Spatial Distribution of the Red Sunflower Seed Weevil (Coleoptera: Curculionidae) on Sunflower

Abstract

Knowledge of the distribution of counts of an insect is an essential element for development of a sequential sampling plan. The objectives of this study were to determine the spatial distribution of red sunflower seed weevil, Smicronyx fulvus Le-Conte, counts in sunflower, and to determine the effect of plant stage on the density. Taylor's power law, Iwao's patchiness regression, and the negative binomial probability model were used to analyze the data. All three indices ( b , β, and k ) indicated an aggregated distribution of the weevil. Taylor's power law provided a better description than Iwao's patchiness regression. The negative binomial distribution parameter k was not dependent with mean density, indicating the presence of a common k ( kc ). The estimates of kc ranged from 0.4587 to 0.5255. Plant growth stage had a significant effect on the density of the weevil. When most plants were in the bud stages, more weevils were always found in the blooming sunflower heads (>R5.0 stage). When plants were in the anthesis stage (R5.0–6.0), the adult weevils preferred plants of stage R5.4–6.0, which were suitable for oviposition.