Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 19, 2000
Publication Date: N/A
Interpretive Summary: Ground beetles number approximately 40,000 species worldwide, and they eat a variety of agricultural pests. Ground beetles usually disperse by walking into agricultural fields from surrounding natural habitats. Little is known about ground beetles in wheat fields surrounded by both grasslands and riparian zones, and we wanted to know if ground beetle species in wheat fields adjacent to grasslands differed from those in wheat fields adjacent to riparian zones. We also wanted to determine whether beetles dispersed from the natural habitats into the wheat fields. We collected ground beetles in winter wheat fields and adjacent grasslands and riparian zones. Ground beetle abundance showed two activity peaks, one in autumn and the other in spring. Distinct groups of ground beetles were found in autumn, winter, and spring. Four distinct groups of beetles were also identified based on habitats. Grassland, grassland edge, and riparian edge had similar rspecies. Riparian interior species were completely different from the othe habitats. Beetle species in wheat adjacent to riparian zones were different from those in wheat adjacent to grasslands. We determined that many species disperse from the natural habitats into the wheat fields. Riparian zones and grasslands surrounding wheat fields provide habitats important to the survival of ground beetles and thus to the benefit of farmers.
Technical Abstract: Natural habitats surrounding agricultural fields provide a source of natural enemies to assist in pest control. The boundaries among landscape elements filters the dispersal of organisms across them, resulting in differential community structures within the landscape elements. Ground beetles are numerous, beneficial predators, and generally disperse by walking. These qualities make them excellent organisms to study boundary dynamics in agricultural landscapes. Ground beetles were captured in autumn through spring 1996 1997 at 2 sites using pitfall traps placed in wheat fields and adjacent grasslands and riparian zones. Ground beetle abundance showed two activity peaks, one in autumn and the other in spring. Species composition was most strongly related to these seasons. Axis 1 of a canonical correspondence analysis (CCA) separated spring active beetles from autumn active beetles. Axis 2 separated winter active beetles. With the effects of season and sites removed, axes 1 and 2 of a partial CCA separated beetles with respect to habitat preference. Axis 1 separated beetles into wheat and natural habitat assemblages. Axis 2 separated beetles into wheat assemblages adjacent to grasslands and wheat assemblages adjacent to riparian zones. Axis 2 also separated grassland, grassland edge, and riparian edge assemblages from riparian assemblages. Net dispersal of beetles across the boundaries showed no consistent dispersal patterns during autumn, winter, or spring. However, mark-recapture studies showed that several species routinely cross the boundaries, which resulted in differential community structures and in the increase in abundance of beetles in the wheat interiors during spring.