caging several cohorts of spruce budworm larvae on three white spruce populations at different phenological stages of the host trees, and then comparing budworm performance with host phenology and variation of 13 foliar traits. The beginning of the phenological window of susceptibility in white spruce occurs several weeks prior to budbreak, and the end of the window is sharply defined by the end of shoot growth. Performance was high for the earliest budworm cohorts that we tested. These larvae began feeding 3–4 weeks prior to budbreak and completed their larval development prior to the end of shoot elongation. Optimal synchrony occurred when emergence preceded budbreak by about 2 weeks. Larval survival was greater than 60% for individuals starting development 1–3 weeks prior to budbreak, but decreased to less than 10% for those starting development 2 or more weeks after budbreak and thus completing development after shoot elongation ceased. High performance by the budworm was most strongly correlated with high levels of foliar nitrogen, phosphorous, potassium, copper, sugars, and water and low levels of foliar calcium, phenolics, and toughness. These results suggest that advancing the usual phenological window of white spruce (i.e. advancing budbreak prior to larval emergence) or retarding budworm phenology can have a large negative effect on the spruce budworm’s population dynamics.

Résumé

Le synchronisme de la phénologie d’un insecte et de celle de son hôte est souvent invoqué pour expliquer la sensibilité de l’épinette blanche, Picea glauca (Moench) Voss, et d’autres arbres hôtes à la Tordeuse des bourgeons de l’épinette, Choristoneura fumiferana (Clemens) (Lepidoptera : Tortricidae). Nous avons étudié la validité de cette hypothèse en encageant plusieurs cohortes de larves de la tordeuse sur trois populations d’épinettes blanches à divers stades phénologiques; nous avons ensuite observé la performance des tordeuses en fonction de la phénologie des hôtes et en fonction de 13 caractéristiques foliaires. Le début de la période de sensibilité de l’épinette se produit plusieurs semaines avant l’éclosion des bourgeons et la fin de la période arrive abruptement, à la fin de la croissance des rameaux. La performance s’est avérée très bonne chez les cohortes les plus hâtives de tordeuses que nous avons testées. Les larves ont commencé à se nourrir 3–4 semaines avant l’éclosion des bourgeons et avaient complété leur développement avant la fin de la croissance des rameaux. Le synchronisme était optimal lorsque l’émergence précédait l’éclosion des bourgeons d’environ 2 semaines. La survie des larves s’est avérée supérieure à 60% chez les individus qui ont commencé à se développer 1–3 semaines avant l’éclosion des bourgeons, mais a été estimée à moins de 10% chez les individus qui ont commencé à se développer 2 semaines ou plus après l’éclosion des bourgeons et qui ont donc complété leur développement après la période d’élongation des rameaux. La meilleure performance des tordeuses était en forte corrélation avec des concentrations foliaires élevées d’azote, de phosphore, de potassium, de cuivre, de sucres et d’eau, avec de faibles concentrations foliaires de calcium et de produits phénolés et avec une coriacité peu élevée. Ces résultats semblent indiquer que le déplacement de la fenêtre phénologique habituelle de l’épinette blanche pour qu’elle couvre une période plus précoce (par manipulation de la période d’éclosion des bourgeons de façon à ce qu’elle se produise avant l’émergence), ou le retard de la phénologie de la tordeuse pourraient avoir des effets négatifs importants sur la dynamique des populations de tordeuses.

[Traduit par la Rédaction]

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The Canadian Entomologist , Volume 129 , Issue 2 , April 1997 , pp. 291 - 318
Copyright
Copyright © Entomological Society of Canada 1997

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