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FORECASTING THE EFFICACY OF OPERATIONAL BACILLUS THURINGIENSIS BERLINER APPLICATIONS AGAINST SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA CLEMENS (LEPIDOPTERA: TORTRICIDAE), USING DOSE INGESTION DATA: INITIAL MODELS

Published online by Cambridge University Press:  31 May 2012

Richard A. Fleming  and
Kees van Frankenhuyzen
Richard A. Fleming
Affiliation:
Forest Pest Management Institute, Forestry Canada, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
Kees van Frankenhuyzen
Affiliation:
Forest Pest Management Institute, Forestry Canada, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
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Abstract

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Single aerial applications of Bacillus thuringiensis Berliner (Bt) to control infestations of the eastern spruce budworm (Choristoneura fumiferana Clemens) have had varied operational success. Double applications are too expensive for general use, but might prove useful if directed to areas where the initial application was unsuccessful. This requires forecasts of the efficacy of the initial application in operational spray blocks within 4–5 days.

Data were collected in 30 spray blocks in 1989 in a feasibility study to determine if such forecasts of spray efficacy could be made from the prespray budworm population density, N0, and from the proportion of the population that had ingested a lethal dose Bt within 2 days of application, M. A mathematical model forecasting the postspray budworm population density, NF, was derived from population-dynamic considerations and fitted (r2 = 0.48, p < 0.0001):

The proportion of current foliage defoliated, D, depended (r = 0.81) on N0 and on whether the block was sprayed (I = 0) or not (I = 1):

Only one measure of defoliation involved M in any statistically significant way. The predicted (from values of N0) proportion of defoliation prevented by Bt application, dD, was weakly (r2 = 0.25, p = 0.002) related to M:

The large proportion of the variation in efficacy that remains unexplained by the models involving M limits the operational utility of this approach as it now stands for specific sites. The potential for further development of these models as decision support tools for fairly large spray blocks is discussed in terms of improving the sampling plan and including additional predictor variables.

Methods are also presented that reduce bias in calculations of population reduction (Abbott 1925) and foliage protection when data are available from few control and many treatment blocks.

Résumé

Les arrosages aériens uniques du bacille Bacillus thuringiensis Berliner (Bt) en vue de contenir les infestations de la Tordeuse des bourgeons de l’épinette (Choristoneura fumiferana Clemens) ont des taux de succès très variés. Les traitements doubles sont trop coûteux pour être employés couramment, mais pourraient être utiles dans des régions où le premier traitement s’est avéré inefficace. Il faudrait dans ce cas pouvoir préévaluer l’efficacité du traitement initial durant 4–5 jours dans des carrés d’arrosage spécifiques.

Des données ont été recueillies en 1989 dans 30 carrés d’arrosage au cours d’une étude de faisabilité, dans le but de déterminer si l’efficacité de l’arrosage pouvait être préévaluée en fonction de la densité initiale de la population de tordeuses avant l’arrosage, N0, et en fonction de la proportion de la population qui avait consommé une dose létale de Bt en moins de 2 jours après le traitement, M. Un modèle mathématique permettant de prédire la densité de la population de tordeuses après l’arrosage, NF, a été élaboré à partir de considérations démographiques et adjusté (r2 = 0.48, p < 0,0001):

La proportion de feuillage présent défolié, D, était fonction (r2 = 0,81) de N0, et variait selon que le carré avait été traité (I = 0) ou non (I = 1) :

Une seule mesure de la défoliation était fonction de M de façon statistiquement significative. La proportion prédite (à partir des valeurs de N0) de défoliation empêchée par l’application du bacille, dD, n’était que faiblement (r2 = 0,25, p = 0,002) reliée à M:

La proportion importante de la variation dans l’efficacité qui reste inexpliquée selon les modèles basés sur M limite l’utilité opérationnelle de cette approche comme elle existe actuellement dans le cas de sites spécifiques. La possibilité d’élargir ces modèles pour pouvoir les utiliser dans la planification de l’arrosage de carrés de grande taille est examinée en vue de l’amélioration du plan d’échantillonnage et de l’utilisation de variables additionnelles de prévision.

D’autres méthodes permettant de réduire le biais dans le calcul de la réduction de la population (Abbott 1925) et de la protection du feuillage sont examinées dans les cas où il y a peu de carrés témoins et plusieurs carrés traités.

[Traduit par la rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 124 , Issue 6 , December 1992 , pp. 1101 - 1113
Copyright
Copyright © Entomological Society of Canada 1992

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