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AERIAL APPLICATION OF NUCLEAR POLYHEDROSIS VIRUS AGAINST DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (McDUNNOUGH) (LEPIDOPTERA: LYMANTRIIDAE): II. IMPACT 1 AND 2 YEARS AFTER APPLICATION

Published online by Cambridge University Press:  31 May 2012

I.S. Otvos ,
J.C. Cunningham  and
R.I. Alfaro
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
R.I. Alfaro
Affiliation:
Canadian Forestry Service, Pacific Forestry Centre, Victoria, British Columbia, Canada V8Z 1M5
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Abstract

Following aerial application of a Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough), nuclear polyhedrosis virus (NPV) product called Virtuss on four plots in 1982, observations were made to determine the impact of these treatments in 1983 and 1984. Treated plots as well as buffer zones between and adjoining the treated plots, and three of the four check plots established in 1982, were monitored. The NPV appeared to have spread from the treated plots to adjoining areas in 1982, effectively reducing the Douglas-fir tussock moth population. This observation suggests that a strategy of spraying alternate swaths of Douglas-fir tussock moth infested stands with this viral insecticide may effectively initiate an epizootic that would control the population at a reduced cost.

A naturally occurring NPV epizootic decimated the Douglas-fir tussock moth population in the three check plots in 1983, but severe tree mortality occurred in two of these plots with 60 and 62% of sample trees dead in 1984. Light tree mortality was noted in 1984 in two of the four treated plots with 4 and 7% of sample trees killed. It is concluded that the virus treatments in 1982 were successful in preventing tree mortality.

Résumé

Un épandage aérien d’un produit appelé Virtuss et contenant le virus de la polyédrose nucléaire (VPN) de la chenille à houppes du douglas, Orgyia pseudotsugata (McDunnough), a été effectué sur quatre placettes en 1982. En 1983 et 1984, on a cherché à déterminer les répercussions de ces traitements dans les placettes traitées de même que dans les zones tampons de chaque côté des placettes et on a aussi examiné trois des quatre placettes témoins établies en 1982. Il semblerait que le VPN se soit propagé aux zones voisines où une nette réduction de la population de la chenille a été observée. On peut donc penser qu’une stratégie consistant à alterner les bandes arrosées et non arrosées dans les peuplements infestés pourrait être efficace en déclenchant une épizootie qui permettrait de réduire la population à un coût réduit.

Une épizootie du VPN d’origine naturelle a décimé la population de la chenille dans les trois placettes témoins en 1983; on a cependant observé en 1984 une mortalité très importante des arbres dans deux de ces placettes, soit de 60 et 62% des arbres d’échantillonnage. Par contre, une faible mortalité des arbres a été observée en 1984 dans deux des placettes traitées où 4 et 7% des arbres d’échantillonnage avaient été tués. On en conclut que les traitements viraux appliqués en 1982 ont permis d’empêcher une mortalité élevée des arbres.

Type
Articles
Information
The Canadian Entomologist , Volume 119 , Issue 7-8 , August 1987 , pp. 707 - 715
Copyright
Copyright © Entomological Society of Canada 1987

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