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BACILLUS THURINGIENSIS δ-ENDOTOXEV: ON THE RELATIVE ROLES OF SPORES AND CRYSTALS IN TOXICITY TO SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE)1

Published online by Cambridge University Press:  31 May 2012

P. G. Fast
P. G. Fast
Affiliation:
Insect Pathology Research Institute, Canadian Forestry Service, Sault Ste. Marie, Ontario P6A 5M7
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Abstract

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Newly moulted sixth instar larvae of spruce budworm, Choristoneura fumiferana, were force fed graded dosages of preparations containing (1) purified crystals, (2) purified spores, and (3) mg/mg mixtures of purified spores and purified crystals. The LD50 for purified crystals was 0.094 μg/larva and for the mixture 0.096 μg/larva but the latter preparation had an LD50 of 0.048 μg/larva based on crystals indicating that the presence of 2.4 × 105 spores enhanced the toxicity of crystals twofold. The LD50 spore crystal corresponded to LD60 for crystals alone. The LD50 for spores treated with proteinase to remove residual crystals was 20 μg/larva, or 1,0 × 108 spores. The regression coefficients were not significantly different from each other in all three preparations indicating a common or similar mode of action. It is concluded that spores play little or no role in mortality of spruce budworm induced by Bacillus thuringiensis insecticides.

Résumé

Des larves du sixième stade to Tordeuse des bourgeons de l’Epinette (Choristoneura fumiferana) de mue récente ont été gavées au moyen de préparations à doses calibrées contenant (1) des cristaux purifiés, (2) des spores purifiées et (3) des mélanges mg/mg de spores purifiées et de cristaux purifiés. En cristaux purifiés, le LD50 "titrait" à 0.094 μg/larve, et en mélange, à 0.096 μg/larve, mais cette dernière préparation avait une puissance réelle en LD50 de 0.048 μg/larve, vu que la présence de 2.4 × 105 spores rehaussait 2 fois la toxicité des cristaux. Le LD50 sporesxristaux correspondait à LD60 pour les cristaux seuls. Pour les spores purifiées, le LD50 correspondait à 20 μg/larve ou 1.0 × 108 spores. Les coefficients de régression ne furent pas significativement différents l’un de l’autre dans les trois préparations, indiquant un mode d’action commun ou similaire. L’auteur conclut que les spores jouent un rôle à peu près nul dans la mortalité de la Tordeuse des bourgeons de l’Epinette produite par des insecticides contenant Bacillus thuringiensis.

Type
Articles
Information
The Canadian Entomologist , Volume 109 , Issue 11 , November 1977 , pp. 1515 - 1518
Copyright
Copyright © Entomological Society of Canada 1977

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