Spatial Distribution of Thrips in Greenhouse Cucumber and Development of a Fixed-Precision Sampling Plan for Estimating Population Density

Dispersion patterns of phytophagous thrips (Thysanoptera: Thripidae) were determined for greenhouse cucumber, Cucumis sativus L., in Cheju-do, Korea, during 1995 and 1996. Thrips populations were sampled using leaf sample, yellow sticky trap and visual estimate concurrently on each sampling date. Frankliniella occidentalis (Pergande) was the most dominant thrips species, accounting 92% of all specimens collected from leaf samples and yellow sticky traps. Dispersion indices generated by Taylor's power law and Iwao's patchiness regression were compared. Generally, Taylor's power law provided better description of mean-variance relationship than did Iwao's patchiness regression with exception of the data from the sticky trap. Slopes and intercepts of Taylor's power law from leaf sample and visual estimate did not differ among thrips species and surveyed greenhouses. A fixed-precision-level of sequential sampling plan was developed using Taylor's power law parameters generated from total number of thrips in leaf sample and visual estimate. This sampling plan for visual estimate was tested with sequential resampling simulation using 4 independent data sets. Resampling simulation analysis demonstrated that actual D values were always less than desired D values of 0.20, 0.25 and 0.30.