Eriborus terebrans (Cravenhorst) is the most abundant parasitoid of the European cornborer, Ostrinia nubilalis (Hubner), in Michigan. The within-field distribution of adult E. terebrans was sampled ...in 1991 and 1992 by placing malaise traps near a wooded edge, near an herbaceous edge, and in the field interior in each of 4 fields of corn, Zea mays L. During the 1st generation of 1991, significantly more females were captured in wooded-edge traps than in herbaceous-edge or interior traps. In the 1st generation of 1992, more females were again captured in wooded-edge traps in 2 fields, whereas in the other 2 fields, more were captured in both herbaceous-edge and wooded-edge traps than interior traps. In the 2nd generation of both years, there was no consistent pattern of distribution of adult females among sites. The distribution pattern of adult females among fields was not consistently correlated with the distribution of O. nubilalis larvae or percentage parasitism. Overall, fewer males were captured than females, and in the 1st generation of both years, more males were captured near wooded edges of cornfields in which the previous crop had been corn, than any other sites. Both male and female E. terebrans were captured in malaise traps at the interface of a woodlot canopy and a cornfield with capture zones from 1 to 4.3 m high. We propose that E. terebrans distribution in cornfields is influenced by resources such as sugar and a moderate microclimate present in adjacent woodlots but unavailable in early-season cornfields. Perennial noncrop habitats may play an important role in conservation of natural enemies for biological control
Ground beetles are polyphagous predators that often colonize cereal fields from adjacent habitats. Boundaries separating these habitats may filter the movement of species across them resulting in ...differences in species composition among the habitats. Ground beetles were captured in spring 1995 at 3 sites, autumn through spring 1995-1996 at 4 sites, and autumn through spring 1996-1997 at 2 sites using pitfall traps positioned in riparian strips, wheat fields, and along riparian-wheat field edges. Canonical correspondence analysis was used to arrange ground beetles along temporal and spatial gradients. Autumn and spring assemblages of ground beetles were separated along the 1st canonical axis. The 2nd canonical axis further separated spring and winter assemblages of ground beetles. With the effects of season removed, ground beetles were classified with respect to habitat association along axes 1 and 2 of a partial canonical correspondence analysis. Based on this analysis, ground beetles occupying wheat field interiors and wheat field edges were separated from those occupying riparian interiors and riparian edges along the 1st canonical axis. The 2nd canonical axis separated beetles occupying interior habitats from those occupying edge habitats. We classified beetles as habitat generalists, wheat specialists, riparian specialists, or boundary specialists. Riparian areas may serve as permanent habitats for ground beetles to colonize cereal fields. Because of their continuous seasonal activity and predatory nature many species of ground beetles are good candidates for biological control of wheat pests.
