Sequential sampling plans for use in timing insecticide applications for control of European corn borer (Lepidoptera: Pyralidae) in potato
Nault, B.A. | Kennedy, G.G.
Sequential sampling plans were developed for use in recommending control of European corn borer, Ostrinia nubilalis (Hubner), in potato, Solanum 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 6%, but not when damage was <6%. Similarly, variance-ratio (D) and C(alpha) tests indicated that damage was aggregated generally at damage levels greater than 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 relationship existed between the index of aggregation (theta) and p, sequential sampling plans were evaluated under various degrees of aggregation. The precision and practicality of the sequential sampling plans were evaluated through calculation of operational characteristic 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 increased dramatically if fields near threshold were sampled more than once. Because, in practice, potato fields near threshold are sampled repeatedly, the sampling plans were considered acceptable. A comparison between the sequential sampling plan and the conventional sampling plan revealed that control decisions made using the sequential plan agreed closely with those made by the conventional plan, and averaged 57% fewer samples needed to make the decision.
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