Feeding preferences of weed seed predators and effect on weed emergence

We determined feeding preferences of invertebrate seed predators and the effect of seed predation on weed emergence. Feeding choice studies were completed with three species of common ground beetles: (Amara aenea DeGeer, Anisodactylus sanctaecrucis F., and Harpalus pensylvanicus DeGeer) (Coleoptera: Carabidae) and the northern field cricket (Gryllus pennsylvanicus DeGeer) (Orthoptera: Gryllidae). Anisodactylus sanctaecrucis, H. pensylvanicus, and the female and male G. pennsylvanicus consumed more redroot pigweed seeds compared with giant foxtail seeds; A. aenea seed consumption did not differ between these two weed species. All invertebrates consumed fewer velvetleaf seeds compared with redroot pigweed and giant foxtail seeds; however, when seed biomass was compared, A. aenea consumed similar biomass of velvetleaf, giant foxtail, and redroot pigweed, whereas A. sanctaecrucis and H. pensylvanicus consumed greater biomass of velvetleaf compared with giant foxtail seed. Seed burial depths of 0.5 or 1.0 cm reduced redroot pigweed and giant foxtail seed consumption by A. aenea and A. sanctaecrucis but not by the larger carabid beetle, H. pensylvanicus. In a greenhouse study, A. sanctaecrucis decreased total weed emergence by 15%, and G. pennsylvanicus females and males decreased weed emergence by 16 and 5%, respectively. Emergence of redroot pigweed, but not velvetleaf or giant foxtail, decreased when A. sanctaecrucis and the male G. pennsylvanicus were present, whereas the emergence of all three weed species decreased in the presence of the female G. pennsylvanicus. In field experiments, vertebrate access to velvetleaf seeds reduced emergence from 4 to 9% across field sites; invertebrate access reduced emergence 4 to 6%. Vertebrate access to giant foxtail seeds reduced emergence 3 to 7%, and invertebrate access reduced emergence 4 to 13%. These results suggest that predation of weed seeds by both vertebrates and invertebrates may reduce weed emergence and influence the weed community.