SEQUENTIAL SAMPLING PLANS FOR USE IN TIMING INSECTICIDE APPLICATIONS FOR CONTROL OF EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE) IN POTATO

Sequential sampling plans were developed for use in recommending contr ol of European corn borer, Ostrinia nubilalis (Hubner), in potato, Sol anum tuberosum L., fields based on the distribution of damaged stems. Likelihood ratio tests indicated that the beta-binomial distribution ( aggregated) provided a better fit than the binomial (random) when the mean percentage of damaged stems in a field was greater than or equal to 6%, but not when damage was <6%. Similarly, variance-ratio (D) and C(alpha) tests indicated that damage was aggregated generally at damag e levels greater than or equal to 6%. Because the slope (b) +/- SEM of the binary form of the Taylor power law (1.15 +/- 0.05) (total of 41 fields) revealed moderate overdispersion, and a weak linear relationsh ip existed between the index of aggregation (theta) and p, sequential sampling plans were evaluated under various degrees of aggregation. Th e precision and practicality of the sequential sampling plans were eva luated through calculation of operational characteristics and average sample number functions for both simulated binomial and beta-binomial distributions. Precision of the sequential sampling plans decreased as the aggregation of O. nubilalis damage increased, especially when the proportion of damaged stems was near threshold. However, precision in creased dramatically if fields near threshold were sampled more than o nce. Because, in practice, potato fields near threshold are sampled re peatedly, the sampling plans were considered acceptable. A comparison between the sequential sampling plan and the conventional sampling pla n revealed that control decisions made using the sequential plan agree d closely with those made by the conventional plan, and averaged 57% f ewer samples needed to make the decision.