- Author: Kathy Keatley Garvey
In a newly published article titled, “Flower Plantings Support Wild Bee Reproduction and May Also Mitigate Pesticide Exposure Effects,” in the Journal of Applied Ecology, the eight-member team related that "to address the potential of flower plantings to mitigate bee pesticide exposure and effects and support bee reproduction, we established replicated sites where half contained flower plantings. We used sentinel bees to assess nesting and reproduction, quantified local and landscape flower availability, and used bee-collected pollen to quantify bee pesticide exposure and forage resource use. We asked the following questions:
- To what extent do bees use flower plantings?
- Do flower plantings promote bee reproduction?
- Do flower plantings modify bee pesticide exposure and effects on reproduction?"
The paper is the work of co-lead authors Maj Rundlöf and Clara Stuligross, and co-authors Arvid Lindh, Rosemary Malfi, Katherine Burns, John Mola, Staci Cibotti and Professor Williams.
- Sustainable agriculture relies on pollinators, and wild bees benefit yield of multiple crops. However, the combined exposure to pesticides and loss of flower resources, driven by agricultural intensification, contribute to declining diversity and abundance of many bee taxa. Flower plantings along the margins of agricultural fields offer diverse food resources not directly treated with pesticides.
- To investigate the potential of flower plantings to mitigate bee pesticide exposure effects and support bee reproduction, we selected replicated sites in intensively farmed landscapes where half contained flower plantings. We assessed solitary bee Osmia lignaria and bumble bee Bombus vosnesenskii nesting and reproduction throughout the season in these landscapes. We also quantified local and landscape flower resources and used bee-collected pollen to determine forage resource use and pesticide exposure and risk.
- Flower plantings, and their local flower resources, increased O. lignaria nesting probability. Bombus vosnesenskii reproduction was more strongly related to landscape than local flower resources.
- Bees at sites with and without flower plantings experienced similar pesticide risk, and the local flowers, alongside flowers in the landscape, were sources of pesticide exposure particularly for O. lignaria. However, local flower resources mitigated negative pesticide effects on B. vosnesenskii reproduction.
- Synthesis and applications. Bees in agricultural landscapes are threatened by pesticide exposure and loss of flower resources through agricultural intensification. Therefore, finding solutions to mitigate negative effects of pesticide use and flower deficiency is urgent. Our findings point towards flower plantings as a potential solution to support bee populations by mitigating pesticide exposure effects and providing key forage. Further investigation of the balance between forage benefits and added pesticide risk is needed to reveal contexts where net benefits occur.
Journal of Applied Ecology, a publication of the British Ecological Society, publishes novel, high-impact papers on the interface between ecological science and the management of biological resources.
- Author: Kathy Keatley Garvey
Yes, according to UC Davis community ecologist and doctoral candidate Danielle Rutkowski and her colleagues in their newly published research in the Royal Entomological Society's Journal of Ecological Entomology.
The research, “Bee-Associated Fungi Mediate Effects of Fungicides on Bumble Bees,” provides direct evidence that fungi can benefit both survival and reproduction in two species of bumble bees, Bombus vosnesenskii, and B. impatiens. The research also suggests that yeast, commonly found in the gut of bumble bees, may be more important than originally thought.
“Bumble bees are important pollinators that face threats from multiple sources, including agrochemical application,” said Rutkowsi, the lead researcher-author. “Declining bumble bee populations have been linked to fungicide application, which could directly affect the fungi often found in the stored food and gastrointestinal (GI) tract of healthy bumble bees.”
“I tested if fungicides commonly applied in orchard systems affected yeasts and the health of their bee hosts, and if feeding those bees their fungi after fungicide exposure could rescue them,” said Rutkowski, who studies with major professors Rachel Vannette and Richard Karban, community ecologists in the Department of Entomology and Nematology.
“Bombus vosnesenskii (commonly known as the yellow-faced bumble bee), is native to California and we reared colonies of it from wild-caught queens,” Rutkowski said. “In this species, we observed strong negative effects of fungicide and the ability of bee-associated fungi to rescue bees from these negative effects. The other species, Bombus impatiens, is native to the eastern United States, but is commonly produced and sold commercially for pollination. In this species, we did not find any negative impacts of fungicide, but the addition of yeasts was very beneficial for bee survival and offspring production.”
“Although most previous work on bee microbiomes has focused on bacteria and their role in bee health, Danielle's work suggests that yeasts --which are commonly found in association with bumble bees--may be more important than previously thought,” Vannette said. “This has been hinted at in the literature but rarely tested directly.”
Rutkowski examined the interactive effects of the fungicide propiconazole and fungal supplementation on the survival, reproduction and microbiome composition of microcolonies (queenless colonies) using the two species.
Both B. vosnesenskii and B. impatiens benefitted from fungal addition but in different ways. fungicide exposure decreased survival in B. vosnesenskii, while fungal supplementation mitigated fungicide effects. For B. impatiens, fungicide application had no effect, but fungal supplementation improved survival and offspring production.
“Because the effect of fungicides on yeasts and bees takes a few weeks to observe, it is not detected in short term LD50 trials,” Vannette said, “and therefore could be an unrecognized threat to bumble bees and their symbionts.”
Other co-authors of the paper are entomologist Eliza Litsey and environmental scientist Isabelle Maalouf.
More research is planned to determine the mechanism by which yeasts can affect bee health, and which fungicides affect bee-associated yeasts.
“I'm currently working on a project to determine the mechanisms behind the positive effects of yeast addition that we observed,” Rutkowski said. “In some bees and other insects, fungi can produce nutritionally important compounds for their host, and I'm currently trying to determine if this is the case for bumble bees as well.”
“Additionally, I'm planning on following up some of the interesting results on differences between bumble bee species by determining how associated microbial communities differ between wild and commercially-reared bumble bees,” Rutkowski said. “In this current paper, we found that the fungal communities associated with the commercially-sourced bees were less diverse and less abundant, and I'm hoping to determine if that's a common pattern.”
Rutkowski, who joined the UC Davis doctoral program in 2018, won the President's Prize (first-place) in her category for her graduate student research presentations at the 2017 and 2021 Entomological Society of America meetings. A 2018 graduate of Cornell University, summa cum laude, she holds a bachelor of science degree in entomology and biological sciences, with a concentration in ecology and evolution.
Rutkowski's research drew support from her three-year USDA National Institute of Food and Agriculture grant.