Date of Award:

5-1-1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Life Sciences:Biology

Committee Chair(s)

James A. MacMahon

Committee

James A. MacMahon

Committee

Brien E. Norton

Committee

B. Austin Haws

Committee

Ivan G. Palmblad

Abstract

Arthropod faunas in different types of reseeded rangeland vegetation were studied in 1980 and 1981, with an emphasis on sap-feeders and predators. Manipulations of grass density and sagebrush presence/absence were performed in 1981 to assess the relative effects of these 2 factors in producing the observed arthropod faunas. Major sap-feeders of crested wheatgrass (Ayropyron cristatum L.) were Irbisia brachycera (Uhler) and Conostethus americanus (Knight) (Miridae), and Oikraneura carneola (Stal) (Cicadellidae). The major sap-feeder of tall wheatgrass (Thinopyrum panticum (Podp.) Barkworth & Dewey) was Laccocera obesa Van Duzee (Delphacidae). I. brachycera, C. americanus, and L. obesa showed population patterns related to grass phenology. l. brachycera and C. americanus were most abundant in the leaf stages of the grasses, whereas L. obesa was most abundant in the flowering stages. In 1980: (1) The shrub-grass and tree-grass mixtures had lower abundance and biomass, and higher richness and diversity (H'), of sap-feeders, compared to the grass plots; (2) The grass monoculture had the greatest biomass and lowest richness and diversity of sap-feeders of all the plots, and its fauna appeared the earliest; (3) Abundance and richness of predators were greatest in the tree-grass plot, and predator biomass was greatest in the grass biculture; (4) Sap-feeding faunas of crested wheatgrass depended highly on vegetation structure. In 1981: (5) Transplanted grass clumps had a homopteran-dominated fauna with greater predator levels in native areas, low arthropod levels in the reseeded mixtures and a very abundant mirid-dominated fauna with lower predator levels in the reseeded monoculture; (6) Higher grass densities in the manipulations resulted in greater predator abundance, and greater sap-feeder and predator richness and diversity; (7) Grass plants with sagebrush leaves placed around them had lower mirid abundance. The data suggest that the particular combination of shrub and grass density determine the composition of the arthropod sap-feeding fauna. It also appears that, in comparing faunas of crested wheatgrass in pure stands to stands mixed with big sagebrush, the effects of big sagebrush were a more important determinant of faunal structure than the density of crested wheatgrass. Implications for range pest management are discussed.

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