Clumping Patterns of Fruit and Arthropods in Cotton, with Implications for Binomial Sampling

Abstract

A binomial model is presented which enables the clumping patterns of different species or categories of cotton arthropods and plant parts to be compared, accounting for the effect of their densities. Estimates of the proportion of infested sample units derived with this model are compared with those derived with three other binomial models. Statistical comparison is made, using as a criterion the degree to which each model fit field values of the proportion of infested sample units collected by three sampling methods (visual whole-plant examination, a bag method, and sweep-net). Those models which fail to incorporate the effect of density on clumping behavior fit the data less well. Estimates of sample sizes derived by a binomial sample size equation and a numerical sample size equation both of which incorporate species clumping behavior are also compared. The sample size estimates from the two equations are most similar at low densities and for species whose distributions appear closest to random; and although binomial sampling requires a larger sample size at higher densities, less time is required to sample each unit (leaf, plant, etc.).