Spatial Dispersion Patterns and Sequential Sampling Plans for Squash Bugs (Heteroptera: Coreidae) in Summer Squash

Abstract

Squash bugs, Anasa tristis (De Geer), were intensively sampled in summer squash plots from three locations in Oklahoma in the spring and summer of 1987 and 1988. Data collected from whole-plant samples for adults, egg masses,and nymphs were fitted to the Poisson, negative binomial, and positive binomial frequency distributions, as well as Taylor's power function and Iwao's patchiness regression. None of the three theoretical distributions fit the squash bug populations on all sample occasions. Taylor's power law provided a better fit to the count data than did Iwao's patchiness regression. All life stages exhibited aggregated patterns of spatial dispersion;small nymphs exhibited the largest degree of aggregation, followed by large nymphs, adults, and egg masses.Sequential sampling plans for squash bugs were developed using estimated variance-mean relationships derived from Taylor's power function. Because small nymphs were highly aggregated, greater numbers of plant samples were required to estimate population means of nymphs with specified levels of precision than were needed for adults or egg masses. Validation with Monte Carlo sim- ulations indicated that these procedures may not always estimate mean population density at specified levels of precision.