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CONFIRMATIONS EXPERIMENTALES DU POTENTIEL DU COMPLEXE BACILLUS THURINGIENSIS ET CHITINASE POUR LA REPRESSION DE LA TORDEUSE DES BOURGEONS DE L’EPINETTE, CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE)

Published online by Cambridge University Press:  31 May 2012

W.A. Smirnoff
W.A. Smirnoff
Affiliation:
Centre de Recherches forestières des Laurentides, Service canadien des Forêts, Sainte-Foy, Québec
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Abstract

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Intensive and systematic laboratory studies conducted under various experimental conditions (larval stage, physiological condition of the insect, temperature, formulation) revealed that non-crystalliferous strains of Bacillus thuringiensis Berliner and B. cereus Frankland and Frankland were equally pathogenic for larvae of Choristoneura fumiferana Clemens as the crystalliferous strain of B. thuringiensis tested. Also the addition of minute quantities of chitinase (10,000 UN/ha) considerably increased the efficiency of commercial preparation of B. thuringiensis against C. fumiferana.

At 20°C, B. thuringiensis var. kurstaki provoked a slow septicemia in 3rd instar larvae of C. fumiferana which resulted in 90% larval mortality in 27 days. Under the same experimental conditions, a non-crystalliferous strain of B. thuringiensis (No. 17) and two strains of B. cereus, entomopathogens isolated from C. fumiferana and from a Tachinidae, also caused a slow septicemia resulting in 90% mortality of 3rd instar larvae after 30 to 32 days.

Experiments revealed that the symptoms of infection (lethargy, loss of weight) caused by B. thuringiensis + chitinase were far more rapid and pronounced than those provoked by B. thuringiensis alone The commercial preparation 26B prepared by Sandoz-Wander, applied at a rate of 16.8 × 109 BIU/ha caused only 80% mortality of 3rd and 4th stage larvae, while the complex Sandoz + chitinase N.B.C. provoked 100% larval mortality between 9 and 27 days depending upon the experimental conditions used Similar results were obtained with Dipel 36B. For instance, at 20°C Dipel + chitinase N.B.C. provoked 100% mortality of 3rd stage larvae in 9 days, while with Dipel alone, the same level of mortality was reached after 24 days. Also, it was established that C. fumiferana larvae reared on Abies balsamea were far more susceptible to the action of the bacillus than those reared on artificial diet.

These results confirmed that addition of chitinase considerably increased the pathogenic properties of B. thuringiensis on C. fumiferana and the low efficiency of the bacillus alone. The addition of chitinase to commercial B. thuringiensis preparations is required and of prime importance in future use of B. thuringiensis for the control of this insect pest.

Résumé

Des études intensives et systématiques qui ont été conduites en laboratoire en tenant compte de l’âge et de l’état physiologique de l’insecte, ainsi que des conditions de température, ont démontré que Bacillus thuringiensis Berliner non cristallogène ainsi que Bacillus cereus Frankland et Frankland étaient aussi pathogènes pour les larves de Choristoneura fumiferana Clemens que la souche de B. thuringiensis cristallogène testé. Ainsi, à 20°C, B. thuringiensis var. kurstaki provoquait chez les larves de 3e âge de C. fumiferana une lente septicémie causant la mortalité de 90% des larves en 27 jours. Dans des conditions expérimentales identiques, une souche de B. thuringiensis non cristallogène (n° 17) et deux souches de B. cereus entomopathogènes isolées chez C. fumiferana et chez un tachinidé causaient également une lente septicémie chez C. fumiferana et provoquaient 90% de mortalité des larves de 3e âge après une période de 30 à 32 jours.

Les expériences ont démontré par ailleurs que l’addition de quantités minimes de chitinase, soit l’équivalent de 10,000 UN/ha augmentait considérablement l’efficacité des préparations commerciales de B. thuringiensis contre C. fumiferana. Ainsi, la préparation bacillaire Sandoz-Wander (E.U.) 26B, dispersée à raison de 16.8 × 109 IU/ha, n’entraînait pas plus de 80% de mortalité des larves de 3e et de 4e âges après 30 jours, tandis que, avec l’addition de chitinase N.B.C., la mortalité était de 100% entre 9 et 27 jours selon les conditions expérimentales. Des résultats similaires ont été obtenus avec la préparation Dipel 36B; un taux de 100% de mortalité chez les larves de 3e âge a été atteint en 9 jours avec l’addition de chitinase et en 24 jours sans l’apport de cet enzyme. Dans un programme de lutte contre C. fumiferana à l’aide de B. thuringiensis, l’addition de chitinase s’avère donc essentielle.

Type
Articles
Information
The Canadian Entomologist , Volume 109 , Issue 3 , March 1977 , pp. 351 - 358
Copyright
Copyright © Entomological Society of Canada 1977

References

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