Journal of Economic Entomology

Published by: Entomological Society of America

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Journal of Economic Entomology 97(3):1003-1008. 2004
doi: 10.1603/0022-0493(2004)097[1003:BSSPFL]2.0.CO;2

Binomial Sequential Sampling Plans for Late Instars of European Corn Borer (Lepidoptera: Crambidae), Corn Earworm (Lepidoptera: Noctuidae), and Damaged Kernels in Sweet Corn Ears

Patrick K. O’Rourke and W. D. Hutchison

Department of Entomology, University of Minnesota, 1980 Folwell Avenue, St. Paul, Minnesota 55108–6125

Abstract

Late-season infestations of European corn borer, Ostrinia nubilalis (Hübner), and corn earworm, Helicoverpa zea (Boddie), were sampled to develop binomial sequential sampling plans for larval infestations and damaged kernels in sweet corn, Zea mays L., ears, near harvest. Fields were sampled to obtain a range of larval densities likely to be encountered over a range of infestation levels and field conditions. Binomial sampling plans were developed for O. nubilalis larvae, H. zea larvae, O. nubilalis, and H. zea larvae combined, and for damaged sweet corn kernels. Observed densities ranged from 0.01 to 4.40 larvae per ear for O. nubilalis, 0.005–1.62 larvae per ear for H. zea, and 0.004–36.12 damaged kernels per ear. Results of resampling analyses, based on the proportion of ears infested with one or more larvae, or damaged kernels, indicated an average sample size of 34–37 ears was necessary to classify whether larval infestations, or the incidence of damaged kernels, exceeded 5%. Two operating characteristic curves are presented for each of the four sampling plans. Initial results, with upper bounds of 0.10, and α (type I) and β (type II) error rates at 0.10 and 0.05, respectively, resulted in a 90% probability of making the correct management decision at infestation levels >10%. To improve performance of the sampling plans, we modified the binomial plans by reducing the upper bound to 0.075, while maintaining the same error rates. This plan resulted in a higher probability (>95%) of making the correct management decision to reject a sweet corn load when infestation levels are >10%.

Received: September 10, 2003; Accepted: March 29, 2004

Keywords: Ostrinia nubilalis, Helicoverpa zea, sweet corn, binomial sequential sampling



References

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Fig. 1. OC function for the binomial sequential sampling plan by using a sample unit of one ear. Operating characteristic was plotted against proportion of sample ears infested with >1 larva per ear (A–C) or >1 damaged kernel (D). Proportion of ears infested was obtained from resampling software with α = 0.10, β = 0.05, action threshold of 0.05, minimum sample size of 25 ears, and tally threshold of 1. Predicted lines were fit to observed data by using the equation ln(y) = a + bx1.5. Two curves are represented on each figure, one showing a line using θ1 = 0.01, θ2 = 0.10 and one using θ1 = 0.01, θ2 = 0.075. For purposes of graphical clarity, the proportion of infested ears was limited to 0.30 rather than extended to 1.0 on the x-axis

Fig. 2. ASN function for the binomial sequential sampling plan by using a sample unit of one ear. Average sample number was plotted against proportion of sample ears infested with >1 larva per ear (A–C) or >1 damaged kernel (D). The average sample number was plotted against observed proportion infested obtained from resampling software with α = 0.10, β = 0.05, action threshold of 0.05, minimum sample size of 25 ears, and tally threshold of 1. Predicted lines were fit to observed data by using the equation [logistic] y = a + 4bn (1 + n)2 for all four sampling plans. For purposes of graphical clarity, the proportion of infested ears was limited to 0.20 rather than extended to 1.0 on the x-axis

Fig. 3. Decision stop lines for the pooled binomial sequential sampling plans based on resampling validation analyses for O. nubilalis or H. zea individually, O. nubilalis and H. zea combined, and damaged kernels. Sample unit is one ear, α = 0.10, β = 0.05, action threshold of 0.05, tally threshold of 1, and minimum sample size is 25 ears

table

Table 1. Resampling results for late-instar O. nubilalis and H. zea and damaged kernels in sweet corn ears where upper bound was set at 0.10

table

Table 2. Resampling results for late-instar O. nubilalis and H. zea and damaged kernels in sweet corn ears where the upper bound was reduced to 0.075

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