Quadrat Sample Precision and Cost with a High-vacuum Insect Sampling Machine in Cotton Ecosystems

Abstract

Accurate and reliable insect samplers must be used in an effective manner if predators are to be used in the integrated pest management (IPM) decision-making process for complex ecosystems; therefore, optimum sampling procedures were evaluated for a high-vacuum insect sampling machine (Insectavac) for use in cotton, Gossypium hirsutum L. A total of 15 adult and immature insect groups was collected from 3 cotton fields, 12 times over a 3-yr period with an Insectavac. These data were used to evaluate the effect of quadrat size and number on the cost and precision of sampling in a cotton ecosystem. We sampled 340, 30.5-m quadrats end to end and 250, 61.0-m quadrats were sampled in a randomized complete block design over a 3-yr period. Data were analyzed using analysis of variance (ANOVA) and jackknife procedures. Variances obtained from the jackknife procedure were essentially the same as those obtained from the ANOVA. We concluded that sampling biases caused by patchy or clumped distributions of insects were not significant and the resulting estimates were unbiased. Because the insect populations were not significantly clumped, nothing was gained by the use of the jackknife procedure. Large quadrats resulted in significantly greater sampling variability because the extreme values from uneven distributions were higher than with smaller quadrat sizes. Advantages of small quadrats include a greater number of quadrats sampled for similar labor input which results in more degrees of freedom, better coverage of habitats within a field, and better representation of average insect densities.