Behavioural Studies ofHarpalus rufipesDe Geer: an Important Weed Seed Predator in Northeastern US Agroecosystems

Harpalus rufipes, a member of the Carabidae, is the most common granivorous invertebrate in Maine agroecosystems. While previous research demonstrated a positive correlation between H. rufipes activity-density and weed seed predation, little is known about the behaviour of this seed predator. We conducted mesocosm experiments to examine seed burial, soil surface conditions, and seed mass effects while tracking H. rufipes movement using a video camera, capture card, and EthoVision software. H. rufipes showed a preference (<0.001), for seeds on the soil surface compared to those half or fully buried. Species with larger seeds were preferred, but Amaranthus retroflexus, which had the smallest seeds, had the highest feeding efficiency (i.e., seeds eaten per distance travelled). Undisturbed soil resulted in highest predation rates, presumably because seeds were easier to detect relative to disturbed soil. Video-tracking measurements of duration within areas of particular seeds, and efficiency of seed predation, indicate that H. rufipes behaviour is prey dependent