PROBABILITY OF DETECTING NEMATODE INFESTATIONS IN QUARANTINE SAMPLES

In quarantine and certification programs, intensive sampling may be ne eded to determine if lots or shipments of planes, pots, cuttings, or o ther units are free of plant-parasitic nematodes and other plant pests . It is essential for each quarantine program to define an acceptable tolerance limit for each pest sampled, recognizing that zero tolerance requires sampling everything in the shipment, which is usually imprac tical. The binomial and hypergeometric probability distributions were used as bases for determining probabilities of detecting various infes tation levels as increasing numbers of samples are collected. Probabil ities of detecting infestations of 50%, 10%, 5%, 1%, or 1 unit in lot sizes of 100, 1 000, 10 000, and 100 000 units are provided for select ed numbers of samples. According to the binomial probability distribut ion, if 5% of the units in a lot are infested, 59 and 90 samples, resp ectively, would be required to detect the infestation 95% and 99% of t he time. When only 1% of the units are infested, sample sizes must be increased to 300 and 500 for 95% and 99% detection, respectively. Subj ect to certain assumptions, methodology is provided to estimate the pr obability of detection for various lot and sample sizes.