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EFFECT OF TEMPERATURE AND EXPOSURE TIME ON TOXICITY OF BACILLUS THURINGIENSIS BERLINER SPRAY DEPOSITS TO SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA CLEMENS (LEPIDOPTERA: TORTRICIDAE)

Published online by Cambridge University Press:  31 May 2012

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

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Experiments were conducted using balsam fir twigs treated with Bacillus thuringiensis Berliner to examine the influence of temperature and exposure time on mortality of spruce budworm, Choristoneura fumiferana Clemens. Twigs were sprayed with a commercial formulation (8.4 BIU/L) using droplets of 40–70 μm diameter at densities, ranging from 0.5 to 5.5 droplets per needle. Temperature affected progression but not the level of cumulative mortality during 14 days of feeding on sprayed foliage. The LT50 decreased from 12–17 days at 13°C to 2–4 days at 25°C, depending on droplet density. Temperature between 13 and 25°C had a limited effect on dose acquisition because 40–60% of the larvae were able to acquire a lethal dose within 1 day of feeding on foliage with 0.5–1.5 droplets per needle, regardless of temperature. Under these conditions dose acquisition was not limited by temperature-dependent consumption of foliage, but rather by feeding inhibition associated with the dose initially ingested. This also limited the influence of exposure time; a 7- or 14-fold increase in exposure time increased larval mortality at most by 25%. Implications of these findings for improving efficacy of B. thuringiensis in forestry applications are discussed.

Résumé

Des expériences ont été menées utilisant des branches de sapin baumier traitées avec Bacillus thuringiensis Berliner afin d’étudier l’influence de la température et du temps d’exposition sur la mortalité de la tordeuse des bourgeons de l’épinette, Choristoneura fumiferana Clemens. Les branches ont été arrosées d’une formule commerciale (8,4 BIU/L) utilisant des gouttelettes de 40–70 μm de diamètre à des densités variant entre 0,5 et 5,5 gouttelettes par aiguille. Pendant 14 jours de nutrition sur du feuillage traité, la température a affecté la progression de la mortalité mais pas son niveau cumulatif. Le TL50 est passé de 12–17 jours à 13°C, à 2–4 jours à 25°C, dépendant de la densité des gouttelettes. La température entre 13 et 25°C n’a eu qu’un effet limité sur l’acquisition de dose puisque 40–60% des larves ont été capables d’ingérer une dose léthale à l’intérieur d’une journée de nutrition sur du feuillage avec 0.5–1.5 gouttelettes par aiguille, quelque soit la température. Sous ces conditions, l’acquisition de dose n’a pas été limitée par un niveau de consommation du feuillage dépendant de la température, mais plutôt par l’inhibition de la nutrition associée à la dose initiallement ingérée. Ceci a aussi limité l’influence du temps d’exposition; une augmentation du temps d’exposition par un facteur de 7 à 14 n’a augmenté la mortalité larvaire qu’au plus de 25%. Les implications de ces résultats pour l’amélioration de l’efficacité de B. thuringiensis en foresterie sont discutées.

Type
Articles
Information
The Canadian Entomologist , Volume 122 , Issue 1 , February 1990 , pp. 69 - 75
Copyright
Copyright © Entomological Society of Canada 1990

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