DOT Project Number:  90-00-LRTF-508

Fiscal Year:  1995

Award:  $13,750.00

Principal Investigator:  Dr. John M. Pleasants, Iowa State University, jpleasan@iastate.edu

Summary Report:

AGGREGATION SITES FOR ADULT EUROPEAN CORN BORERS (LEPIDOPTERA: CRAMBIDAE): A COMPARISON OF PRAIRIE AND NON-NATIVE VEGETATION

Moths of the European corn borer, Ostrinia nubilalis (Hübner), aggregate daily in areas of dense vegetation. They rest there during the day, and after nightfall they emerge to drink water and engage in reproductive activities. Certain types of vegetation are more preferred as aggregation sites. We investigated several physical characteristics of vegetation that might determine moth preference. We focused primarily on vegetation types that occur along roadsides adjacent to cornfields. Roadside vegetation in the Midwest typically consists of brome grass but several states have begun planting prairie vegetation. We were especially interested in the moth’s relative preference for prairie vegetation as an aggregation site compared with brome. To determine preference, sweep counts of moths were made during the first and second O. nubilalis generations at four central Iowa study sites in vegetation types which included brome grass, other non-native grasses, prairie, and mixtures of prairie and non-native vegetation. For each vegetation type we measured its microclimate and vertical structure (foliage density at 5 vertical levels). In the first generation, moths were 5.7 times more numerous in brome than in prairie. Other types of vegetation available at this time had preference values similar to prairie. In the second generation, foxtail grass, when present, had 5.7 times more moths than brome. Brome had 1.4 times as many moths as prairie. The vertical structure differences among vegetation types were strongly associated with differences in foliage density at the 60cm level. In both generations, the number of moths in different vegetation types was significantly positively correlated with their foliage density at 60cm. However, there were some vegetation types that were exceptions, which we believe is due to the role of other aspects of structure. Microclimate measurements of different vegetation types were not consistently correlated with moth abundance. This indicates that the structure of the vegetation, more than its microclimate, is the primary determinant of moth preference. We conclude that O. nubilalis moths prefer tall, dense vegetation with erect stems. We also conclude that replacing roadside brome and the weedy foxtail with native prairie has the potential to reduce the number of adult moths breeding near cornfields, especially during the first generation.