Eriborus terebrans (Gravenhorst) is the primary parasitoid of the European corn borer, Ostrinia nubilalis (Hübner) (Lepidoptera: PyraIidae), in Michigan. Previous studies demonstrated that early in the growing season, E. terebrans adults are more abundant, and parasitize a greater proportion of O. nubilalis larvae, near wooded edges of cornfields. We hypothesized that E. terebrans requires a source of sugar and a moderate microclimate available in the woodlot, but not in the cornfield. Growth chamber and greenhouse experiments demonstrated that longevity of E. terebrans that are provided sugar was greater than those provided only water, or neither; and wasp longevity was greater at 25 than 35°C. In field experiments, wasps were caged in cornfields, woodlots, wooded fencerows, and herbaceous vegetation, early and late in the season. Longevity of E. terebrans adults was greater in woodlots than early season cornfields. Wasps lived longer in all habitats late in the season than early in the season. In all habitats, wasp longevity was enhanced by sugar. These and previous studies indicate that E. terebrans needs habitats adjacent to cornfields for sources of sugar and a moderate microclimate unavailable in early season corn. In annual agriculture, perennial habitats adjacent to crop fields may be necessary to provide the structure, stability, and resources needed for the successful conservation of natural enemies and effective biologicalcontrol.
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Dyer et al. (1996) studied this question.