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Principle Investigators: John E. Losey1,
Leslie L. Allee1, and J. Keith Waldron 2
Cornell 1Department of Entomology, 2IPM Support
Staff, Ithaca
Cooperators: Elson J. Shields1
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.
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