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AERIAL APPLICATION OF NUCLEAR POLYHEDROSIS VIRUS AGAINST DOUGLAS-FIR TUSSOCK MOTH, ORGYIA PSEUDOTSUGATA (McDUNNOUGH) (LEPIDOPTERA: LYMANTRIIDAE): I. IMPACT IN THE YEAR OF APPLICATION

Published online by Cambridge University Press:  31 May 2012

I.S. Otvos ,
J.C. Cunningham  and
L.M. Friskie
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
L.M. Friskie
Affiliation:
British Columbia Ministry of Forests, Kamloops, British Columbia, Canada V2C 2T7
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Abstract

Four 10-ha plots located in Kamloops Forest District, British Columbia, containing Douglas-fir trees infested with Douglas-fir tussock moth were aerially sprayed with nuclear polyhedrosis virus (Virtuss) in 1982 when most larvae were in the first instar. A dosage of 2.5 × 1011 polyhedral inclusion bodies (PIB) per hectare was applied in an emulsifiable oil tank mix to one plot and the same dosage in an aqueous tank mix containing molasses was applied to a second plot. The remaining two plots were treated with dosages of 8.3 × 1010 and 1.6 × 1010 PIB per hectare, respectively, in the oil mix. The treatments were applied with a fixed-wing aircraft fitted with boom and nozzle equipment and calibrated to deliver 9.4 L/ha. A further four plots were selected as checks.

Population reduction at 6 weeks post-spray (calculated using a modified Abbott’s formula) was 65% in the plot receiving the lowest dosage and from 87 to 95% in the remaining three plots. Incidence of virus infection, determined microscopically, peaked at 5–6 weeks post-spray with 85–100% of the larvae scored as positive. Levels of naturally occurring virus remained low in the check plots. Adult emergence from the pupae collected in the treated plots ranged from 4 to 19% and from 28 to 43% in the check plots. Reduction in egg-mass density attributed to the treatments was 97% in one plot, 99% in two others, and not determined for the fourth.

A virus dosage of 8.3 × 1010 PIB per hectare, which is one-third of the previously recommended dosage, is adequate, and either tank mix is acceptable.

Résumé

En 1982, quatre placettes de 10 ha situées dans le district forestier de Kamloops, en Colombie-Britannique, qui renfermaient des douglas taxifoliés infestés par la chenille à houppes du douglas ont été traitées par des épandages aériens de diverses préparations du virus de la polyédrose nucléaire (Virtuss) au moment où la plupart des larves se trouvaient au premier stade. Une première placette a reçu une dose de 2,5 × 1011 corps d’inclusion polyédriques (CIP) par hectare sous forme d’une préparation huileuse émulsionnable, et une autre, la même dose, mais dans une préparation aqueuse contenant des mélasses. Les deux autres placettes ont reçu une préparation huileuse contenant 8,3 × 1010 CIP/ha dans un cas et 1,6 × 1010 CIP/ha dans l’autre. Les traitements ont été réalisés à l’aide d’un avion muni d’une rampe de pulvérisation étalonnée pour un débit de 9,4 L/ha. Quatre autres placettes ont été utilisées comme témoins.

Six semaines après les arrosages, la réduction de la population due au traitement (calculée suivant la formule modifiée d’Abbott) s’élevait à 65% dans la placette ayant reçu la dose la plus faible et elle variait entre 87 et 95% dans les trois autres placettes. L’infection virale, déterminée au microscope, a été maximale vers la 5e ou 6e semaine après l’arrosage, de 85–100% des larves étant alors infectées. Le niveau d’infection naturelle dans les placettes témoins est demeuré faible. On a observé des taux d’émergence d’adultes variant entre 4 et 19% chez les chrysalides récoltées dans les placettes traitées et entre 28 et 43% chez celles des placettes témoins. La réduction de la densité des masses d’oeufs attribuable au traitement a été de 97% dans une placette et de 99% dans deux autres; elle n’a pas été déterminée dans la quatrième.

On estime qu’une dose de 8,3 × 1010 CIP/ha, soit le tiers de la dose déjà recommandée, est suffisante et que les deux préparations sont acceptables.

Type
Articles
Information
The Canadian Entomologist , Volume 119 , Issue 7-8 , August 1987 , pp. 697 - 706
Copyright
Copyright © Entomological Society of Canada 1987

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