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PEST MANAGEMENT OF DOUGLAS-FIR TUSSOCK MOTH (LEPIDOPTERA: LYMANTRIIDAE): PREVENTION OF AN OUTBREAK THROUGH EARLY TREATMENT WITH A NUCLEAR POLYHEDROSIS VIRUS BY GROUND AND AERIAL APPLICATIONS

Published online by Cambridge University Press:  31 May 2012

R. F. Shepherd ,
I. S. Otvos ,
R. J. Chorney  and
J. C. Cunningham
R. F. Shepherd
Affiliation:
Canadian Forestry Service, Pacific Forest Research Centre, Victoria, British Columbia V8Z 1M5
I. S. Otvos
Affiliation:
Canadian Forestry Service, Pacific Forest Research Centre, Victoria, British Columbia V8Z 1M5
R. J. Chorney
Affiliation:
British Columbia Ministry of Forests, Kamloops, British Columbia V2C 2T7
J. C. Cunningham
Affiliation:
Canadian Forestry Service, Forest Pest Management Institute, Sault Ste. Marie, Ontario P6A 5M7
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Abstract

Two different application methods were tested using a nuclear polyhedrosis virus as a control agent at an early stage in the outbreak cycle of Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), in south central British Columbia in 1981. The virus, which often leads to the development of an epizootic late in the outbreak cycle, was propagated in whitemarked tussock moth, Orgyia leucostigma (J. E. Smith). A helicopter fitted with a boom and nozzle was used for treating four plots (total area 19.8 ha) at a dosage of 2.2 × 1011 polyhedral inclusion bodies (PIB) in an emitted volume of 11.3 L ha−1. Five to eight weeks after spraying, microscopic examination of live larvae showed that 77 to 100% were infected. In ground-spray applications of two other plots, a modified orchard-type sprayer was used to apply 2.4 × 1010 PIB in a volume of 4.5 L per tree. Microscopic diagnosis of live larvae at 8 weeks post-spray revealed 83 and 85% infection.In autumn 1981, no egg masses could be found in the plots treated earlier that year and no larvae were found on the sample trees in 1982 or 1983. The treatment was effective over a range of initial mean larval densities of 41 to 206 m−2 of foliage. At the same time, populations in nearby untreated areas increased in 1982. Little foliage protection was obtained the year of application due to the lengthy virus incubation period, but the trees recovered quickly when populations disappeared due to the virus epizootic.

Résumé

Deux techniques différentes d'épandage ont été employées avec un virus de la polyédrose nucléaire pour lutter contre la chenille à houppes du douglas, Orgyia pseudotsugata (McDunnough), au début de son cycle de pullulation dans le centre-sud de la Colombie-Britannique en 1981. Le virus, qui entraîne souvent une épizootie lorsqu'il est employé à un stade avancé du cycle, a été multiplié sur la chenille à houppes blanches, Orgyia leucostigma (J. E. Smith). Un hélicoptère équipé d'une rampe de gicleurs a été employé pour traiter quatre parcelles (superficie totale de 19.8 ha) à une dose de 2.2 × 1011 corps d'inclusion polyédriques (CIP) dans un volume à l'émission de 11.3 L ha−1. Cinq à huit semaines après l'arrosage, l'examen microscopique des larves vivantes a révélé que 77 à 100% d'entre elles étaient infectées. Deux autres parcelles ont été arrosées au sol à l'aide d'un pulvérisateur modifié (du type employé dans les vergers), chaque arbre recevant 2.4 × 1010 CIP dans 4.5 L. L'examen microscopique des larves vivantes huit semaines plus tard a indiqué des taux d'infection de 83 à 85%.À l'automne 1981, on n'a trouvé aucune masse d'oeufs dans les parcelles traitées plus tôt au cours de l'année et en 1982 et 1983 on n'a décelé aucune larve sur les arbres échantillons. Le traitement s'est révélé efficace pour un intervalle de densité moyenne initiale de 41 à 206 larves par mètre carré de feuillage. Par ailleurs, les populations dans les régions voisines non traitées avaient augmenté en 1982. Au cours de l'année d'épandage, la protection du feuillage a été faible en raison de la longue période d'incubation du virus, mais les arbres se sont rétablis rapidement lorsque les populations ont disparu sous l'effet de l'épizootie virale.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 11 , November 1984 , pp. 1533 - 1542
Copyright
Copyright © Entomological Society of Canada 1984

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