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Improved Transect Sampling to Enhance Efficiency of Corn Rootworm Monitoring 2003

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Principle Investigators: John E. Losey, Leslie L. Allee, and J. Keith Waldron

Cornell Department of Entomology, IPM Support Staff, Ithaca

Cooperators: Elson J. Shields

Abstract:

Crop monitoring for corn rootworm remains the best means to assess fields at risk from this pest if replanted to corn the following year. Use of sequential sampling reduced the minimum sampling time to about 20 minutes or less per field per visit to make a management decision. With previous funding from the NYSIPM program we developed a transect sampling protocol for sequential sampling that reduced sampling time by an additional 6 minutes per field. Our previous results were based on a relatively small number of fields (3) and simulations over a realistic but limited range of adult CRW spatial dispersion patterns. In this project we compared transect sampling to the commonly used systematic “W” system in 13 fields. Field trials using systematic, and transect sampling in each field were used to compare the categorization of adult corn rootworm 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 time divided by plants observed were compared between sampling methods. The two methods did not differ significantly in the number of plants evaluated or in the categorization of corn rootworm populations. Transect sampling resulted in a significantly shorter time divided by plants observed (38 s), than the systematic sampling method (70 s). Based on these field results transect sampling reduces sampling time 46% compared with systematic sampling and thus could be used to reduce total sampling times substantially. While much larger number of fields sampled in this study almost certainly increased the range of spatial dispersions encountered there is still some question regarding the performance of transect sampling in fields where CRW adults are highly aggregated or clumped. Computer simulations on a wide range of dispersal patterns are continuing but early results suggest that transect sampling performs acceptably well even at the extreme ranges of potential aggregation. Furthermore, our ongoing assessment of adult CRW dispersion utilizing sticky card does not indicate extreme levels of aggregation. Computer simulations and analysis using spatial statistics continue but all of our results to date suggest that transect sampling is effective and reliable.