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 email@example.com 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.
Graduate student Katharina Ullmann of the Neal Williams lab is the host.
“Many recent studies have shown that enhancing floral resources in intensive agricultural landscapes promotes species richness of flower-visitor communities, but to date, it is not known whether such effects are transient, merely concentrating individuals from across the larger landscape at flower-rich patches,” M'Gonigle says in his abstract. “Long-term data series and use of occupancy models are particularly helpful in determining whether these richness patterns actually reflect true increases in occupancy, or not. Further, such models can also determine whether enhanced occupancy results from decreased extinction rates, increased colonization rates, or both, providing information that is useful for conservation planning. “
“To date, these models have not been applied to the study of pollinators and their response to restoration. Here we present the results from a long-term study chronicling how restoration and subsequent maturation of native plant hedgerows affects occupancy, persistence and colonization of bees and syrphid flies in the Central Valley of California. Using a hierarchical occupancy model, we show that restoration via the introduction of perennial flowering native shrubs promotes the between-season persistence, but not colonization, of both bees and syrphid flies. This increased occupancy has the long-term effect of leading to the assembly of more diverse communities. We also find that, for native bees, hedgerow restoration has a greater impact on floral resource specialists than generalists."
M'Gonigle received his bachelor of science degree in mathematics (honors with distinction) from the University of Victoria in 2005; his master's degree in zoology from the University of British Columbia in 2006, and his doctorate in zoology from the University of British Columbia in 2011.
The recipient of numerous awards, he won the Dan David Prize ($15,000 prize for doctoral work) in 2011 and was named the top teaching assistant in his department (based on student course evaluations encompassing 70 teaching assistants) in both 2008 and 2011. Considered an outstanding speaker, he won “best talk” awards from several scientific organizations.
His most recent publications include:
Frishkoff, L.O., Karp, D.S., M'Gonigle, L.K., Mendenhall, C.D., Zook, J., Kremen, C., Hadley, E.A., and Daily, G.C. Land Use Transforms the Tree of Life. In prep.
M'Gonigle, L.K., Ponisio, L.C., and Kremen, C. Habitat restoration promotes pollinator persistence in intensively managed agriculture. In prep.
Ball-Damerow, J.E., M'Gonigle, L.K., Resh, V.H. Landscape, climate, and habitat factors influencing assemblages of dragonflies and damselflies (Odonata) in California and Nevada. Submitted.
Ball-Damerow, J.E., M'Gonigle, L.K., Resh, V.H. Changes in occurrence, richness, and biological traits of dragonflies and damselflies (Odonata) in California and Nevada over the past century. Submitted.
M'Gonigle's seminar is scheduled to be video-recorded for later posting on UCTV.
(Editor's Note: See remainder of Spring Quarter Seminars, UC Davis Department of Entomology and Nematology)
The seminar, part of the UC Davis Department of Entomology and Nematology's spring quarter seminars, will be hosted by associate professor/pollination ecologist Neal Williams.
"The supply of managed honeybees for crop pollination service is both increasingly uncertain and being outpaced by a growing demand," Lonsdorf says in his abstract. "It is increasingly recognized that farmers should respond by integrating native pollinator-friendly habitat into standard farming practices. Furthermore, recent findings indicate that both farm and landscape-level factors affect the supply of pollinators."
"This begs the question, how much pollinator-friendly is needed in the landscape to maximize yields? Here, I apply a quantitative model of pollination service to answer this question as a function of a crop's dependence on native pollination. Not surprisingly, as the dependence on pollination increases, the optimal amount of pollinator-friendly habitat in the landscape increases. Moreover, as the quality of on-farm habitat for pollinators increases, the optimal amount of crop in the landscape increases. We uncover a pollination service version of the “tragedy of the commons” in which an individual may increase their profits by converting pollinator-providing habitat to crop while the entire landscape's value declines."
Said Williams: "Eric is an expert in spatial modeling of ecosystems services including pollination and also in decision analysis. Eric's landscape models of pollinators and pollination services form the basis of several recent global reviews of pollination response to anthropogenic disturbance and environmental change."
Lonsdorf received his doctorate in ecology, evolution and behavior in 2004 from the University of Minnesota, Twin Cities campus, and his bachelor's degree in 1996 in biology (magna cum laude) from Carleton College, Northfield, Minn.
Prior to joining Franklin and Marshall, he worked for the Chicago Botanic Garden and directed the Lincoln Park Zoo's Urban Wildlife Institute in Chicago. He currently develops ecological models for decision-makers faced with challenging problems in conservation biology and natural resource management.
Lonsdorf's seminar is scheduled to be video-recorded for later posting on UCTV.
Ullmann, based in the UC Davis Department of Entomology and Nematology, will provide an overview of native bee diversity in Yolo County, discuss threats to native bees in the region, and explore efforts to enhance habitat for pollinators.
Ullmann also will highlight the importance of native bees for agricultural production, and the efforts of local organizations, landowners and researchers to identify and enhance plant communities that support pollinator populations in the context of global change. She will provide a slide show of pollinators, including honey bees, bumble bees, butterflies, and syrphid flies.
In the Williams lab, Ullmann focuses her research on pollinator habitat restoration and understanding how pollinator species are able to persist in highly modified landscapes, including agricultural lands. Williams, a pollination ecologist, is an associate professor.
Her talk will be CreekSpeak’s fifth of 2013 in its six-month series of community talks about the nature, culture and history of the region. A $5 donation is requested from those who have not yet joined the council.
The final CreekSpeak talk of 2013 will be on Oct. 17 when Marilyn Ramenofsky will speak on “Birds of Putah Creek.”
Putah Creek Council is dedicated to the protection and enhancement of Putah Creek and its tributaries through advocacy, education and community-based stewardship. They envision Putah Creek as "a thriving corridor of native riparian and aquatic ecosystems connecting the Coast Ranges to the Sacramento River and the Delta." They seek a watershed community of people who value their creek and are committed to its stewardship, according to their website.