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Transect Sampling to Enhance Efficiency of Corn Rootworm (Coleoptera: Chrysomelidae) Monitoring 2002

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Project Leaders: John E. Losey1, Leslie L. Allee1, Vladimir Zbarsky2, J. Keith Waldron3, Elson J. Shields1

1Department of Entomology, 2Cornell Institute for Social and Economic Research, 3New York State Integrated Pest Management Program, Cornell University, Ithaca, NY 14853

Abstract: Crop monitoring for adult corn rootworms, Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence, remains the best means to assess fields at risk from this pest if replanted to corn, Zea mays (L.). Improvements in sampling methodology including the development of a sequential sampling plan have reduced the minimum sampling time required to make a management decision to 20 minutes or less per field per visit to make a management decision. Many growers and scouts still find this time commitment a constraint to repeated scouting. A common currently used sampling method involves systematically covering most of the field following a “W” pattern. The feasibility of replacing the current sampling pattern with a simpler and less time-consuming transect (straight line) pattern was assessed. Computer simulations demonstrated that treatment decisions based on transect sampling would have an acceptably low error rate (10%) over a range of realistic CRW densities (0 to 2 adults per plant). This error rate represented a decrease in accuracy of less than 1% compared to systematic sampling. Field trials using transect, systematic “W”, and random sampling methods in each field were used to compare the categorization of adult CRW densities into “above” or “below” threshold with a sequential sampling plan. Efficiency measured in time to reach a decision, number of corn plants evaluated, and sampling time per plant were compared between sampling methods. The three methods did not differ significantly in the number of plants evaluated or in the categorization of CRW populations. Transect sampling resulted in significantly shorter mean sampling time per plant (38 s) than either systematic (78 s) or random sampling methods (166 s). Based on these results transect sampling reduces sampling time per plant by 40 s or 51% compared to systematic sampling and thus could reduce total sampling times substantially.

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