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SUSCEPTIBILITY OF LARVAL INSTARS OF SPRUCE BUDWORM, CHORISTONEURA FUMIFERANA (LEPIDOPTERA: TORTRICIDAE), TO BACILLUS THURINGIENSIS

Published online by Cambridge University Press:  31 May 2012

Paul G. Fast  and
John B. Dimond
Paul G. Fast
Affiliation:
Forest Pest Management Institute, Canadian Forestry Service, Sault Ste. Marie, Ontario P6A 5M7
John B. Dimond
Affiliation:
Department of Entomology, University of Maine, Orono, Maine 04469
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Abstract

Diet incorporation assays detected no difference in susceptibility of instars IV, V, and VI of spruce budworm exposed to Bacillus thuringiensis, either in terms of dose, LC50, or time, LT50. The hypothesis that the dose–response for larvae of each instar fitted a common regression line was statistically acceptable. Differences in the pattern of changes in larval weight of instars IV, V, VI larvae in response to dose were not detected.

Small plots were sprayed with 5.5, 10.9, 21.9 BIU/ha at times corresponding to peak instar III, early IV, peak IV, peak V, and peak VI. Instar III larvae were controlled less effectively than were instar IV or V larvae which were controlled equally well. Instar VI larvae were also less effectively controlled than instar IV and V larvae probably because a significant proportion had reached the non-feeding prepupal stage before the full effect of B.t. was obtained.

Résumé

Aucune différence de vulnérabilité en fonction de la dose, CL50, et du temps, TL50, n'a été décelée chez des larves de la tordeuse des bourgeons de l'épinette du 4e au 6e stades soumises à un régime alimentaire contenant Bacillus thuringiensis. À l'analyse groupée des résultats obtenus pour chaque stade, l'hypothèse d'une droite commune de régression était statistiquement acceptable. On n'a pas décelé de différence dans l'évolution pondérale des larves en fonction de la dose.

Sur des parcelles traitées avec 5.5, 10.9 et 21.9 U.I./ha à divers moments correspondant au maximum du 3e stade, au début du 4e stade, au maximum du 4e, au maximum du 5e et au maximum du 6e, les larves du 3e stade ont été moins bien réprimées que celles des 4e et 5e stades. Même constat pour les larves du 6e stade, peut-être parce qu'une partie notable d'entre elles ont cessé de se nourir avant de métamorphoser aux chrysalides, avant que B.t. ne fasse complètement effet.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 2 , February 1984 , pp. 131 - 137
Copyright
Copyright © Entomological Society of Canada 1984

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