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

Abstract

AbstractA sampling plan for the estimation of the number of achenes damaged by the red sunflower seed weevil,Smicronyx fulvusLeConte, 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).