The activity-density of Amara aenea (DeGeer) and Harpalus pensylvanicus (DeGeer) (Coleoptera: Carabidae) was monitored in an experiment that compared five management treatments representing a range of disturbance frequencies, crops, and aboveground biomass production. In 2004 and 2005, three treatments comprised of multiple summer cover crops were compared to bare fallow and soybean, the latter of which used mechanical cultivation to manage weeds. In 2005 weed seed predation was assessed from June to September in two of the treatments (bare fallow and oat–pea/rye–hairy vetch). Beetle activity-density varied with treatment, time of sampling, and year. In 2004 peak activity-density of A. aenea was highest in the mustard/buckwheat/canola, but there was no difference in H. pensylvanicus activity-density. In 2005 activity-density of H. pensylvanicus was higher in oat–pea/rye–hairy vetch than in soybean treatment. Seed predation rates were relatively consistent across treatments, averaging between 38 and 63%. In fallow and oat–pea/rye–hairy vetch, H. pensylvanicus activity-density accounted for 29 and 33% of the variation in seed predation, respectively. Our findings suggest cover crops have a positive effect on the activity-density of A. aenea and H. pensylvanicus and that disturbance negatively influences their activity-density in the absence of cover crops.
Nomenclature: Buckwheat, Fagopyrum esculentum Moench.; canola, Brassica napus L.; field pea, Pisum sativum L.; hairy vetch, Vicia villosa Roth; mustard, Sinapis alba L.; oat, Avena sativa L.; red clover, Trifolium pretense L.; rye, Secale cereale L.; soybean, Glycine max Merr.; Amara aenea DeGeer; Harpalus pensylvanicus DeGeer.