Theses and Dissertations at Montana State University (MSU)

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Environmental drivers of bee community diversity in Yellowstone National Park
(Montana State University - Bozeman, College of Letters & Science, 2022) Switzer, Kristen Ann; Chairperson, Graduate Committee: Laura Burkle
Pollinators are essential to their ecosystems and facing large declines. Studies on environmental drivers of bee community composition are currently lacking in North America, particularly in national parks. Understanding how bee diversity and plant-bee interactions change across environmental gradients gives us insight into the resilience of bee communities in the future. We collected data at seven sites across an elevational gradient in Yellowstone National Park. Pan traps were used to collect bee diversity data from in 2010, 2011, 2012, and 2020, and hand-netting was used to collect plant-bee interaction data from June to August 2020. We hypothesized that elevation would be a major driver of bee abundance, species richness, and community composition and that bee diversity would decrease as elevation increased. We predicted bee diversity would peak in the middle of the growing season in response to floral diversity peaking at that time. Finally, we predicted plant-bee interactions would be more generalized at higher elevations and flower species richness would be a major driver of network specialization (H2'). Our results revealed that seasonality and elevation were major drivers of bee abundance and species richness, indicating that both spatial and temporal factors are important in driving bee community patterns. Bee species richness was highest in 2010 and declined over years, which may signal that changing environmental conditions are stressing bee communities. Bee abundance and species richness declined as each growing season progressed, which aligns with broader literature on various taxa and mirrors seasonal flower diversity patterns. Despite close alignment between bee and floral diversity patterns, flower species richness was only a significant driver of bee community composition, indicating that other environmental gradients were bigger drivers of bee abundance and species richness patterns. Bee species richness was a significant driver of plant-bee network specialization and elevation, slope, and flower species richness were marginally significant, suggesting that plant- bee interactions are influenced more by spatial than temporal variables. Additional studies focusing on bee diversity across growing seasons and years could provide insights into how changing environmental conditions in the future may influence bee diversity and community resilience in Yellowstone National Park.
The Megachile (Hymenoptera: Megachilidae) of Montana and checklist of bees (Hymenoptera: Apoidea) from the southern Wolf Mountains, Montana and Wyoming
(Montana State University - Bozeman, College of Agriculture, 2021) Pritchard, Zoe Anne; Chairperson, Graduate Committee: Michael A. Ivie
Wild bees are a diverse group of important pollinators, yet several aspects of their biology remain understudied. In particular, baseline data on the diversity and geographic ranges of wild bees is not available for much of Montana. These baseline faunistic data are the first step to understanding the regional biodiversity of bees and to eventually assess their conservation status. We conducted faunal surveys of the genus Megachile in Montana and the bees of the southern Wolf Mountains. Specimens from collecting trips in 2019-2020, historic museum specimens, research collections, and published data records comprise the foundation for the inventory of Montana's Megachile species. We documented 35 species of Megachile in Montana based on 4,968 specimens and present an illustrated identification key and county distribution maps. In the Wolf Mountains, we documented 138 bee species from 4,996 specimens collected on trips in 2019-2020 in Montana and Wyoming. These two studies contribute eight new state records and add important data to the growing list of bee species in Montana.
Honey bee antiviral defense mechanisms at the individual and cellular level
(Montana State University - Bozeman, College of Agriculture, 2021) Parekh, Fenali Mukesh; Chairperson, Graduate Committee: Michelle Flenniken; Katie F. Daughenbaugh and Michelle L. Flenniken were co-authors of the article, 'Chemical stimulants and stressors impact the outcome of virus infection and immune gene expression in honey bees (Apis mellifera)' in the journal 'Frontiers in immunology' which is contained within this dissertation.; Alexander J. McMenamin was an author and Verana Lawrence and Michelle L. Flennikenwas were co-authors of the article, 'Investigating virus-host interactions in cultured primary honey bee cells' in the journal 'Insects' which is contained within this dissertation.; Katie F. Daughenbaugh and Michelle L. Flenniken were co-authors of the article, 'Honey bee antiviral response to flock house virus infection' which is contained within this dissertation.; This dissertation contains an article of which Fenali Mukesh Parekh is not the main author.
Honey bees are important pollinators of fruit, nut, and vegetable crops that constitute a large proportion of the human diet. Unfortunately, annual honey bee colony losses are high, averaging 38% from 2008-2018 in the United States. Honey bee colony losses are attributed to multiple factors, including pathogens and chemical exposure. Virus incidence and abundance have been associated with colony losses. The majority of honey bee viruses are positive-sense single stranded RNA viruses. Honey bees antiviral defense include RNA interference (RNAi), a double-stranded RNA (dsRNA) triggered sequence-specific post-transcriptional silencing mechanism and a non-sequence specific dsRNA-triggered pathway. In addition, signal transduction cascades include the Toll, Imd, and Jak/STAT pathways that promote the expression of honey bee immune response genes that are also induced in response to virus infections. To investigate the impact of chemical exposure on honey bee immune responses and virus infections, we infected bees with a panel of viruses including two model viruses (i.e., Flock House virus (FHV) and Sindbis-GFP) and a naturally infecting honey bee virus, deformed wing virus (DWV) and fed them sucrose syrup containing either thyme oil, a beekeeper applied fungicide Fumagilin-B ®, or the insecticide clothianidin. We determined that bees fed thyme oil augmented sucrose syrup exhibited greater expression of key immune genes, i.e., ago2, dcr-like, abaecin, hymenoptaecin, and vitellogenin and reduced virus abundance compared to virus-infected bees fed sucrose syrup. Whereas, virus-infected honey bees fed diets containing fumagillin or clothianidin exhibited reduced expression of key immune genes and higher virus abundance suggesting that chemical stressors act as immunosuppressors in honey bees. To understand the interplay of viruses and host cell gene expression more precisely, we cultured primary honey bee cells derived from larvae (i.e., hemocytes, immune cells) or pupae (i.e., mixed cell population including epithelial cells, adipocytes, muscle cells, hemocytes) and demonstrated that these cells supported replication of sacbrood virus, DWV, and FHV. Expression of select immune genes, including bap1, ago2, and dcr-like, in virus-infected honey bee cells was similar to expression in individual bees and varied for each virus. Together, these data further our understanding of the honey bee antiviral defense network and provide new tools for studying honey bee host-virus interactions.
The effects of climate-warming on solitary bees and their interactions with plants
(Montana State University - Bozeman, College of Letters & Science, 2019) Slominski, Anthony Hayden; Chairperson, Graduate Committee: Laura Burkle and Jia Hu (co-chair)
The ecological consequences of anthropogenic climate-warming remain poorly understood for pollinators. In order to better understand these consequences, and thus the consequences of climate-warming for pollination services, we must determine how pollinator life histories mediate responses to climate-warming. To help address these research needs, we conducted three studies. First, we used field-collected solitary bee species (i.e., Osmia spp. and Megachile spp.) to investigate how overwintering life stage (i.e., adult versus prepupae), body size, and sex influenced solitary bee survival, weight loss prior to emerging, and timing of emergence in response to manipulated seasonal temperature and the durations of seasons. Second, we manipulated the amount of asynchrony (days) between female solitary bee emergence and flowering periods. We used a mesocosm-based experimental design to investigate the effects of phenological asynchrony on the female lifespan, female interaction rates with flowers, and reproductive success. In a third study, we manipulated the amount of phenological difference between conspecific male and female solitary bees (i.e., the degree of protandry; males emerging prior to females), and investigated the influence of sex-specific phenological responses to temperature on male-female interactions and reproductive success. Our main findings and subsequent conclusions were that i) compared to bees that overwinter as prepupae, patterns in weight loss prior to emergence, adult longevity, and timing of emergence suggested that post-emergence fitness in adult-wintering bees may decrease under climate-warming as a result of increased energy depletion at the time of emergence, increasing asynchrony with flowering periods, and sex-specific phenological responses, ii) asynchrony between a spring-active female solitary bee species (i.e., Osmia cornifrons) and flowering periods caused reductions in offspring body size and reduced interaction rates between females and flowers, which could have consequences for both bee and plant reproductive success, and iii) when the degree of protandry was either reduced or increased from an intermediate level, the probability of female offspring production tended to decrease. This suggests that changes in the degree of protandry may influence the fitness tradeoffs associated with protandry, resulting in consequences for current and future solitary bee reproductive success.
Understanding the effects of wildfire on the functional traits of plants and bees
(Montana State University - Bozeman, College of Letters & Science, 2018) Durney, Janice Simone; Chairperson, Graduate Committee: Laura Burkle
Diversity, often assessed by species richness, fosters ecosystem success, promoting ecosystem services, stability, and adaptation. Evaluations of functional trait composition are a better indicator of ecological process dynamics. Functional trait variation of species within a community (i.e., inter-specific variation) and of individuals within a species (i.e., intra-specific variation) may reflect adaptations and phenotypic variation contributing to the functional diversity of a community in the face of change. Wildfires have shifted from mixed-severity to frequent high-severity fires, due to fire suppression and climate change, modifying ecosystem function, trait selection pressure, and species sorting. Traits involved in plant-pollinator interactions can be used to understand the mechanisms underlying shifting interactions across communities and how post-wildfire environmental conditions affect community assembly, structure, and stability. We tested how productivity, time-since-burn, and wildfire severity influenced mean functional trait values and inter- and intra-specific functional trait variation of plants and bees known to interact in southwestern Montana, USA. Fieldwork was conducted from 2013-2017 in two locations that differed in productivity with similar fire histories of recent-mixed-severity, recent-high-severity, older-high-severity burns, and unburned areas. Functional traits involved in plant-bee interactions were selected and measured among plant and bee species observed across these various productivity, time-since-burn, and fire severity levels. We found that as productivity and time-since-burn increased, the mean functional trait values and inter- and intra-specific functional trait variation of plants and bees increased. In addition, productivity, time-since-burn, and fire severity affected the functional trait values and variation of plant species more than bee species. These results suggest that as productivity and time-since-burn increases so does trait diversity - promoting ecosystem function and stability. The increased effect of productivity and time-since-burn on plant functional traits compared to bee traits suggests the dispersal abilities of bees allow them to cope with the effects of fire, while plant species are more prone to productivity and time-since-burn habitat filtering and species sorting, potentially due to limited mobility. Our results support previous findings that shifting wildfire regimes from mixed to high-severity burns increases species sorting and limits trait variation after wildfire regardless of productivity but trait variation increases as time-since-burn and productivity increases.
Impacts of dryland farming systems on biodiversity, plant-insect interactions, and ecosystem services
(Montana State University - Bozeman, College of Agriculture, 2018) Adhikari, Subodh; Chairperson, Graduate Committee: Fabian D. Menalled; Laura Burkle (co-chair)
Farming system impacts the structure and functioning of associated biodiversity and plant-insect interactions. However, the extent of these impacts is largely unknown in drylands of the Northern Great Plains, an important region for cereal, pulse, oilseed, and forage production. Using three complementary studies, I compared the impacts of conventional and organic systems on associated biodiversity (weeds, bees, insect pests, and parasitoids), bee-flower networks, and bumblebee colony success. First, I assessed stem cuts by and parasitism on Cephus cinctus (wheat stem sawfly) in spring and winter wheat cultivars grown in conventional and organic fields. I found that organic fields had less C. cinctus infestation and more braconid parasitoids of C. cinctus, indicating an increased pest regulation in organic system. I compared C. cinctus preference and survival on Kamut with Gunnison and Reeder wheat cultivars and found the lowest C. cinctus oviposition and survival in Kamut, suggesting that Kamut is a potential genetic source for this pest. Second, I assessed the impacts of conventional and organic systems on forb and bee communities. I found greater forb diversity and more connected bee-flower networks in organic fields, but bee communities did not differ between systems. Comprising only 12% of the landscape, natural habitat did not affect small-bodied bees in either system but had a positive effect on large-bodied bees at the scale of 2000 m radius. These results indicate that an increased forb diversity and bee-flower interaction in organic fields is not enough to offset the negative effects of landscape homogeneity on bees. Third, I compared Bombus impatiens colony success, worker condition, and colony-collected pollen between farming systems. I found greater growth rate, brood cells, and pollen species richness in B. impatiens colonies as well as lower wing wear and greater body lipid mass in workers from organic fields, than in conventional fields. The greater colony success and better worker conditions could be a proxy for better ecosystem services provided by organic fields. Overall, my studies show that organic farming supports greater associated biodiversity, more complex bee-flower networks, and better biodiversity-based ecosystem services in the Northern Great Plains.
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.
Insect microbe interactions: honey bee antiviral defense mechanisms and characterization of Spiroplasma colonizing wheat stem sawfly
(Montana State University - Bozeman, College of Agriculture, 2017) Brutscher, Laura Marie; Chairperson, Graduate Committee: Michelle Flenniken; Katie F. Daughenbaugh and Michelle L. Flenniken were co-authors of the article, 'Virus and DSRNA-triggered transcriptional responses reveal key components of honey bee antiviral defense' in the journal 'Scientific reports' which is contained within this thesis.; Curtis Fowler, David K. Weaver and Carl J. Yeoman were co-authors of the article, 'Identification and characterization of a Spiroplasma sp. (Ixodetis clade) associated with the wheat stem sawfly (Cephus cinctus)' submitted to the journal 'Microbial ecology' which is contained within this thesis.
Insects play important roles in ecosystems throughout the world. There are many beneficial insects, including those that pollinate plants in diverse landscapes, while other insects are considered agricultural pests. Regardless of ecological role, insects are hosts for microbial symbionts and pathogens. Some microorganisms (e.g., viruses) are harmful to insect health, but many microbial symbionts aid in host biological processes. The projects herein describe the interplay between insects and microbes; specifically (1) honey bee host - virus interactions and (2) identification and characterization of a wheat stem sawfly-associated Spiroplasma. Honey bees (Apis mellifera) are pollinators of numerous agricultural crops and other plant species. Since 2006, there have been high annual losses of honey bee colonies in the U.S. (~33%) and throughout the world. Colony deaths are influenced by multiple factors including RNA virus infections. Honey bee antiviral defense involves several immune pathways, including dsRNA mediated responses, (i.e., RNA interference and non-sequence-specific dsRNA-triggered responses), but their relative importance in antiviral defense is not well understood. To investigate honey bee antiviral defense, bees were infected with model virus in the absence or presence of dsRNA, which reduced virus abundance. Transcriptome-level analysis determined hundreds of genes were differentially expressed in response to co-treatment of dsRNA and virus, including immune-related genes. RNAi-mediated gene knockdown of two putative antiviral genes increased virus abundance and supported their antiviral role. Additional investigation of these and other genes will improve our understanding of dsRNA-mediated antiviral defense in honey bees. In contrast, wheat stem sawflies (Cephus cintus) are major wheat pests in the Northwest United States. Strategies that target endosymbionts of sawflies could reduce wheat crop losses. Hereunto, the microbes that colonize wheat stem sawfly have not been explored. Targeted DNA sequencing determined sawflies were colonized by a Spiroplasma species that has greatest 16S rRNA sequence identity with Ixodetis clade species. Metagenomic sequencing identified several Spiroplasma encoded genes involved in metabolism, which may be important to the sawfly host. Further characterization of honey bee-virus interactions and the role of Spiroplasma in sawfly health may contribute to limiting threats to global crop production and will further scientific understanding of non-model insect-microbe interactions.
Evaluating the effects of climate change and pathogens on pollinator health using plant functional traits and longitudinal monitoring
(Montana State University - Bozeman, College of Letters & Science, 2017) Glenny, William Robb; Chairperson, Graduate Committee: Laura Burkle; Michelle Flenniken (co-chair)
Pollinators are essential for the maintenance of biodiversity, ecosystem function, and economic productivity. In particular, bee pollinators are required for plant reproduction and pollination of agricultural crops. However, land use change, climate change, pathogens, pesticide exposure, among other factors likely act alone and in combination to negatively impact bee pollinators and the services they provide. Further resolution of the effects of these stressors, both individually and combined, on bee pollinators is important to understand the global decline of pollinator health. Abiotic conditions associated with climate change may alter plant traits important for pollinator attraction leading to in shifts in plant-pollinator communities. Floral visual and chemical traits were measured in four species of forbs subjected to elevated or ambient concentrations of carbon dioxide, and decreased or normal water availability in a fully factorial crossed design. Treated plants were observed for pollinator visitation rates and community composition to better understand the mechanisms by which climate change can influence pollinator attraction. Results indicate that changes in both visual and chemical cues of plants will alter plant-pollinator interactions. Furthermore, plant functional trait responses to climate change increase competition for pollinators in forbs with overlapping flower types, while facilitating pollinator visitation to forbs with dissimilar flower types. Pathogens contribute to annual honey bee colony losses and the declining populations of some wild bee species. Bee pathogens, including viruses, fungi, microparasites and ectoparasites, can vary across geographic location and season. To examine the impact of pathogens on honey bee colony health, using colony size as a proxy for health, we longitudinally monitored pathogen prevalence and abundance of pathogens in honey bee colonies involved in California almond pollination. Individual honey bee associated pathogens varied throughout the one year monitoring period, but Deformed wing virus in parallel with increasing levels of Varroa destructor mite infestation predominated shifts in honey bee pathogen profiles by the end of the sampling period. Our results indicate that bee populations experience multiple concurrent threats operating at multiple scales to affect pollinator health. Continued investigation into factors affecting pollinator health both independently and in concert are needed to develop strategies mitigating declines in pollination services.
Plant-pollinator network assembly after wildfire
(Montana State University - Bozeman, College of Letters & Science, 2018) Simanonok, Michael Peter; Chairperson, Graduate Committee: Laura Burkle
Plant-pollinator networks are threatened by anthropogenic influence due to habitat loss, changing fire regimes, climate change and other factors. Furthermore, we have little current knowledge for how species interactions and processes like pollination assemble and recover post-disturbance. Studying the mechanisms by which plant-pollinator interactions assemble in a post-disturbance landscape, particularly across gradients of disturbance intensity and successional time, would greatly help in building foundational ecological knowledge regarding the assembly of species interactions as well as provide specific information to aid conservation and management. Therefore, we investigated plant-pollinator network assembly after wildfire, between mixed- and high-severity burns and across time-since-burn, and we asked i) how do network structure and the network roles of persistent species vary ii) how does wildfire change the nutritional landscape of available floral pollen quality and how does that influence bumble bee foraging and nutrition, and iii) how do nesting and floral resources affected by wildfire influence wood-cavity-bee nesting success and richness? Our study design involved four wildfires from the Absaroka Mountains of southwest Montana, USA, which included a range of burn severities as well as a 1-25 year chronosequence of time-since-burn sampled primarily from 2014 to 2016. Bees were sampled via hand netting and nesting boxes alongside floral census transects and pollen sampling to assess metrics important to plant-pollinator network assembly, available floral pollen quality, bumble bee nutrition, and wood-cavity-nesting bee nesting success. The primary findings are that i) plant-pollinator network structure does not dramatically shift with burn severity or time-since-burn, nor do the network roles of persistent species, ii) available floral pollen quality and bumblebee nutrition are limited by high-severity burns, and iii) burn severity has little effect on the nesting success of wood-cavity-nesting bees. The conclusions that follow these results are mainly that i) evidence of constant structure and low variance of species' roles provides evidence for preferential attachment over opportunistic attachment in assembling plant-pollinator networks post-disturbance, ii) varied species composition between mixed- and high-severity burns may mean that bumble bees are nutritionally limited in high-severity burns, and iii) nesting resources do not appear to strongly limit nesting success or richness of wood-cavity-nesting bees.

Theses and Dissertations at Montana State University (MSU)

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