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MORTALITY, FEEDING INHIBITION, AND RECOVERY OF SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE) LARVAE FOLLOWING AERIAL APPLICATION OF A HIGH-POTENCY FORMULATION OF BACILLUS THURINGIENSIS SUBSP. KURSTAKI

Published online by Cambridge University Press:  31 May 2012

Kees van Frankenhuyzen ,
Carl Nystrom ,
John Dedes  and
Vern Seligy
Kees van Frankenhuyzen*
Affiliation:
Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, P.O. Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
Carl Nystrom
Affiliation:
Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, P.O. Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
John Dedes
Affiliation:
Great Lakes Forestry Centre, Canadian Forest Service, Natural Resources Canada, P.O. Box 490, Sault Ste. Marie, Ontario, Canada P6A 5M7
Vern Seligy
Affiliation:
Environmental and Occupational Toxicology Division, Environmental Health Centre, Health Canada, Tunney's Pasture, Ottawa, Ontario, Canada K1A 0L2
*
1 Author to whom all correspondence should be addressed (E-mail: [email protected]).
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Abstract

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A larval population of spruce budworm, Choristoneura fumiferana (Clemens), was monitored for 5 d following aerial application of a commercial formulation of Bacillus thuringiensis Berliner subsp. kurstaki to investigate dose acquisition and expression (larval mortality, recovery, feeding, and growth) in relation to spray deposition and persistence of spray deposits. The main objective was to test if previous laboratory observations on how B. thuringiensis affects feeding and dose ingestion by spruce budworm larvae hold true under field conditions. About 40% of the treated population ingested a lethal dose within 1 d after spray application. Lethally dosed larvae died without further feeding upon transfer from treated foliage to (untreated) artificial diet. Resumption of feeding by larvae that survived the treatment was delayed relative to larvae from the control population during 3 d following spray application; during that time, normal feeding activity and larval weight gain were suppressed. Inhibited feeding by survivors appeared to prevent further dose uptake because the proportion of lethally dosed larvae in daily collections did not increase despite significant residual spray deposits in budworm feeding sites. Restoration of "normal" recovery times by the fourth day coincided with a 65–85% reduction in persistence of the pathogen on the foliage and did not result in further lethal dose acquisition, as treatment-induced mortality dropped to about 20% on the 4th and 5th days. The observations are consistent with previous laboratory observations of how B. thuringiensis affects larval feeding and with the hypothesis that feeding inhibition may be a limiting factor in the acquisition of a lethal dose.

Résumé

Une population de larves de la Tordeuse des bourgeons de l’épinette, Choristoneura fumiferana (Clemens), a été suivie pendant 5 jours après arrosage d’une préparation commerciale de Bacillus thuringienesis Berliner ssp. kurstaki afin de déterminer la fraction de la dose qui a été absorbée et ses effets (mortalité, récupération, alimentation et croissance) en relation avec la quantité de la préparation qui s’est déposée au sol et la persistance de ces résidus. Le but ultime de l’exercice était de vérifier si les observations antérieures en laboratoire des effets de B. thuringiensis sur l’alimentation et sur l’ingestion du bacille se produisent aussi sur le terrain. Environ 40% des larves traitées ont ingéré une dose létale en moins d’une journée. Les larves qui ont ingurgité une dose létale ont été transférées du feuillage traité à un régime artificiel (non traité) mais elles sont mortes sans chercher à se nourrir de nouveau. Le retour à l’alimentation chez les larves qui ont survécu au traitement s’est fait tardivement par rapport à la population témoin durant les 3 jours qui ont suivi l’arrosage; pendant ce temps, l’activité alimentaire normale et l’augmentation de la masse étaient inhibées. L’alimentation ainsi inhibée chez les larves survivantes semble les avoir empêchées d’ingurgiter davantage du produit puisque la proportion de larves tuées n’a pas augmenté dans les récoles quotidiennes, en dépit de la présence de résidus importants du produit aux sites d’alimentation des larves. Le retour à un temps « normal » de récupération le 4e jour coïncidait avec une réduction de 65–85% de la persistance du pathogène sur le feuillage et nous n’avons pas observé de nouvelle phase d’absorption létale à partir du moment ou la mortalité reliée au traitement est baissée à environ 20% le 4e et le 5e jours. Ces observations sont comparables aux résultat obtenus en laboratoire sur les effets de B. thuringiensis sur l’alimentation des larves et sont conformes à l’hypothèse selon laquelle l’inhibition de l’alimentation peut empêcher l’absorption d’une dose létale.

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 132 , Issue 4 , August 2000 , pp. 505 - 518
Copyright
Copyright © Entomological Society of Canada 2000

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