Dispersion Statistics and Sequential Sampling Plan for Adult Pear Psylla12

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Abstract
Reported here are dispersion statistics associated with a beating-tray method of sampling and sequential sampling procedures which optimize time spent estimating adult pear psylla densities. Psylla pyricola Foerster adults do not form cohesive groups or colonies such as aphids, but they do show a definite contagious distribution. Beating-tray samples taken during the early growing season, before foliage had developed, were slightly more variable, suggesting they were less efficient in estimating density than those taken after foliage developed. Insecticide applications did not affect the dispersion of pear psylla adults. Calculated stop lines for estimating adult pear psylla densities within 50% of the mean indicate minimum samples of 5, 8, and 12 trays at error levels of P = 0.2, 0.1, and 0.05.

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