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United States Department of Agriculture

Agricultural Research Service


item O'neill, Kevin
item Kemp, William - Bill
item Seibert, Catherine
item Rolston, Marni
item Bess, James
item Philips, T

Submitted to: Western North American Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2000
Publication Date: 5/31/2001
Citation: O'Neill, K.M., Kemp, W.P., Seibert, C., Rolston, M.G., Bess, J.A., Philips, T.K. 2001. Natural enemy assemblages on native and reseeded grasslands in southwestern montana: a family-level analysis. Western North American Naturalist. 61:195-203

Interpretive Summary: Careful management of our nation's rangelands requires knowledge about the important insects that live there. Before we can assess any impacts brought about by man's actions, such as livestock grazing or grasshopper control, it is important to know what insects naturally occupy different types of rangeland. In an effort to collect baseline data on important insect predators and parasites on Montana rangelands, we conducted a survey of twenty-six sites which ranged from mountain foothills to lowland prairies. We found that the mixture of insect predator and parasite species was different in mountain foothill versus lowland prairie rangeland plant communities. We also found differences in insect predator and parasite species in adjacent native versus replanted rangelands in both the mountain foothills and the lowland prairies. Studies such as this one will allow us to detect changes in the health of these important rangelands that result from current management activities.

Technical Abstract: In 1988 and 1989, we used sweep sampling to survey families of predatory and parasitoid insects on 26 rangeland sites, some of which had native vegetation (i.e., Stipa comata/Bouteloua gracilis and Festuca idahoensis/Agropyron spicatum habitat types) and others of which had been reseeded to mixtures of exotic grasses (either agropyron spicatum or Bromus inermis) and alfalfa (Medicago sativa) as part of rangeland management programs. The five most abundant families collected, Encyrtidae, Braconidae, Lygaeidae, Nabidae, and Coccinellidae, made up 67 percent of all the predatory and parasitoid insects counted. In quantitative comparisons of plant communities, we found no differences in overall abundance of insect predators and parasitoids in the 51 families surveyed. However, we did find evidence for differences among plant communities in family diversity and evenness, in the relative abundance ranking of the families, and in the abundances of certain families. However, among the seven families for which significant differences in abundance were found in comparisons of native and exotic communities, only the Pteromalidae exhibited significant differences in both years (i.e., in FEID/AGSP versus BRIN/MESA). We also found a significant correlation between the total number of individuals collected for each family of Hymenoptera and the number of known species of each family in North America. The results suggest that even those plant communities that are in close proximity to one another and that occupy identical abiotic zones may exhibit differences in their insect families, particularly Lygaeidae, Torymidae, and Encyrtidae, exhibited temporal trends in abundance between years.

Last Modified: 08/17/2017
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