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AERIAL APPLICATION OF TWO BACULOVIRUSES AGAINST THE WESTERN SPRUCE BUDWORM, CHORISTONEURA OCCIDENTALIS FREEMAN (LEPIDOPTERA: TORTRICIDAE), IN BRITISH COLUMBIA

Published online by Cambridge University Press:  31 May 2012

I.S. Otvos
Affiliation:
Canadian Forestry Service, Pacific Forestry Centre, Victoria, British Columbia, Canada V8Z 1M5
J.C. Cunningham
Affiliation:
Canadian Forestry Service, Forest Pest Management Institute, Sault Ste. Marie, Ontario, Canada P6A 5M7
W.J. Kaupp
Affiliation:
Canadian Forestry Service, Forest Pest Management Institute, Sault Ste. Marie, Ontario, Canada P6A 5M7

Abstract

Two viruses, one a nuclear polyhedrosis virus and the other a granulosis virus, were applied in an attempt to initiate epizootics in populations of western spruce budworm, Choristoneura occidentalis Freeman, on Douglas-fir trees, Pseudotsuga menziesii (Mirb.) Franco, in southeastern British Columbia. Two 172-ha plots were aerially treated in 1982 with 9.0 kg of lyophilized, virus-infected larval powder that was formulated in an emulsifiable oil tank mix and applied at 9.4 L per hectare. Each plot was treated when larval populations were at the peak of the fourth instar. The nuclear polyhedrosis virus was applied at 5.4 × 1011 polyhedral inclusion bodies per hectare and the granulosis virus at 1.7 × 1014 capsules per hectare. Results showed that the granulosis virus treatment caused 34.6% population reduction (Abbott’s formula) and the nuclear polyhedrosis virus 51.8%. Larvae from treated and check plots were reared individually in the laboratory and the incidence of viruses, parasitoids, and successful adult emergence was recorded. Studies m these plots continued in 1983 and 1984. Although vertical transmission of both viruses was evident, their impact on budworm mortality was less than in 1982. Consequently, the epizootics were not sufficiently intense to control the target insect population.

Résumé

Deux virus, un virus à polyhédrose nucléaire et un virus à granulose, ont été appliqués lors d’une tentative de déclenchement d’épizooties dans les populations de la tordeuse occidentale de l’épinette, Choristoneura occidentalis Freeman, sur le sapin Douglas, Pseudotsuga menziesii (Mirb.) Franco, au sud est de la Colombie Britannique. Deux parcelles de 172 ha ont été traités par air en 1982 avec 9,0 kg de larves infectées, pulvérisées et formulées en huile émulsifiable appliquée à 9,4 L par hectare. Chaque parcelle a été traitée lorsque les populations larvaires étaient au pic de stade quatre. Le virus à polyhédrose nucléaire a été appliqué à 5,4 × 1011 corps d’inclusion polyhédriques par hectare et le virus à grandulose à 1,7 × 1011 capsules par hectare. Les résultats ont montré que le traitement au virus à granulose a causé 34,6% de réduction de la population (formule d’Abbott), et le virus à polyhédrose nucléaire, 51,8%. Des larves des parcelles traitées et témoins ont été élevées individuellement au laboratoire pour estimer les incidences de maladie virale, de parasitisme ou d’émergence d’un adulte. Les études dans ces parcelles se sont poursuivies en 1983 et 1984. Quoiqu’il ait été possible de conclure à la transmission verticale des deux virus, leur impact sur la mortalité de la tordeuse était moindre qu’en 1982. En conséquence, les épizooties n’étaient pas suffisamment intenses pour réprimer la population ciblée.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1989

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