Theses and Dissertations at Montana State University (MSU)
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Item Tritrophic responses to signaling formulations sprayed in wheat stem sawfly-infested field plots(Montana State University - Bozeman, College of Agriculture, 2019) Caron, Christopher G.; Chairperson, Graduate Committee: Scott PowellThe wheat stem sawfly (Cephus cinctus Norton) is an economically important pest of wheat in the Northern Great Plains of North America. Producers and researchers are continuing to search for an effective management strategy. A combination of management tactics, such as host-plant resistance and biocontrol, may be the best method to suppress wheat stem sawfly (WSS) populations. My study examines whether direct toxicity, induced host-plant resistance, or the manipulation of tritrophic interactions, can be achieved through the application of signaling molecules in WSS-infested plots. The overall objective was to assess whether signaling molecules could be incorporated as a management tactic for WSS. Field experiments assessed whether aqueous applications of methyl jasmonate (MeJA), methyl salicylate (MeSA), and Actigard? influence WSS fitness, host-plant fitness, or the recruitment of natural enemies. Treatments were applied in WSS-infested plots for 3 consecutive weeks in both 2017 and in a second experiment in 2018. Wheat samples were collected before harvest and processed to assess parameters of infestation and parasitism. Plant growth and yield parameters were also recorded. The field trials suggested that MeJA and Actigard? induced significant changes that can impact tritrophic interactions in winter wheat. No effect was observed from the applications of MeSA. WSS fitness parameters decreased with applications of MeJA. MeJA treated plots had decreased infestation (2017), decreased larval weight (2018), and increased neonate mortality (2018). Actigard? treated plots had decreased larval weight and increased recruitment of clerid beetles (Phyllobaenus dubius Wolcott) (2017). Treatments of MeJA decreased stem height and grain weight, while treatments of Actigard? decreased grain weight in 2017. Although many of these findings were not consistent for both growing seasons, this study demonstrates the potential for these signaling molecules to manipulate the interactions between the WSS, or its host plant, and associated natural enemies in winter wheat.Item The effect of osmotic stress on growth characteristics of two spring wheat varieties(Montana State University - Bozeman, College of Agriculture, 1961) Richardson, GlennItem Influence of native bunchgrass and invasive forb litter on plant growth in a semi-arid bunchgrass prairie(Montana State University - Bozeman, College of Agriculture, 2006) Hoopes, Carla; Chairperson, Graduate Committee: Cliff Montagne.Litter can influence plant species diversity. I investigated plant litter effects for density, cover, and biomass on common St. Johnswort Hypericum perforatum L., a nonnative- species-group, and a native-species-group. The following hypotheses were tested: litter source would favor species dominant in the litter; the high amount of litter (908 grams) would decrease density more than the moderate amount (454 grams); coarse size litter would decrease density more than fine size; and the effect of litter would depend upon interactions of all three variables. Above-ground plant material was removed from two adjacent sites, one a native bunchgrass prairie (native site), the other infested with St. Johnswort (invasive site). Three-way litter treatments were applied in October 1999 and reapplied in July 2000 in combinations of high- or moderate-amount of litter, native or St. Johnswort species by source, and fine or coarse texture by size. Sampling occurred at peak standing crop July 2000 and 2001. Analysis of variance in 2001 data results follow. St. Johnswort was decreased by its own litter (all P <.06). St. Johnswort and native species were detrimentally influenced more by the high amount of litter than by the moderate amount (all P <.05). Although litter size did not influence St. Johnswort, native species biomass was more detrimentally influenced by coarse size litter than by fine (P <.05). When we added more fine size litter, native species were more detrimentally influenced than when we increased the amount of coarse litter (P <.06). In the invasive site, moderate amounts of coarse native litter decreased St. Johnswort. High amounts of coarse St. Johnswort litter decreased it even more (both P <.05). The opposite effects were found for native species (both P <.05). In the native site, the only treatment that reduced St. Johnswort more than no litter was the high amount of fine St. Johnswort litter (P <.05). The same fine St. Johnswort litter in moderate amounts was the only treatment that did not decrease native species (P <.05). The complexity of litter influence through interactions of amount, source, and size detrimentally and non-detrimentally caused changes to plant species diversity at each site (all P <.05).Item The impacts of a stem boring weevil, Mecinus janthinus, on dalmatian toadflax, Linaria dalmatica(Montana State University - Bozeman, College of Agriculture, 2008) Schat, Marjolein; Chairperson, Graduate Committee: Robert K. D. Peterson; Fabian D. Menalled (co-chair)Classical biological control of weeds is generally considered an effective, safe, and cost effective tool for controlling widespread weeds in natural areas. However, only 60% of releases have become established and, of those, only 50% have led to control. Therefore, understanding the impacts of agents on target weeds across spatial scales, at different insect densities, and over time can give biological control practitioners the knowledge necessary to improve establishment and success rates. My studies characterized the impacts the biological control agent, Mecinus janthinus, on the rangeland weed Dalmatian toadflax (Linaria dalmatica) at individual plant and plant population scales. Individual plant studies were conducted in a garden and replicated on plants growing in the field, to measure the impact of agents on plant growth and primary physiology. The population study followed operational scale releases of M. janthinus for three to four years using intensive monitoring to characterize L. dalmatica cover, density, and population structure, and weevil establishment and population increase. I also evaluated which parameters were most important to measure to determine establishment and success. In the common garden experiment, M. janthinus injury was found to reduce relative plant growth, as well as root, stem, and reproductive biomass at medium and high adult densities. Trends of reduced photosynthetic, conductance, or transpiration rates with increasing M. janthinus density were observed. In the field experiment, M. janthinus injury led to reduced growth. Gas exchange rates decreased over the season and were lower in plants exposed to high larval and adult herbivore pressure. Field monitoring indicated successful M. janthinus establishment at releases across a range of elevations, slopes, and geographic locations, though high rates of overwintering mortality were observed at all sites. Linaria dalmatica cover was variable within watersheds and patches, and also differed between watersheds. Abundance of L. dalmatica decreased over time based on cover measurements, but did not change over time with respect to density. The proportion of mature L. dalmatica stems decreased over time. The majority of changes in L. dalmatica over time were the same in release and control transects and could not be attributed to M. janthinus.Item Long-term perspectives on northern Rockies climatic variability from tree rings in Glacier National Park, Montana(Montana State University - Bozeman, College of Agriculture, 2004) Pederson, Gregory Thomas; Chairperson, Graduate Committee: Lisa J. Graumlich.Instrumental climate records reveal fluctuations in summer moisture anomalies and winter snowpack in Glacier National Park, Montana, on decadal and multidecadal timescales. However, because climate records for the region are limited to the 20th century, studies on the impacts of long-duration variations in climate on physical and ecosystem processes were limited. Therefore, a reconstruction of summer moisture variability (June - August) spanning A.D. 1540-2000 was created from a multi-species network of tree-ring chronologies sampled in Glacier National Park. The reconstruction shows decadal-scale shifts between drought and pluvial events with a pronounced cool/wet period spanning the end of the Little Ice Age (A.D. 1770-1840). The single most exceptional drought event occurred over the 20th century (A.D. 1917-1941) and was associated with the most spatially consistent drought regime throughout the northern Rockies and Pacific Northwest over the past ~500 yrs. Among a wider spatial network of hydroclimatic reconstructions arrayed along a north-south Rocky Mountain transect, trends at Glacier National Park were found to be most similar to those in the Canadian Rockies and the Pacific Northwest.