Scholarship & Research
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Item Mortality dynamics and life tables of Megachile rotundata(Montana State University - Bozeman, College of Agriculture, 2019) Donahoo, Claire Katherine; Chairperson, Graduate Committee: Robert K. D. Peterson.; Kevin M. O'Neill, Casey M. Delphia and Robert K. D. Peterson were co-authors of the article, 'Mortality dynamics and life tables of the alfalfa leafcutting bee, Megachile rotundata (Hymenoptera: Megachilidae)' which is contained within this thesis.The alfalfa leafcutting bee, Megachile rotundata (F.), contributes to the pollination of more than two-thirds of alfalfa seed production in North America. However, population losses of more than 50% are common in the U.S., requiring many alfalfa seed producers to import costly bees from Canada. Understanding the mortality dynamics of M. rotundata and being able to estimate these impacts on their populations are critical for identifying ways to conserve and increase their populations. Therefore, this study had three objectives: 1) identify mortality classes for M. rotundata in brood cells; 2) experimentally manipulate parasitism and temperature to determine their impact on total mortality; and 3) estimate mortality risks using the multiple-decrement life table (M-DEC). Research was conducted over two years on a 38.5 ha alfalfa field in Toston, MT. Nest shelters were manipulated for a main temperature treatment (low vs. high) and a sub-treatment for parasitism (backing-present vs. backing-absent). Females constructed and provisioned nests during the summer and offspring mortality was assessed during the summer and the following fall. Mortality classes were then analyzed using the M-DEC model. We found no temperature-treatment effect, so our main treatment was not used in the analyses. However, for every 1 °C increase in nest-tunnel temperature, there was a 7% increase in total mortality. Nest boxes without felt backing (backing-absent) had a 43% increase in mortality over both years compared to those with felt (backing-present). Average temperature decreased by 4.4 °C from 2017 to 2018, while average relative humidity increased by 12.1%. Total mortality was approximately 15% for both years, but the proportion of each mortality class differed substantially, with death by parasitoids greatest in 2017 and death by pollen ball greatest in 2018. Mortality from each class was highly irreplaceable in that it is unlikely to be replaced by another class, and death by predation was the only cause with similar mortality between the two years. The ability to identify and quantify mortality classes and their respective irreplaceable mortality, especially for parasitoids, pollen ball, and predators, will help producers maintain and increase bee populations.Item Multi-trophic level interactions between the invasive plant Centaurea stoebe, insects and native plants(Montana State University - Bozeman, College of Agriculture, 2014) Herron-Sweet, Christina Rachel; Chairperson, Graduate Committee: Jane M. MangoldCentaurea stoebe is one of the most common and problematic invasive plants in the western United States and Canada. To fully comprehend C. stoebe's impact on native organisms and enhance methods for its control, we must come to a better understanding of how it integrates into the ecological networks of its introduced range. My research objectives addressed this need by assessing (1) how pollinator communities vary with C. stoebe density, (2) the impact of C. stoebe invasion on pollinator visitation to and reproduction of the native plant Heterotheca villosa, and (3) the extent to which C. stoebe biological control agents are attacked by native parasitoids. Objective 1 was completed during summer 2012 at nine C. stoebe infested sites in western Montana. Each site was visited once per week from June to August to document plant-pollinator interactions. Differences in pollinator abundance, richness, and community composition were found across varying C. stoebe densities, but differences depended on the time of season. Prior to C. stoebe blooming, plots without C. stoebe were visited by a higher abundance and richness of pollinators than plots with high C. stoebe density. The opposite pattern was observed during peak C. stoebe bloom. Objective 2 was completed during summer 2013 at a site near Bozeman, Montana. Potted C. stoebe plants were placed at densities of 1, 2, or 4 plants next to naturally occurring H. villosa plants to assess effects on pollinator visitation to and reproductive output of H. villosa. Centaurea stoebe, at the densities used, had no effect on the visitation to or reproduction of H. villosa. For objective 3, throughout 2012 and 2013, 19 and 45 sites were visited to make C. stoebe root and seedhead collections, respectively. Collections were then monitored for biological control agent and parasitoid emergence in the laboratory. Nine parasitoid species (four of which were not previously known to be associated with C. stoebe) emerged along with ten biological control agent species. Host-parasitoid associations were verified for three of the nine parasitoid species: Urophora affinis - Pronotalia carlinarum, Larinus spp. - Scambus brevicornis, and Agapeta zoegana - Bracon sp.Item Pollinators of slender white prairieclover(Montana State University - Bozeman, College of Agriculture, 2008) Pearce, April Marie; Chairperson, Graduate Committee: Kevin O'Neill; Sue Blodgett (co-chair)Slender white prairieclover (Dalea candida) is a perennial angiosperm, grown at Bridger plant materials center (BMPC) for reclamation purposes. Interest in the pollinators and pests of this plant developed at BPMC following the death of a 5year old stand. The objectives of these experiments were to (1) determine the diversity and identify the potential pollinators on D. candida and other cultivated and non-cultivated angiosperm species using sweep samples and pan traps; (2) determination of pollen load size and composition of individual insects collected on angiosperm plant species; (3) use of different size exclusion cages to determine the general sizes of insects most important for pollination of D. candida at BPMC; and (4) determine the composition of the community of cavity-nesting Hymenoptera species at BPMC by using trap nests. The overall diversity of BPMC was much higher than expected in a monoculture agriculture area, with a total of 102 Hymenoptera taxa collected. Hill's #2 index was used to determine the diversity of different angiosperm plants and revealed that D. candida had the highest diversity. Analysis of pollen loads via the proportion of "pure" vs. mixed loads (PBP) and mean proportion of conspecific pollen (PCP) revealed conflicting results between the two measures, but there does appear to be some floral constancy occurring, especially in D. candida. Kruskal-Wallis tests of differences in exclusion cage treatments revealed that there are differences in pollination efficacy and the size subset allowed to reach the flowers. Emergences from trap nests revealed differences in the trap nesting community at BPMC and actual pollinator collections in the field.