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THE INFLUENCE OF PARASITISM BY APANTELES FUMIFERANAE VIER. (HYMENOPTERA: BRACONIDAE) ON SPRING DISPERSAL AND CHANGES IN THE DISTRIBUTION OF LARVAE OF THE SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE)

Published online by Cambridge University Press:  31 May 2012

Vincent Nealis  and
Jacques Régnière
Vincent Nealis
Affiliation:
Canadian Forestry Service, Great Lakes Forestry Centre, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
Jacques Régnière
Affiliation:
Canadian Forestry Service, Great Lakes Forestry Centre, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
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Abstract

Most emerging 2nd-instar larvae of spruce budworm, Choristoneura fumiferana (Clem.), tested in the laboratory were photopositive and there was no difference in response between healthy larvae and larvae parasitized by Apanteles fumiferanae Vier. However, in the field, parasitized individuals were under-represented among larvae dispersing on silk threads between tree crowns. There is evidence that this was due to the relatively late emergence of parasitized larvae. These parasitized larvae therefore encountered fewer crawling larvae at the tips of branches, and consequently their propensity for dispersing was reduced.

The vertical distribution of dispersing, parasitized larvae caught on sticky traps more closely resembled that of established larvae than it did the vertical distribution of the overwintering population. This indicates that there was some differential redistribution of parasitized and nonparasitized individuals. Despite these differences, the estimate of parasitism by A. fumiferanae based on mid-crown branch samples is justified because it is most consistent and most closely reflects the overall frequency of parasitism.

Résumé

La plupart des larves émergeantes de la tordeuse des bourgeons de l’épinette, Choristoneura fumiferana (Clem.), testées en laboratoire étaient photopositives, et nous n’avons trouvé aucune différence de réponse entre les larves saines et celles parasitées par Apanteles fumiferanae Vier. Toutefois, sur le terrain, les individus parasités étaient sous-représentés parmi les larves se dispersant sur un fil de soie entre les couronnes des arbres. Certaines données suggèrent que ceci serait causé par l’émergence relativement tardive des larves parasitées. Ces mêmes larves rencontreraient moins de larves rampant à l’extrémité des branches, ce qui les porterait moins à se disperser.

La distribution verticale du taux de parasitisme dans les larves en dispersion capturées sur des pièges collants se rapproche davantage de celle dans les larves établies que de celle dans les larves en hibernation, ce qui indique une redistribution différentielle, dans la couronne, des individus parasités et non-parasités. En dépit de ces différences, un estimé du taux de parasitisme par A. fumiferanae obtenu à partir d’un échantillon prélevé à la mi-couronne est justifié puisque c’est là que ce taux est le plus consistant et qu’il reflète le plus étroitement le taux global.

Type
Articles
Information
The Canadian Entomologist , Volume 119 , Issue 2 , February 1987 , pp. 141 - 146
Copyright
Copyright © Entomological Society of Canada 1987

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