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Item Effects of alternative management practices on the abundance of arthropods in a mixed-crop agroecosystem(Montana State University - Bozeman, College of Agriculture, 2013) Gill, Paramjit Singh; Chairperson, Graduate Committee: Kevin O'NeillWe evaluated the effects of alternative management practices on the abundance and diversity of arthropods in a mixed-crop agroecosystem in studies conducted in 2010 and 2011 at the Fort Ellis Experimental Station near Bozeman, MT. In one study, we quantified arthropod relative abundance in plots across three summer fallow weed management practices (sheep grazing, mechanical/tillage, and chemical herbicide) incorporated into a three-year rotation in two different sets of crops. Arthropod abundance was compared among 1) the spring wheat plots under the three management schemes with the rotational treatments (continuous spring wheat and rotational spring wheat), 2) the pea/hay barley plots under the different weed management schemes, and 3) fallow plots under the three weed management schemes. In a second study, we examined arthropod relative abundance in plots with alternative alfalfa cultivars (Cimarron SR, HayGrazer, and Shaw). Sweep net samples were taken to compare the abundances of the most common insect orders and families (as well as a few abundant species and genera). In addition, baited traps were used to compare the abundance of click beetle larvae or wireworms (Coleoptera: Elateridae) within the different management schemes and treatments. This study demonstrated that the number of arthropods in the continuous spring wheat was lower compared to the rotational spring wheat. Arthropod abundance in the pea/hay barley plots under the three different managements was inconsistent from one year to the other. In the summer fallow plots, abundance of most arthropod taxa was the lowest in the mechanically-treated plots, whereas there was no difference in the number of most arthropods present between the chemical and grazed plots which shows that sheep grazing was equally effective as the application of herbicides in reducing arthropod numbers on summer fallow plots. The abundance of most arthropod taxa did not differ among the Cimarron SR, HayGrazer, and Shaw alfalfa cultivars except for Aphididae, Formicidae, and Ichneumonidae in 2010. Nine species of wireworms were collected from the study site with Aeolus mellilus Say being the most common. In both years, A. mellilus was most abundant in the continuous spring wheat plots compared to the other plots.