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EFFECT OF TEMPERATURE ON MORTALITY AND RECOVERY OF SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) EXPOSED TO BACILLUS THURINGIENSIS BERLINER

Published online by Cambridge University Press:  31 May 2012

Kees van Frankenhuyzen
Affiliation:
Forest Pest Management Institute, Canadian Forestry Service, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
Carl W. Nystrom
Affiliation:
Forest Pest Management Institute, Canadian Forestry Service, PO Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7

Abstract

Spruce budworm larvae were bioassayed against Bacillus thuringiensis Berliner to study the effect of temperature on the expression of toxicity. Temperatures between 16 and 28°C did not affect the ultimate level of toxicity (LC50). However, LT50’s increased from 2–8 days at 28°C to 11–20 days at 16°C, depending on concentration of the pathogen. When larvae were force-fed with a single dose, temperature had a similar effect on the time course of mortality without affecting the level of mortality. Feeding inhibition of force-fed larvae commenced immediately after dosing. Larvae that did not recover died without further feeding, even at lower temperatures when death occurred 2–3 weeks after dosing. Recovering larvae resumed feeding after 2 (28°C) to 6 (13°C) days. Recovered larvae took longer to develop and produced lighter pupae than untreated larvae. Our data suggest that temperature-dependent feeding and recovery did not contribute to quicker death at higher temperatures. Expression of the toxin itself appears to depend on temperature, possibly through the influence of temperature on metabolic rate of affected gut cells. Implications of these findings for the efficacy of spruce budworm control operations are discussed.

Résumé

On a étudié l’effet de la température sur l’expression de la toxicité du Bacillus thuringiensis Berliner à rencontre des larves de la tordeuse des bourgeons de l’épinette. Entre 16 et 28°C, la température n’a pas affecté le niveau ultime de toxicité (LC50). Cependant les LT50 ont augmenté de 2–8 jours à 28°C, jusqu’à 11–20 jours à 16°C, selon la concentration du pathogène. Lorsque les larves ont été forcées d’ingérer une dose unique, la température a eu un effet similaire sur la chronologie de la mortalité, sans affecter son niveau. L’arrêt de l’alimentation chez les larves forcées d’ingérer le produit est apparu dès après le traitement. Les larves qui n’ont pu récupérer sont mortes sans reprendre de nourriture, même aux basses températures alors que la mort ne survenait que 2–3 semaines après la traitement. Les larves qui ont récupéré ont recommencé à s’alimenter après 2 (28°C) à 6 jours (13°C). Les larves ayant récupéré ont mis plus de temps à se développer et ont produit des pupes plus petites que les larves non traitées. Nos données indiquent que la thermo-dépendance de l’alimentaiton et de la récupération ne contribuent pas à la mortalité accélérée observée à haute température. C’est l’expression même de la toxine qui semble dépendre de la température, possiblement via l’effect de celle-ci sur le taux métabolique des cellules entériques affectées. On discute des implications de ces observations pour les opérations de lutte contre la tordeuse.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1987

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