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Title: Sequential sampling for panicle caterpillars (Lepidoptera: Noctuidae) in sorghum

Author
item Elliott, Norman - Norm
item BREWER, MICHAEL - Oklahoma State University
item GILES, KRISTOPHER - Oklahoma State University
item BACKOULOU, GEORGES - Oklahoma State University
item MCCORNACK, BRIAN - Kansas State University
item PENDLETON, BONNIE - West Texas A & M University
item ROYER, THOMAS - Oklahoma State University

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2014
Publication Date: 3/15/2014
Citation: Elliott, N.C., Brewer, M.J., Giles, K.L., Backoulou, G.F., McCornack, B.P., Pendleton, B.B., Royer, T.A. 2014. Sequential sampling for panicle caterpillars (Lepidoptera: Noctuidae) in sorghum. Journal of Economic Entomology. 107(2):846-853.

Interpretive Summary: Sorghum panicle worm (commonly called the sorghum headworm) is an economically important insect pest complex of sorghum throughout the Great Plains of the United States, particularly in Texas, Oklahoma, and Kansas. The headworm complex consists of larvae of two moth species. We developed a sequential sampling plan for headworms. A sequential sampling plan was developed using a high threshold (an economic threshold) of 0.5 headworms per sorghum head, a low threshold (a safe level) of 0.20 headworms per head, and fixed error rates consistent with levels growers require for economically reliable decision-making. The plan improves upon current sampling recommendations of 30 heads inspected per 40 acre sorghum field because at known acceptable error rates fewer samples are required at low and high headworm densities to make a decision to treat or not to treat a field with insecticide. When densities are near the economic threshold a larger number of samples than 30 is required to make decisions, but in this case the decisions are made with fixed acceptable error rates. The sequential sampling plan will improve headworm pest management in sorghum, saving growers time and money.

Technical Abstract: Sorghum panicle worm is an economically important insect pest complex of sorghum throughout the Great Plains of the United States, particularly in Texas, Oklahoma, and Kansas. The sorghum panicle worm complex consists of larvae of two highly polyphagous lepidopteran species: the corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J.E. Smith) [Lepidoptera: Noctuidae]. Sampling for panicle worms in grain sorghum fields is usually accomplished by the beat bucket sampling technique with a fixed sample size of 30 beat bucket samples of one sorghum head each per 16.2 ha field. We developed a sequential sampling plan for panicle worms based on Wald's Sequential Probability Ratio Test for a negative binomial distribution. A total of 115 grain sorghum fields were sampled in Texas, Oklahoma, and Kansas from June-August 2010. Panicle worms had an aggregated distribution of counts confirmed by Pearson's chi-square statistic for lack of fit to the negative binomial distribution for each sampled field. A sequential sampling plan was developed using a high threshold (an economic threshold) of 0.5 panicle worms per sorghum head, a low threshold (a safe level) of 0.20 panicle worms per head, and fixed error rates (alpha = 0.10 and beta = 0.05). At panicle worm densities >0.45 per head and < 0.12 per head, the average number of heads inspected to make a decision is less than the current recommendation of 30 heads. The plan improves upon current sampling recommendations for panicle worms in grain sorghum because at known acceptable fixed error rates fewer samples are required at low and high panicle worm densities, while a larger number of samples is required to make decisions with the same acceptable error rates when densities are near the thresholds.