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PEST MANAGEMENT OF DOUGLAS-FIR TUSSOCK MOTH (LEPIDOPTERA: LYMANTRIIDAE): A SEQUENTIAL SAMPLING METHOD TO DETERMINE EGG MASS DENSITY

Published online by Cambridge University Press:  31 May 2012

R. F. Shepherd ,
I. S. Otvos  and
R. J. Chorney
R. F. Shepherd
Affiliation:
Pacific Forest Research Centre, Canadian Forestry Service, Victoria, British Columbia V8Z 1M5
I. S. Otvos
Affiliation:
Pacific Forest Research Centre, Canadian Forestry Service, Victoria, British Columbia V8Z 1M5
R. J. Chorney
Affiliation:
British Columbia Ministry of Forests, Kamloops, British Columbia V2C 2T7
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Abstract

A sequential egg-mass sample system for Douglas-fir tussock moth, Orgyia pseudotsugata McDunnough (Lepidoptera: Lymantriidae), was designed, based on visual scanning of the lower branches of Douglas-fir trees, Pseudotsuga menziesii (Mirb.) Franco. A branch was removed from each quadrant from the upper, middle and lower crown level, and from the lowest whorl of a total of 59 non-defoliated trees in 10 areas. No consistent trend in egg-mass density per branch could be found between crown levels and no level proved superior as a representative of the tree. Therefore, the lower whorl of branches was selected for survey purposes because of sampling efficiency. Sample stop lines were determined from egg-mass density and variability data collected on 55 sites and subsequent defoliation estimates were related to these densities. The system is designed as an early detection tool to be used only in non-defoliated stands at the incipient stage of an impending outbreak.

Résumé

Un plan d'échantillonnage séquentiel des masses d'oeufs de la chenille à houppes du Douglas (Orgyia pseudotsugata McD.) a été mis sur pied à partir de l'observation visuelle des branches inferieures de Douglas taxifoliés (Pseudotsuga menziesii (Mirb.) Franco). Dans chaque cadran, une branche a été prélevée dans le bas, le milieu et le haut de la cime et sur la plus basse verticelle de 59 arbres, dans 10 régions. Comme aucune tendance nette de la densité des oeufs par branche n'a pu être trouvée entre les différents niveaux de la cime dans les peuplements infestés, on a choisi, pour plus de commodité, les trois branches les plus basses comme unité d'échantillonnage. Les données techniques des échantillons ont été déterminées à partir des densités et de la variabilité observées dans 55 stations, et les estimations de la défoliation subséquente ont été corrélées à ces densités. Le plan est destiné à la détection précoce du début d'une infestation imminente, uniquement dans les peuplements non défoliés.

Type
Articles
Information
The Canadian Entomologist , Volume 116 , Issue 7 , July 1984 , pp. 1041 - 1049
Copyright
Copyright © Entomological Society of Canada 1984

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