Hymenoptera Parasitoid Response to Sheep Grazing, Tillage, and Herbicides in Wheat-Fallow Rotations

Sweep net sampling of spring and winter wheat (Triticum spp.) was conducted in 2007 and 2008 at the Fort Ellis Research and Extension Center, Montana State University, Bozeman, MT to determine hymenoptera parasitoid family composition, abundance, and diversity in two wheat-fallow cropping systems managed by either tillage, herbicides, or domestic sheep (Ovis aries) grazing. Eleven hymenopteran families classified as parasitoids were captured in 2007 and 16 families in 2008. The mean abundance of parasitoids was greatest (P ≤ 0.05) in crops where the fallow component of the rotation was managed with sheep grazing, as opposed to tillage and herbicide systems. Family diversity, as indexed by Simpson's D, did not differ between fallow management treatments (P = 0.88) or cropping system (P = 0.74) but did differ between study year (P ≤ 0.01).