SAMPLING AND BIOSTATISTICS Fixed Precision Sequential Sampling Plans for the Greenbug and Bird Cherry-Oat Aphid (Homoptera: Aphididae) in Winter Wheat N. C. ELLIOTT, 1 K. L. GILES, 2 T. A. ROYER, 2 S. D. KINDLER, F. L. TAO, 2 D. B. JONES, 2 AND G. W. CUPERUS 2 USDAÐARS, SPA, Plant Science and Water Conservation Research Laboratory, 1301 N. Western Street, Stillwater, OK 74075 J. Econ. Entomol. 96(5): 1585Ð1593 (2003) ABSTRACT The numbers of greenbugs, Schizaphis graminum (Rondani), and bird cherry-oat aphids, Rhopalosiphum padi L.,perwheattiller(stem)wereestimatedin189productionwinterwheat (Triticum aestivum L.) Þelds located throughout Oklahoma. TaylorÕs power law regressions were calculatedfromthesedataandusedtoconstructÞxedprecisionsequentialsamplingschemesforeach species. An evaluation data set was constructed from 240 samples taken during three growing seasons from winter wheat Þelds at four locations in Oklahoma. Wheat cultivar and growth stage were recorded for each Þeld on the day of sampling. TaylorÕs power law parameters for evaluation Þelds differed signiÞcantly for both species among growing seasons, locations, and plant growth stages. Median precision achieved using the Þxed precision sequential sampling schemes for each species departed 20% from expected precision over the range population intensity in the evaluation data. For the 10% of samples with greatest deviation between observed and expected precision, observed precision was 13.8Ð81.8% greater than that expected precision depending on aphid species and populationintensity.Forthegreenbug,thedistributionofthepercentagedeviationbetweenobserved and expected precision was positively skewed, so that the sampling scheme tended to over-predict precision. For the bird cherry-oat aphid, the distribution was more symmetric. Even though precision observed using the sampling schemes frequently varied from expected precision, because of the inevitable consequence of sampling error and environmental variation, the sampling schemes yielded median observed precision levels close to expected precision levels over a broad range of population intensity. KEY WORDS sequential sampling, winter wheat, cereal aphids, Schizaphis graminum, Rhopalosi- phum padi APPROXIMATELY 2.2 MILLION ha of winter wheat, Triti- cum aestivum L., are planted in Oklahoma annually. The greenbug, Schizaphis graminum (Rondani), and bird cherry-oat aphid, Rhopalosiphum padi L., com- monly infest winter wheat in Oklahoma, and damage caused by either species can reduce yields (Royer et al. 1998). The greenbug causes severe damage to win- ter wheat in Oklahoma, with estimates of economic losses $100 million in some years (Webster 1995). Although yield loss to the bird cherry-oat aphid has notbeenstudiedinwinterwheatinOklahoma,studies on spring wheat in the northern plains and winter wheat in the northwest United States have demon- stratedthatthebirdcherry-oataphidcansigniÞcantly affect root growth and reduce grain yield (Pike and Schaffner 1985, Kieckhefer and Kantack 1988, Riedell and Kieckhefer 1995, Riedell et al. 1999). Sequential sampling schemes for estimating the population intensity of greenbugs and bird cherry-oat aphids in wheat Þelds with Þxed statistical precision would be valuable for ecological and pest manage- ment research in winter wheat because they would facilitate efÞcient use of time spent estimating popu- lation intensity. Fixed precision sequential sampling schemes could also be used for decision making rel- ativetotreatmentthresholdsinoperationalintegrated pest management (IPM) programs, but that is not the intended use of the Þxed precision sequential sam- plingschemesdevelopedinthisstudy.Sequentialsam- pling schemes based on binomial counts are more practical than Þxed precision schemes for use in op- erational IPM programs, and have been developed for the greenbug and bird cherry-oat aphid in Oklahoma winter wheat (Giles et al. 2000a, 2000b). Fixed precision sequential sampling schemes are basedonmathematicalmodels,suchasTaylorÕspower law (Taylor 1961), which in our circumstance ex- presses the sample variance as a function of the mean number of aphids per stem. Sampling schemes are 1 E-mail: nelliott@pswcrl.ars.usda.gov. 2 Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078Ð3033. Downloaded from https://academic.oup.com/jee/article/96/5/1585/2217874 by guest on 11 July 2022