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DEVELOPMENT AND EVALUATION OF A SAMPLING SCHEME FOR THE GYPSY MOTH1 EGG PARASITOID OOENCYRTUS KUVANAE (HYMENOPTERA: ENCYRTIDAE)2

Published online by Cambridge University Press:  31 May 2012

M. W. Brown
Affiliation:
Department of Entomology, The Pennsylvania State University, University Park 16802
James L. Rosenberger
Affiliation:
Statistics Department, The Pennsylvania State University, University Park 16802
E. Alan Cameron
Affiliation:
Department of Entomology, The Pennsylvania State University, University Park 16802

Abstract

Four sampling methods for Ooencyrtus kuvanae (Howard) populations were compared for efficiency using coefficients of variation. On this basis, none of the sampling methods was uniformly superior to any other, but a cluster of 0.01 ha subplots was chosen as the best method because of the aggregation of both gypsy moth egg masses and parasitoids. From the estimated population variance per egg mass it was calculated that 150 egg masses should be sampled per plot to provide an error bound of 0.2 parasitoid per egg mass (α = 0.1). An analysis of variance indicated that variation among study areas was the largest source of variation, and that among day, within day, and plot configuration variation were significant. Estimates of parasitoid activity are most reliable during the period between 1300 and 1600 h EST. Activity of parasitoids was reduced on overcast days. In August, the distribution of O. kuvanae approximates that of the negative binomial but with too many individuals in the high frequency classes. In a compromise between cost and accuracy, the sampling scheme selected consists of thirty 0.01 ha subplots per plot sampled between 1300 and 1600 h EST on sunny days. This sampling scheme was found satisfactory using field evaluation.

Résumé

Quatre méthodes d’échantillonnage des populations d’Ooencyrtus kuvanae (Howard) ont été comparées pour leur efficacité à l’aide des coefficients de variation. Aucune des méthodes d’échantillonnage ne s’est avérée uniformément supérieure à l’une des autres, mais un ensemble de sous-parcelles de 0.01 ha a été retenu comme étant la meilleure méthode étant donné l’aggregation à la fois des masses d’oeufs de la spongieuse et des parasitoïides. A partir de l’estimé de la variance de population par masse d’oeuf, il a été calculé que 150 masses d’oeufs devraient être échantillonnées par parcelle afin d’avoir une erreur limite de 0.2 parasitoïide par masse d’oeufs (α = 0.1). L’analyse de variance a montré que la variation entre les sites d’étude représente la source majeure de variation, et que la variation inter-jours et intra-jours, et la variation due à la configuration de la parcelle étaient significatives. Les estimés de l’activité du parasitoïide montrent leur fiabilité maximum entre 1300 h et 1600 h HNE. L’activité des parasitoïides était réduite par temps couvert. En août, la distribution d’O. kuvanae approche la binomiale négative avec cependant un surplus d’individus dans les classes de fréquence élevée. Un compromis entre le coût et la précision, la formule d’échantillonnage retenue consiste en 30 sous-parcelles de 0.01 ha par parcelle échantillonnées entre 1300 h et 1600 h HNE par jours ensoleillés. Cette formule d’échantillonnage s’est avérée satisfaisante à l’essai sur le terrain.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1981

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