Graduate Thesis Or Dissertation
 

Use of a geographical information system to modify pheromone trap-based predictions of Helicoverpa zea (Boddie) damage

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  • The GRASS (V. 4.0) geographical information system (GIS) was used to test the hypothesis that pheromone trap based predictions of Helicoverpa zea (Boddie) damage in processed sweet corn could be improved by considering spatial patterns of corn plantings and wind blocking features around the trap. Wind blocking features include: tree rows, wooded areas, large buildings close to the trap, and abrupt hillsides. Pheromone traps were monitored at 29 and 30 sites in 1990 and 1991. Corn development through the year and damage levels at harvest (percent infestation) were also recorded for these locations. Maps of all corn plantings and wind blocking features within 2.5 kilometers of the trap were created, digitized, and entered into the GIS for each site. A stepwise regression analysis considering 18 spatial and two non-spatial variables resulted in a highly significant (P<0.001) four variable regression model with an R² of 0.82. Spatial input variables used in this model included the total number of hectares of corn within 2.0 kilometers of the trap as well as the average distance to wind blocking features on the north side of the trap. The non-spatial variables used were cumulative trap catch and date of first silk. A dynamic simulation model was also created. This was designed to filter from the trap catch those moths coming from plantings outside of the trapped planting. This model functioned by creating map surfaces in the GIS showing for each day the relative contribution to catch for each location around the trap. This map surface was the product for each location of relative moth population levels and the likeliness that a moth positioned there would be captured by the trap. The modified cumulative trap catch was expected to correlate more strongly to damage levels than the unmodified trap catch, but no run of the model produced a significant improvement in the correlation. In the process of collecting data for this project, circumstantial evidence was obtained which indicated that high synchrony between valley-wide moth catch levels and valley-wide timings of silking in corn could be used as an indicator of high damage years.
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