Two scientists—lead author Charlie Nicholson, a UC Davis postdoctoral scholar formerly with the University of Vermont (UVM), and senior author Paul Egan, a senior researcher at the Swedish University of Agricultural Sciences--analyzed 117 published research papers on natural hazards that threaten pollinators and pollination.
Their paper, “Natural Hazard Threats to Pollinators and Pollination,” published in the journal Global Change Biology, sounds the alarm to scientists and policy makers to place the impacts of natural hazards at the center of future research in order to emphasize conservation and reduce disaster risks.
Previous research on threats to pollinators primarily focuses on direct human impacts, but scientific knowledge of natural hazard impacts has not been synthesized yet, they said.
“The frequency and intensity of many natural hazards, such as floods and storms, are set to increase under climate change, so bringing together the evidence of these impacts is really timely,” said Nicholson, who joined the Neal Williams lab, UC Davis Department of Entomology and Nematology, earlier this year.
“Research was not evenly distributed across pollinator groups, with many impacts recorded for bees, Lepidoptera, flies. wasps, birds, beetles, and bats,” they wrote. “Studies tended to report impacts to pollinators in terms of abundance (41 percent of responses), species richness (19 percent), and various population-level effects (19 percent), whereas impacts to plants were measured in terms of reproductive success (39 percent), floral traits (27 percent), and species richness (11 percent).”
Scrutinizing the scientific literature involved “poring over many accounts of the powerful destructive force of nature, but also searching for some pretty unexpected hazards such as solar flares, or the Earth's electromagnetic effect on pollinators,” Nicholson said.
The work also highlights disparities in the burden of evidence. Said Egan: “We see that this type of pollination research is strongly biased toward economically developed regions, whereas it is smallholder farmers and developing countries that will bear the largest impacts. Their existing vulnerabilities and dependence on crop pollinators tend to be higher.”
Nicholson and Egan identified several future research priorities, including the need to understand impacts to yields through impacted pollination services and to better characterize and contextualise the nature of exposure to natural hazards.
“Taken together, our findings show that the response of pollinators and pollination to natural hazards depends on the type of disturbance and level of biological organization observed and that different pollinator taxa can respond very differently to the same hazard,” they wrote.
Formas, a Swedish government research council for sustainable development, funded the research.
Nicholson holds a doctorate in natural resources (2018) from UVM. Egan received his doctorate in plant animal interactions from Trinity College Dublin in Ireland in 2015.
The two-year research, led by Ola Lundin, a former postdoctoral fellow in the Neal Williams lab, UC Davis Department of Entomology and Nematology and published in the Journal of Applied Ecology, details what plants proved most attractive to honey bees, wild bees and other pollinators, as well as what drew such natural enemies as predators and parasitic wasps.
The research, “Identifying Native Plants for Coordinated Habitat Management of Arthropod Pollinators, Herbivores and Natural Enemies,” is co-authored by Williams, professor of entomology and a Chancellor's Fellow at UC Davis; and project specialist Kimiora Ward of the Williams lab.
“I hope this study can inform selection of plants that support pollinators and natural enemies without enhancing potential pests,” said Lundin, first-author of the paper and now a postdoctoral fellow in the Department of Ecology, Swedish University of Agricultural Sciences, Uppsala.
“Planting wildflowers is a key strategy promoted nationally to support wild and managed bees,” said Williams. “Successful adoption of these plantings in agricultural landscapes will require that they not only support pollinators but that they also avoid supporting too many pests. Plant selection going forward will need to balance multiple goals of pollinators pest management and other functions. This research is a first step on the path to identifying plants that will meet these goals."
The three scientists, who conceived the ideas and developed the methodology for the research project, established 43 plant species in a garden experiment on the grounds of the Harry H. Laidlaw Jr. Honey Bee Research Facility at UC Davis. They selected plant species that were drought-tolerant; native to California (except for buckwheat, Fagopyrum esculentum, known to attract natural enemies and widely used in conservation biological control); and, as a group, covered a range of flowering periods throughout the season.
“For early season bloom, Great Valley phacelia (Phacelia ciliata) was a real winner in terms of being attractive for both wild bees and honey bees,” Lundin said. “Elegant Clarkia (Clarkia unguiculata) flowers in late spring and was the clearly most attractive plant for honey bees across the dataset. The related Fort Miller Clarkia (C. williamsonii) was also quite attractive for honey bees and had the added benefit that a lot of minute pirate bugs visited the flowers.”
Lundin said that common yarrow (Achillea millefolium) “attracted “attracted the highest numbers of parasitic wasps but also many herbivores, including Lygus bugs.”
“In general a lot of parasitic wasps were found on Asteraceae species (the daisy family) and this was a somewhat surprising result considering that they have narrow corollas, and for parasitic wasps relatively deep corollas that can restrict their direct access to nectar. Under the very dry conditions in late summer, Great Valley gumplant (Grindelia camporum) and Vinegarweed (Trichostema lanceolatum) both performed well and attracted high numbers of wild bees.”
The team found that across plant species, herbivore, predator and parasitic wasp abundances were “positively correlated,” and “honey bee abundance correlated negatively to herbivore abundance.”
The take-home message is that “if you're a gardener or other type of land manager, what you'd likely prefer would be a mix of some of the most promising plant species taking into account their individual attractiveness for these arthropod groups, plus several more factors including costs for seed when planting larger areas,” Lundin said.
“Plant choice can also depend on how you weigh the importance of each arthropod group and whether you are interested in spring, summer or season-long bloom,” Lundin added. Those are some of the questions that the Williams lab plans to explore in future projects.
Williams praised the “uniquely capable team that came together.”
“Ola is an emerging leader in considering integrated management of pests and pollinators and Kimiora is a known expert in developing regionally-relevant plant materials to support pollinators,” Williams said. “They and some talented UC Davis undergraduates--notably Katherine Borchardt and Anna Britzman--compiled a tremendously useful study.”
The overall aim of the study “was to identify California native plants, and more generally plant traits, suitable for coordinated habitat management of arthropod pollinators, herbivores and natural enemies and promote integrated ecosystem services in agricultural landscapes,” the researchers wrote.
More specifically, they asked:
- Which native plants among our candidate set attract the highest abundances of wild bees, honeybees, herbivores, predators, and parasitic wasps,
- If the total abundances of arthropods within these functional groups across plant speacies are related to the peak flowering week, floral area, or flower type of the focal plant species, and
- If the total abundances of arthropods within these functional groups are correlated to each other across plant species.
“A first critical step for design and implementation of multifunctional plantings that promote beneficial arthropods while controlling insect pests is to identify suitable plant species to use,” the authors wrote in their abstract. “We aimed to identify California native plants and, more generally, plant traits suitable for the coordinated management of pollinators (wild bees and honey bees), insect herbivores and arthropod natural enemies (predators and parasitic wasps).”
At the time, the Laidlaw grounds included nearly 50 bee colonies: some 20 to 40 honey bee colonies, and eight managed research colonies of the yellow-faced bumble bee, Bombus vosnesenkii.
The project received funding from the USDA Resources Conservation Service, USDA Agricultural Marketing Service, USDA National Institute of Food and Agriculture and a Swedish foundation for scientific research, the Carl Tryggers Stiftelse for Vetenskaplig Forskning.
Nectar-living microbes release scents or volatile compounds, too, and can influence a pollinator's foraging preference, according to newly published research led by UC Davis community ecologist Rachel Vannette.
The groundbreaking research, published in the current edition of New Phytologist journal, shows that nectar-inhabiting species of bacteria and fungi “can influence pollinator preference through differential volatile production,” said Vannette, an assistant professor in the UC Davis Department of Entomology and Nematology.
“This extends our understanding of how microbial species can differentially influence plant phenotype and species interactions through a previously overlooked mechanism,” Vannette said. “It's a novel mechanism by which the presence and species composition of the microbiome can influence pollination.”
“Broadly, our results imply that the microbiome can contribute to plant volatile phenotype,” she said. “This has implications for many plant-insect interactions.”
Their paper, titled “Nectar-inhabiting Microorganisms Influence Nectar Volatile Composition and Attractiveness to a Generalist Pollinator,” may explain in part the previous documented extreme variation floral volatiles that Robert Junker of University of Salzburg, Austria, and his team found; New Phytologist published their work in March 2017.
Although microbes commonly inhabit floral nectar, microbial species differ in volatile profiles, they found. “Honey bees detected most of the microbial volatiles or scents that we tested,” Vannette said, “and they distinguished the solutions of yeasts or bacteria based on volatiles only.” This suggests that pollinators could choose among flowers based on the microbes that inhabit those flowers.
The yeast Metschnikowia reukaufii produced the most distinctive compounds (some shared with the fruity flavors in wine) and was the most attractive of all microbes compared. This yeast is commonly found in flower nectar and is thought to hitch a ride on pollinators to travel from one flower to the next. Its scent production may help it attract pollinators, which then help the yeast disperse among flowers.
The Harry H. Laidlaw Jr. Honey Bee Research Facility, UC Davis, provided the honey bees. More than 20 species of flowers--mostly natives--were used in the survey, including canyon delphinium or canyon larkspur (Delphinium nudicaule), sticky monkey flower (Mimulus aurantiacus), salvia (Lepechinia calycina) and purple Chinese houses (Collinsia heterophylla). The samplings were done in the spring and early summer, when the natives are at their peak.
Co-authors of the paper are Caitlin Rering, postdoctoral fellow at USDA-ARS, Gainesville, Fla.; John Beck researcher at USDA-ARS; Griffin Hall, junior specialist in the Vannette lab; and Mitch McCartney in UC Davis Department of Mechanical and Aerospace Engineering.
The USDA and USDA-ARS funded the research.
In newly published research in the journal Ecology, Vannette noted that floral nectar is produced by many plants to reward pollinators, but this sugary secretion often contains chemical compounds that are bitter tasting or toxic, and can deter pollinators. Plants including citrus (Citrus), tobacco (Nicotiana), milkweed (Asclepias), turtlehead (Chelone), Catalpa, and others produce nectar containing bioactive compounds, including deterrent or toxic compounds.
“This poses a paradox of toxic nectar: why are deterrent or harmful compounds present in a resource intended to attract pollinators?” she asked. “One hypothesis is that these compounds reduce microbial growth, which could otherwise spoil the nectar resource.”
Vannette, an assistant professor in the UC Davis Department of Entomology and Nematology, and her colleague Tadashi Fukami, associate professor at Stanford University, tested this hypothesis by growing yeasts and bacteria in sugar solutions spiked with a chemical compounds that are found in nectar.
“We examined effects on the growth of microbes isolated from nectar and non-nectar sources. Contrary to expectations, chemical compounds only weakly inhibited microbial growth in most cases. Interestingly, some microorganisms even grew better in the presence of plant compounds, like nicotine. But most surprising, we found that microbial growth in nectar reduced nectar toxicity, decreasing the concentration of chemical compounds in some nectar solutions.”
Microbial effects on nectar, in turn, increased consumption of nectar containing chemical compounds by honey bee pollinators, she said. “We found that microorganisms in nectar can both reduce the concentration of some plant compounds in nectar and increase consumption of nectar that does contain these compounds. This indicates that although ‘toxic nectar' does not strongly inhibit microbial growth in nectar, microbes modify the palatability of nectar to pollinators, which can change foraging behaviors and may reduce selection on this trait in nectar.”
The paper, exploring the effects of nectar-inhabiting microbes on chemical compounds found in nectar and nectar consumption by pollinators, “demonstrates that the compounds in nectar—such as on citrus blossoms--do not inhibit microbial growth, Vannette said. “However, yeasts and bacteria that grow in nectar can modify the effects of plant chemical compounds on pollinator foraging and nectar consumption..”
In her abstract, Vannette wrote “Secondary metabolites that are present in floral nectar have been hypothesized to enhance specificity in plant-pollinator mutualism by reducing larceny by non-pollinators, including microorganisms that colonize nectar. However, few studies have tested this hypothesis. Using synthetic nectar, we conducted laboratory and field experiments to examine the effects of five chemical compounds found in nectar on the growth and metabolism of nectar-colonizing yeasts and bacteria, and the interactive effects of these compounds and nectar microbes on the consumption of nectar by pollinators.”
“In most cases, focal compounds inhibited microbial growth, but the extent of these effects depended on compound identity, concentration, and microbial species. Moreover, most compounds did not substantially decrease sugar metabolism by microbes, and microbes reduced the concentration of some compounds in nectar. Using artificial flowers in the field, we also found that the common nectar yeast Metschnikowia reukaufii altered nectar consumption by small floral visitors, but only in nectar containing catalpol. This effect was likely mediated by a mechanism independent of catalpol metabolism. Despite strong compound-specific effects on microbial growth, our results suggest that the secondary metabolites tested here are unlikely to be an effective general defense mechanism for preserving nectar sugars for pollinators. Instead, our results indicate that microbial colonization of nectar could reduce the concentration of secondary compounds in nectar and, in some cases, reduce deterrence to pollinators.”
The research, “Nectar Microbes Can Reduce Secondary Metabolites in Nectar and Alter Effects on Nectar Consumption by Pollinators,” appears on the Ecology website, http://onlinelibrary.wiley.com/doi/10.1890/15-0858.1/full
The research was funded by the Gordon and Betty Moore Foundation, the National Science Foundation, and Stanford University.
Future work will examine how microbial modification of nectar traits influences floral attractiveness, how microbial growth may modify the specificity of plant-pollinator interactions, and if microbial effects vary among plant species.
Vannette, a former postdoctoral fellow at Stanford University, joined the UC Davis Department of Entomology and Nematology in September 2015. “I am interested in understanding and predicting how microbial communities influence interactions between plants and insects,” she said. “In the Vannette lab (in Briggs Hall), we use tools and concepts from microbial ecology, chemical ecology, and community ecology to better understand the ecology and evolution of interactions among plants, microbes and insects."
Ecology journal research paper
That's the topic of a special conference--open to the public –set from 10 a.m. to 4 p.m., Wednesday, Sept. 9 at the UC Davis Conference Center, 550 Alumni Lane. UC Davis researchers and state officials will address the crowd, announced conference coordinator Dave Fujino, director of the UC Davis-based California Center for Urban Horticulture.
“We are pleased to have such a knowledgeable lineup of UC Davis researchers who will clarify the issue of impact of neonicotinoid impacts on pollinators by summarizing and presenting the past and current science-based research,” Fujino said. “We are also fortunate to have additional presentations on the regulation guidelines on neonicotinoids and their role in controlling invasive pests in California, and a diverse group of stakeholders participating in a panel discussion on the neonicotinoid issue.”
Neonicotinoids, recently implicated in the worldwide die-off of pollinators, including honey bees, are a class of neuro-active insecticides chemically similar to nicotine. Considered important in the control of many significant agricultural and veterinary pests, they target the central nervous system of insects, resulting in paralysis and death. “Neonics,” as they're called, are commonly used on farms, and around homes, schools, and city landscapes.
Michael Parrella, professor and chair of the UC Davis Department of Entomology, will provide an overview of the current use of neonicotinoids and the role of honey bees in California agriculture. Six other speakers are scheduled, along with a panel discussion.
The speakers include:
- Brian Leahy, director of the California Department of Pesticide Regulation, who will discuss “California Pesticide Regulation of Neonicotinoids”
- Nick Condos, director of the Plant Health and Pest Prevention Services Division, California Department of Food and Agriculture, “Neonicotinoid Risks Associated with Invasive Species Management”
- Karen Jetter, associate project economist, UC Agricultural Issues Center, “Trends in Neonicotinoid Usage in California Agriculture and the Control of Invasive Species”
- Margaret “Rei” Scampavia, a doctoral candidate who studies with major professors Neal Williams and Ed Lewis of the UC Davis Department of Entomology and Nematology, “Past Neonicotinoid and Bee Research”
- Elina Lastro Niño, Extension apiculturist based at the Harry H. Laidlaw Honey Bee Research Facility, UC Davis, “Current Neonicotinoid and Bee Research.”
The California Center for Urban Horticulture (CCUH) will co-host the event with the UC Davis Department of Entomology and Nematology and the UC Agriculture and Natural Resources.
Sponsors include California Association of Nurseries and Garden Centers (CANGC), a trade organization founded in 1911 to promote and protect the California nursery industry; Four Winds Growers, based in Winters, Calif.; Scotts Miracle-Gro, a company headquartered in Marysville, Ohio, and known as the world's largest marketer of branded consumer lawn and garden products; and Monrovia, a horticultural craftsmen company headquartered in Azusa, Calif.
At the close of the conference, Fujino will preside over a panel discussion on neonicotinoid issues and concerns. Questions and answers from the audience will follow. The panel is to include a UC Cooperative Extension farm advisor, and representatives from the California Association of Nurseries and Garden Centers, Home Depot, Scotts Miracle-Gro, Bayer CropScience and the American Beekeeping Federation.
The registration fee of $50 will include lunch, as well as the post-conference social hour. To register, access the CCHU website at http://ccuh.ucdavis.edu/public/copy_of_public/neonicotinoid-pollinator-conference-2015/neonic or contact CCUH representative Kate Lincoln at firstname.lastname@example.org or (530) 752-6642.
The European Union recently adopted a proposal to restrict the use of three pesticides belonging to the neonicotinoid family (clothianidin, imidacloprid and thiametoxam) for a period of two years. In addition, the U.S. Fish and Wildlife Service announced that by January 2016, it will ban the use of seeds treated with neonicotinoid pesticides and the use of crops improved through biotechnology throughout the 150 million acres managed by the National Wildlife Refuge System.