SPATIAL-DISPERSION AND BINOMIAL SEQUENTIAL SAMPLING FOR CITRICOLA SCALE (HOMOPTERA, COCCIDAE) ON CITRUS

A binomial (presence-absence) sequential sampling plan for citricola s cale, Coccus pseudomagnoliarum (Kuwana), was developed and validated f or infestations on orange trees. Population densities from 200 collect ions of 25 leaves in both 1991 and 1992 were used to determine the Gre en coefficient (C-x), and the intercept and slope values for both the Taylor power law and Iwao regression of mean crowding on the mean. All measures of dispersion agreed in both years that scale populations we re aggregated; C-x was > 0.3 and slopes from the regressions were sign ificantly >1 (P < 0.001). Because the fit of the regression lines was best using the Taylor power law, a binomial sampling plan was develope d incorporating power law coefficients into Wald's (1947) approach wit h upper and lower thresholds, a critical action level of 1 scale per l eaf, and a truncation at 200 samples. A minimum sample of 25 leaves co llected from different trees is recommended to minimize potential inco rrect treatment decisions caused by among-tree variation. In 11 valida tion trials in 1993, the binomial plan compared favorably with a conve ntional technique where citricola scales on 125 leaves from 5 trees we re counted. Both techniques reached the same conclusions regarding the need for treatment in 10 of 11 trials, but the binomial plan required less average time while allowing more trees to be examined.