Published online by Cambridge University Press: 20 January 2017
The utility of biological control for weed management in agroecosystems willincrease with a greater understanding of the relationships between commonweed and granivore species. Giant foxtail is an introduced, summer annualgrass weed that is common throughout the United States and problematic innumerous crops. Harpalus pensylvanicus (DeGeer)(Coleoptera: Carabidae) is a common, native, omnivorous carabid beetle witha range that overlaps giant foxtail. In 2004 and 2005, H. pensylvanicus was captured from farm fields in Centre County,PA, and subjected to laboratory feeding trials to test the preference ofgiant foxtail and other species on predation by H. pensylvanicus. Weed species seed preference experiments thatincluded “Choice” and “No Choice” treatments were conducted using giantfoxtail, common lambsquarters, and velvetleaf. When given a choice amongstthe three weed species, H. pensylvanicus preferred giantfoxtail and common lambsquarters seeds equally compared to velvetleaf seeds.When given the choice, H. pensylvanicus preferred newlydispersed giant foxtail seeds over field-aged seeds. Phenology of giantfoxtail seed shed relative to H. pensylvanicus activitydensity was also quantified in field experiments in 2005 and 2006. Giantfoxtail seed rain was determined by collecting shed seeds from Augustthrough October using pan traps. Activity density of H. pensylvanicus was monitored for 72-h periods using pitfall trapsfrom June to October. Peak activity density of H. pensylvanicus occurred at the onset of giant foxtail seed shedin both years; however, giant foxtail seed shed peaked approximately 30 to50 d after H. pensylvanicus activity density. Futureresearch should focus on management practices that enhance and support H. pensylvanicus populations later in the growing seasonto maximize suppression of giant foxtail and other weeds that shed palatableseeds later in the season.
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Current address: Department of Crop and Soil Sciences, 515 Bradfield Hall, Cornell University, Ithaca, NY 14853.
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