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CLIMATE AND THE ECOLOGY OF THE BALSAM WOOLLY APHID

Published online by Cambridge University Press:  31 May 2012

D. O. Greenbank
Affiliation:
Forest Research Laboratory, Department of Fisheries and Forestry, Fredericton, New Brunswick

Abstract

The balsam woolly aphid was introduced over 60 years ago from Europe into the Maritime Provinces of Canada where it established on Abies balsamea (L.) Mill. Ecological characteristics of the insect that are important to the survival and spread of populations in the new environment are feeding habits, cold-hardiness, and dispersal capacity. The aphid feeds on the bark cortex of all parts of the tree from the stem to the crown. ’Stem attack’ refers to the population established on the main stem while ’twig attack’ refers to the population established in the crown where the aphid may settle on numerous sites but mainly at the base of young shoots. Freezing is fatal and the probability of freezing increases as temperatures fall below −5°F. There are no survivors at −35°F no matter how brief the exposure. The adults are wingless and populations are spread mainly through wind dispersal of crawlers and eggs.The climate of the Maritime Provinces changes markedly from the coast inland from maritime, through transitional, to continental. Infestations in maritime and continental climatic regions follow particular patterns while in the transitional region the course of infestation is irregular. Climate is unimportant in determining population trend in maritime climatic regions. The probability of experiencing temperatures below −15°F in a winter is 0.10 and populations survive on the stem and in the crown. Crown populations are dispersed freely and the aphid and aphid damage is general. In the continental climatic region, the probability of −30°F occurring in a winter is 0.46 and populations are restricted to the base of the tree where snow cover provides protection. Wind velocities below the canopy are light and infestations remain isolated and small with damage from stem attack accumulating at a slow rate. In the transitional climatic region, the severity of winter is irregular with periols of mild winters being broken by occasional extremely cold winters. Tree mortality from twig and stem attack has been heavy in some stands while infestations in adjacent and equally susceptible stands have been arrested by severe winters.

Résumé

Voilà plus de 60 ans que le Puceron lanigère du Sapin (Ade’ges piceae) introduit d’Europe s’est établi dans les Maritimes sur Abies balsamea (L). Mill. Les caractères écologiques qui lui permettent de survivre et de se propager en ce nouveau pays sont ses habitudes le nutrition, sa rusticité contre le froid, et sa capacité de dispersion. Il mange les tissus de l’écorce partout sur l’arbre. "L’attaque de tige" signifie la population installée sur la tige, "l’attaque de rameaux" la population un peu partout dans la cime mais surtout à la base des jeunes pousses. Il peur mourir de froid et depuis la tempérarure ambiante de −5°F, les possibilités qu’il gèle augmentent. Une exposition à −35°F, tant toit peu brève, tue tous les individus. L’adulte étant aptère, l’espèce se répand surtout avec les chenilles et les oeufs transportés par le vent.Le climat des Maritimes varie de continental à maritime selon que l’on s’éloigne ou pas des côtes. Dans chacune des deux régions, l’infestation a son propre type, tandis que dans la zone de transition, elle a un comportement irrégulier. Dans la région maritime, le climat n’influe pas sur les tendances de la population. Ainsi la probabilité que la température hibernale baisse en bas de −15°F n’étant que de 0.10, les Pucerons survivent bien sur la tige et dans la cime dans laquelle ils sont dispersés et qu’ils endommagent dans toutes ses parties. En region continentale, par contre, la probabilité que la tempérarure baisse à −30° F est de 0.46 et les survivants se rencontrent seulement à la base de l’arbre dans la neige. Sous la voûte foliacée, la faible vitesse du vent réduit l’étendue et la propagation des infestations et le taux de dommage aux tiges demeure bas. Dans la zone de transition, les hivers sont parfois doux, parfois très rigoureux; la mortalité des arbres attaqués s’élève beaucoup dans certains peuplements alors que dans les peuplements adjacents et aussi vulnérables, l’infestation s’arrête à cause du froid intense qui y sévit.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1970

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