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Seasonality and alternative floral resources affect reproductive success of the alfalfa leafcutting bee, Megachile rotundata
(Taylor & Francis, 2024-08) Delphia, Casey M.; Burkle, Laura A.; Botti-Anderson, Joshua M.; O'Neill, Kevin M.
Background: Managed populations of the alfalfa leafcutting bee (ALCB), Megachile rotundata (F.), are often not sustainable. In addition to numerous mortality factors that contribute to this, the dense bee populations used to maximize alfalfa pollination quickly deplete floral resources available to bees later in the summer. Providing alternative floral resources as alfalfa declines may help to improve ALCB reproduction. Methods: We examined the relationship between floral resource availability and ALCB reproduction and offspring condition via (1) a field study using alfalfa plots with and without late-blooming wildflower strips to supply food beyond alfalfa bloom, and (2) a field-cage study in which we provided bees with alfalfa, wildflowers, or both as food resources. Results: In the field study, bee cell production closely followed alfalfa floral density with an initial peak followed by large declines prior to wildflower bloom. Few bees visited wildflower strips, whose presence or absence was not associated with any measure of bee reproduction. However, we found that female offspring from cells provisioned earlier in the season, when alfalfa predominated as a source of provisions, eclosed with greater body sizes and proportion body lipids relative to total body mass. For bees restricted to cages, the proportion of offspring that survived to adults was highest on pure alfalfa diets. Adding wildflowers to cages with alfalfa did not affect adult offspring production or female offspring body size and lipid content. Furthermore, although similar numbers of adults were produced on wildflowers alone as with alfalfa alone, females eclosed with smaller body sizes and lower proportion body lipids on wildflowers despite the higher protein content we estimated for wildflower pollen. We found no evidence that adding the late-season wildflower species that we chose to plant enhanced ALCB offspring numbers. Our results highlight the importance of considering multiple measures of reproductive success, including offspring body size and lipid stores, when designing and evaluating floral resource management strategies for agroecosystems.
Pollinator conservation and restoration in semi-natural ecosystems
(Montana State University - Bozeman, College of Letters & Science, 2022) Glenny, William Robb; Chairperson, Graduate Committee: Laura Burkle; This is a manuscript style paper that includes co-authored chapters.
Semi-natural ecosystems are areas with biological and physical characteristics that resemble natural ecosystems but are also affected by anthropogenic disturbances. Semi-natural ecosystems are also areas with high insect pollinator diversity. Land management actions within semi-natural ecosystems may therefore be important to counteract future declines of insect pollinators. However, current restoration strategies for insect pollinator communities are based on evidence from agricultural ecosystems, which have frequent human interventions to ensure plant success, neglect the importance of nesting materials, and primarily benefit generalist species. To inform management actions for the conservation and restoration of insect pollinators in semi- natural ecosystems, I (1) synthesized the current understanding of the effects of common land management actions on insect pollinators on public lands in the US, (2) identified habitat characteristics which structure the taxonomic and functional diversity of bee communities, (3) evaluated the strength of influence of mechanisms associated with diet breadth across groups of bee species and (4) designed a conceptual model which can be used to select flowering plant species to provide food resources for bee communities in semi-natural ecosystems. Management actions that increase the abundance of floral and nesting resources to support bee species from different functional groups are required to conserve and restore insect pollinator communities in semi-natural ecosystems. I found that (1) management actions have positive, neutral, and negative effects on insect pollinators, but research trends vary depending on the taxon and habitat type, (2) the taxonomic and functional diversity of bee communities are structured by the abundance of both floral and nesting resources, (3) patterns of abundance across space and time have a more positive effect on the diet breadth of bumble bee species compared to non- bumble bee species, and (4) wildflower species that receive a high visitation rate and richness, occupy functionally important positions within bee-flower interaction networks, and are spatially and temporally widespread are important to provide bee communities with food resources in semi-natural ecosystems. These wildflower species may be particularly important to include within seed mixes to revegetate semi-natural ecosystems and provide food resources for insect pollinators.
Bee and butterfly communities in roadside habitats: identifying patterns, protecting monarchs, and informing management
(Montana State University - Bozeman, College of Letters & Science, 2023) Meinzen, Thomas Claasen; Chairperson, Graduate Committee: Diane M. Debinski
Insect pollinators play a critical role in our natural and agricultural ecosystems. With global pollinator declines and habitat loss, attention has turned to roadside right-of-way lands (ROWs) as potential areas for supporting pollinator populations. Although many roadsides host flowering plants, understanding whether--and under what circumstances--roadsides actually benefit pollinator populations is critical for good conservation decision-making. Through a literature review, we found that pollinator population data (e.g., birth and death rates) are lacking to assess whether roadsides are a source or sink for pollinator populations. However, conscientious management practices, including reduced, well-timed mowing, selective, targeted spraying, and well-placed native plantings can improve roadsides' potential to support robust pollinator populations. Identifying roadside habitat for diverse pollinator communities and imperiled species is essential to prioritize pollinator-focused management practices across ROW systems. To support efforts to conserve monarch butterflies (Danaus plexippus), we surveyed 1,465 km (910 miles) of southern Idaho highways, mapping 1,363 patches of showy milkweed (Asclepias speciosa), the monarch's host plant. Roadside milkweed often bordered irrigated fields and crops; water availability may best explain its distribution. Existing statewide milkweed models (Svancara et al., 2019) did not effectively predict milkweed distribution in ROWs, suggesting the importance of roadside-specific factors, such as ROW management and disturbance history. To identify patterns of pollinator richness and abundance in Idaho ROWs, we surveyed butterflies and sampled bees at a randomized set of 63 100-meter (328-foot) roadside transects in southeastern Idaho, stratified by highway class and NDVI (greenness) category. Lower NDVI (less green) sites, those with more flowering plant species, and sites along smaller, less-trafficked highways supported significantly more species of bees, while ROWs with more abundant flowers were associated with more species of butterflies. Low NDVI sites were often characterized by native sagebrush plant communities, while sites of high NDVI were associated with high proportions of non-native plants, suggesting that NDVI might be useful both in predicting bee richness and abundance (low values) and locating developing noxious weed patches (high values). These results, together with our management recommendations, can help prioritize ROWs for pollinator protection and increase their capacity to support diverse pollinator communities.
Native pollinators: the effects of livestock grazing on Montana rangelands
(Montana State University - Bozeman, College of Agriculture, 2019) Blanchette, Gabrielle Elizabeth; Chairperson, Graduate Committee: Craig Carr; Michael A. Ivie (co-chair)
Although native pollinators on rangelands serve, in part, as food at higher trophic levels, their primary ecosystem function is pollination. With 70% of western U.S. rangelands grazed by livestock, understanding how grazing affects native pollinators is a key component to managing rangelands, yet it is not well understood. In this study, I investigated how cattle grazing influences both diversity and abundance of native pollinators, including bees and wasps, syrphid flies, butterflies, and moths at two research locations for six to 10 weeks during the spring of 2016, 2017, and 2018. The first site, near Sidney, MT, served to understand if pollinators were more closely associated with active cattle grazing or rested pastures. The second site, near Roundup, MT, served to understand if pollinators were more associated with pastures either enrolled or not enrolled in the Sage Grouse Initiative, or pastures that had not experienced livestock grazing in previous seven years. Colored pan traps were deployed weekly in each treatment at each site. In addition to pollinator collections, weekly measurements of vegetation via Daubenmire frame were also collected. I collected 17,078 specimens at Sidney and 13,683 specimens at Roundup. My results suggest that in drier sagebrush landscapes, native pollinators are positively to neutrally associated with pastures moderately grazed by livestock. However, in mixed grass prairie landscapes that receive high precipitation, rest-rotational grazing does not appear to have a significant effect on primary native pollinators.
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.
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.
The influence of post-wildfire logging on forb and pollinator communities and forb reproductive sucess, Gallatin National Forest, Montana
(Montana State University - Bozeman, College of Letters & Science, 2016) Heil, Laura Jean; Chairperson, Graduate Committee: Laura Burkle
Pollinators are in decline worldwide, and these declines have implications for flowering plants and their reproduction, given that 80% of flowering plants depend on insects for pollination. One potential contributor to pollinator species' declines is shifts in disturbance regimes, such as increased severity and frequency. Wildfires are essential natural disturbances that are important drivers of forest biodiversity in the western U.S., and there is often pressure to respond to wildfire with management including post-wildfire logging. This management strategy involves the removal of dead trees for economic value immediately following wildfire. Thus, is expected that post-wildfire logging has additional impacts on forest communities compared to non-salvage logging, and that it impacts forb and pollinator communities. Several studies have examined the short-term responses of forb and pollinator communities to wildfire and non-salvage logging individually, and one study examined their combined effects. However, no studies have examined the long-term effects of post-wildfire logging, on forb and pollinator communities and on forb reproduction. My research addresses these gaps in knowledge and asks: 1) how do floral and bee communities respond to post-wildfire logging and how do their responses differ between two different-aged fires, and 2) how does post-wildfire logging influence forb reproduction and pollen limitation of reproduction in an older wildfire? In the more recent fire, floral and bee density and species richness were higher in logged than unlogged areas. By contrast, in the older fire, forb and bee communities were similar between logged and unlogged areas. Unexpectedly, we found large inter- and intra-annual variation in the effects of post-wildfire logging. Lastly, in the older fire, there were no effects of post-wildfire logging on forb reproduction, but plants were pollen limited in unlogged areas. This suggests that plants in unlogged areas are able to augment their reproductive output with supplemental pollen resources, but plants in logged areas cannot. Together, these results suggest that post-wildfire logging is beneficial for forbs and pollinators in the short-term, and these positive effects depend on time of growing season and sampling year. However, post-wildfire logging may be detrimental for forb reproduction in the long-term.
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. Mangold
Centaurea 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.
Interaction turnover among pollination networks across space, time, and environment
(Montana State University - Bozeman, College of Letters & Science, 2013) Simanonok, Michael Peter; Chairperson, Graduate Committee: Laura Burkle
Pollination networks provide an ideal system in which to test hypotheses around interaction turnover across ecologically meaningful gradients, as there is already baseline understanding of plant and pollinator communities. Parallel declines in plants and pollinators imply that disruption of interactions between species in pollination networks may be leading to pollinator declines; therefore, beginning to understand how plant-pollinator interactions turnover through space, time, and environment could be vital for future conservation and management efforts. I investigated i.) how do plant and pollinator species diversity (i.e., richness and evenness), phenology, and composition change across space, time, and environment, ii.) how do interactions between pollination networks turn over across these same gradients (i.e., space, time, and environment), and iii.) what is the relative contribution of species turnover (plant, pollinator, or both simultaneously) vs. host switching to interaction turnover among pollination networks? Field work was conducted during summer 2012 on the Beartooth Plateau, an alpine ecosystem in Montana and Wyoming, with weekly observations of plant-pollinator interactions and the floral community across the growing season. Community diversity and composition were compared across space, time, elevation, slope, and aspect using linear regressions, t-tests, and principle coordinate analysis. Interaction turnover was calculated between all possible pair wise combinations of study site and week and compared across, space, time, elevation, slope, and aspect using a partial Mantel test and linear regressions. We found that interaction turnover mostly occurred due to simultaneous species turnover of both plant and pollinator communities with host-switching having marginal contribution. Furthermore, interaction turnover occurred across temporal and environmental gradients, with no significant variation across spatial scales. These results differ greatly from inter-annual patterns on the contribution of species turnover vs. host switching, however some results may be due to sampling or scale limitations. It is possible that host switching does not readily occur within-season, but more work is needed for confirmation. Spatial and environmental patterns remain possible, but did not emerge at the extents used herein. This study represents the first instance of the partitioning of interaction turnover into individual species components for a pollination network, and the first to do so intra-annually.
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.

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