Variable-Intensity Sampling: A New Technique for Decision Making in Cabbage Pest Management1

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Abstract
A variable-intensity sampling method was developed to efficiently monitor all cabbage pests in commercial fields in New York while concentrating on the most important pests, Pieris rapae (L.) and Trichoplusia ni (Hübner). The field is walked in a V-shaped pattern which is divided into 10 segments. Along each segment, one to four randomly selected cabbage plants are inspected, the number depending on an estimate of population density of P. rapae and T. ni derived from previous segments. Computer simulations of this procedure were run, using random numbers from the appropriate negative binomial distribution, and the 95% confidence intervals calculated contained the true mean with frequencies between 93 and 97%. In a commercial cabbage field, a comparison of estimates of the means obtained by variable intensity sampling and fixed sample sizes of 40 and 264 plants revealed only small differences.