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SAMPLING PLANS FOR ESTIMATING ACHENE DAMAGE BY THE RED SUNFLOWER SEED WEEVIL (COLEOPTERA: CURCULIONIDAE)

Published online by Cambridge University Press:  31 May 2012

Chengwang Peng  and
Gary J. Brewer
Chengwang Peng
Affiliation:
Department of Entomology, North Dakota State University, Fargo, North Dakota, USA 58105
Gary J. Brewer
Affiliation:
Department of Entomology, North Dakota State University, Fargo, North Dakota, USA 58105
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Abstract

A sampling plan for the estimation of the number of achenes damaged by the red sunflower seed weevil, Smicronyx fulvus LeConte, is useful in evaluating the efficiency of weevil management strategies. The objective of this study was to determine the distribution pattern of the damaged achenes that would allow the development of a fixed-sample-size plan for estimation of the damaged achenes. Taylor’s power law and Iwao’s patchiness regression were used to analyze the distribution pattern of the damaged achenes. Slopes from both models were >1, indicating an aggregated spatial pattern. The intercepts and slopes from both models were used to calculate the minimal mean number of damaged achenes per sunflower head that can be estimated for a given sample size and precision level. If the mean number of damaged achenes per head is low (<20), the plan developed using the parameters of Taylor’s power law requires significantly more samples than the plan using the parameters of Iwao’s patchiness regression to estimate the same density of damaged achenes. If the mean number of damaged achenes per head is high (>30), the two plans give similar results. If both low and high damage situations are considered, Taylor’s plan is preferred to Iwao’s plan. At the 0.10 precision level, Taylor’s plan requires approximately 40 samples (heads) to estimate a mean of about 200 damaged achenes per head (≈ current economic injury level).

Résumé

L’élaboration d’un plan d’échantillonnage propre à estimer le nombre d’akènes endommagés par le charançon du tournesol Smicronyx fulvus LeConte peut s’avérer très utile dans l’évaluation de l’efficacité des stratégies de lutte contre l’insecte. Nous avons tenté de déterminer quel type de répartition des akènes endommagés pourrait le mieux nous aider à mettre au point un plan d’échantillonnage à échantillon de taille fixe permettant l’estimation du nombre d’akènes endommagés. La loi de Taylor et la régression de contagion d’Iwao ont été utilisées pour analyser le type de répartition des akènes endommagés. Les pentes des deux modèles étaient >1, ce qui reflète une répartition spatiale contagieuse. Les intersects et les pentes des deux modèles ont ensuite servi à calculer le nombre moyen minimal d’akènes endommagés par inflorescence qui puisse être estimé pour un échantillon de taille donnée à un niveau de précision donné. Si le nombre moyen d’akènes endommagés par inflorescence est faible (<20), le plan élaboré à partir des paramètres de la loi de Taylor demande un nombre plus grand d’échantillons que le plan élaboré à partir de la régression d’Iwao pour aboutir à la même densité d’akènes endommagés. Si le nombre moyen d’akènes endommagés par inflorescence est élevé (>30), les deux plan aboutissent aux mêmes résultats. Dans les cas où les deux situations sont prises en considération, le plan de Taylor est préférable à celui d’Iwao. À un niveau de précision de 0,10, le plan de Taylor nécessite environ 40 échantillons (inflorescences) pour estimer une moyenne d’environ 200 akènes endommagés par inflorescence (à peu près le seuil économique courant).

[Traduit par la Rédaction]

Type
Articles
Information
The Canadian Entomologist , Volume 127 , Issue 1 , February 1995 , pp. 7 - 14
Copyright
Copyright © Entomological Society of Canada 1995

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