Cover Crops and Disturbance Influence Activity-Density of Weed Seed PredatorsAmara aeneaandHarpalus pensylvanicus(Coleoptera: Carabidae)

Abstract

The activity-density ofAmara aenea(DeGeer) andHarpalus 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 ofA. aeneawas highest in the mustard/buckwheat/canola, but there was no difference inH. pensylvanicusactivity-density. In 2005 activity-density ofH. pensylvanicuswas 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. pensylvanicusactivity-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 ofA. aeneaandH. pensylvanicusand that disturbance negatively influences their activity-density in the absence of cover crops.