- Author: Kathy Keatley Garvey
Stuligross, who received her doctorate in ecology on Sept. 9 from UC Davis, will present her exit seminar, "Individual and Combined Effects of Resource and Pesticide Stressors on Wild Bees and a Potential Strategy to Mitigate Impacts" at 10 a.m., Tuesday, Oct. 18 in Room 1022 of Green Hall.
The seminar, open to all interested persons, also will be virtual. The Zoom link is https://ucdavis.zoom.us/j/3661107142.
Stuligross researches nutrition and pesticide exposure and their comparative effects on the blue orchard bee, Osmia lignaria, and the yellow-faced bumble bee, Bombus vosnesenskii. Pollination ecologist Neal Williams, professor in the Department of Entomology and Nematology, served as her major professor.
"I am doing a short postdoc with Neal Williams this fall, and in January I will start a postdoctoral research position with Nicole Rafferty at UC Riverside," Stuligross said.
"Anthropogenic environmental changes present multiple stressors that together impact biodiversity and ecosystem function," Stuligross writes in her abstract. "Among these, pesticide exposure and the loss of flowering plants are ubiquitous across contemporary landscapes and threaten the persistence of bee populations. In this dissertation, I explored the individual and combined effects of pesticide and floral resource stressors on bee behavior, reproduction, and population persistence, as well as a potential strategy for mitigating these impacts. I used a combination of manipulative field cage experiments and landscape studies to examine these stressors and their impacts at different scales.
"Because bees often experience pesticide and resource stressors simultaneously, I first examined the potential for interactive effects of these stressors, as well as their individual impacts on wild bees. I established a fully crossed design in field cages; nesting female Osmia lignaria, the solitary blue orchard bee, accessed wildflowers at high or low densities, treated with or without the common insecticide, imidacloprid. In Chapter 1, I showed that pesticide exposure and floral resource scarcity combined additively to dramatically alter multiple vital rates, including reduced reproduction and a male-biased offspring sex ratio. In Chapter 2, I quantified behavioral responses in the same experiment, revealing that the resource and pesticide stressors had differential impacts with consequences for bee populations and potentially for pollination services through individual behavioral changes. Limited floral resources required bees to make fewer, longer foraging trips as well as misidentify their nests more often upon return from these trips. Bees exposed to pesticides made shorter foraging trips and did not compensate for this by taking more trips, reducing their overall foraging activity. Pesticide exposure also interacted with age to affect antagonistic behavior."
"In Chapter 3, I examined the carryover effects of past pesticide exposure on wild bees. Using the offspring from the previous cage experiment with known pesticide exposure backgrounds, I re-established the field cages and released bees in a crossed design with pesticide exposure or no exposure in each year. Thus, some bees experienced pesticides over two generations and others not at all. Regardless of the past exposure history, pesticides in the second year reduced reproduction. For bees that were also exposed in the past, the exposure over two years additively impaired individual performance, leading to a nearly fourfold estimated reduction in bee population growth. Furthermore, even past exposure by itself, regardless of exposure in the second year, led to a decline in offspring production."
"In Chapter 4, I collaborated with Maj Rundlöf to investigate the potential for wildflower plantings to mitigate the negative effects of pesticide exposure in agricultural landscapes. We assessed the nesting and reproduction of O. lignaria and the bumble bee Bombus vosnesenskii in replicate agricultural landscapes, half of which contained a wildflower planting next to the nest or colony. We collected pollen from foraging bees to determine resource use and pesticide residues. The wildflower plantings were a source of pesticide exposure, especially for O. lignaria, but also supported O. lignaria nesting. The landscape-level floral resources better predicted B. vosnesenskii colony success, but the local flower resources mitigated the negative effects of pesticides on their reproduction."
"These chapters together show that two common environmental stressors combine to negativel impact bees. They also reveal potential mechanisms underlying impacts of the stressors on reproduction and population growth. My dissertation highlights the importance of mitigating the negative effects of pesticides and floral resource limitation, especially in agricultural landscapes where the two stressors often co-occur. Finally, this work offers insight into how the stressors could be mitigated through an emerging strategy to diversity agricultural landscapes."
Stuligross received her bachelor of arts degree in environmental studies in 2014 in Indiana from Earlham College, Richmond, where she minored in biology and outdoor education. At UC Davis, she was awarded a 2017-22 National Science Foundation Graduate Research Fellowship, and a 2016-18 UC Davis Graduate Group in Ecology Fellowship.
Recognized nationally for her research, Stuligross scored second place in the Entomological Society of America's 2020 President's Prize competition. Her research posters also won the top award at the UC Davis Graduate Student Symposium in Ecology in both 2019 and 2021.
Stuligross and her colleague, Maj Rundlöf, are the co-first authors of "Flower Plantings Support Wild Bee Reproduction and May Also Mitigate Pesticide Exposure Effects," published in May 2022 in the Journal of Applied Ecology. She was the lead author of "Past Insecticide Exposure Reduces Bee Reproduction and Population Growth Rate," published in November 2021 in the Proceedings of the National Academy of Sciences, and also the lead author of "Pesticide and Resource Stressors Sdditively Impair Wild Bee Reproduction," published in September 2020 in The Proceedings of the Royal Society B.
Stuligross has also co-authored a number of other research publications, most recently:
- "A Meta-Analysis of Single Visit Pollination Effectiveness Comparing Honeybees and Other Floral Visitors," American Journal of Botany
- "Impact of 'Nonlethal' Tarsal Clipping on Bumble Bees (Bombus vosnesenskii) May Depend on Queen Stage and Worker Size," Journal of Insect Conservation
Want to learn more about wild bees, also known as undomesticated bees? Be sure to read the UC-authored book, California Bees and Blooms: A Guide for Gardeners and Naturalists. It's the work of Gordon Frankie of UC Berkeley, the late Robbin Thorp of the UC Davis Department of Entomology and Nematology; Barbara Ertter of UC Berkeley; and photographer Rollin Coville, alumnus of UC Berkeley. California is home to more than 1600 species of undomesticated or wild bees.
- Author: Kathy Keatley Garvey
"Imidacloprid disrupts the nerve's ability to send a normal signal, and the nervous system stops working the way it should," says the National Pesticide Information Center (NPIC).
Used in products sold in the United States since 1994, "Imidacloprid is much more toxic to insects and other invertebrates than it is to mammals and birds because it binds better to the receptors of insect nerve cells," according the NPIC's Fact Sheet.
Now a newly published, two-year UC Davis study reveals that normal exposure to imidacloprid generates a multi-generational effect on the blue orchard bee, Osmia lignaria, reducing both reproduction and population growth.
The research, "Past Insecticide Exposure Reduces Bee Reproduction and Population Growth," by doctoral ecology candidate Clara Stuligross and her co-author, major professor Neal Williams of the UC Davis Department of Entomology and Nematology, is published in the current edition of the Proceedings of the National Academy of Sciences.
The blue orchard bee, sometimes nicknamed BOB, is a native bee active in the early spring. Metallic blue in color and smaller than a honey bee, it is a solitary mason bee often managed commercially to pollinate almond orchards. The bees are also considered excellent pollinators of apple, pear and cherry trees and efficient pollinators of blueberries.
“We reveal that pesticide exposure, both directly to foraging bees and via carryover effects from past exposure, dramatically reduced bee reproduction, which reduced population growth,” they wrote. “Carryover effects reduced bee reproduction by 20% beyond current impacts on foraging bees, exacerbating the negative impact on population growth rates. This indicates that bees may require multiple generations to recover from a single pesticide exposure; thus, carryover effects must be considered in risk assessment and conservation management.”
The scientists investigated the effects of current exposure and the carryover effects of past insecticide exposure on the individual vital rates and population growth of the bee. “Bees in flight cages freely foraged on wildflowers, some treated with the common insecticide, imidacloprid, in a fully crossed design over two years, with insecticide exposure or no exposure in each year,” they wrote.
They found that “insecticide exposure directly to foraging adults and via carryover effects from past exposure reduced reproduction. Repeated exposure across two years additively impaired individual performance, leading to a nearly fourfold reduction in bee population growth.”
“Exposure to even a single insecticide application can have persistent effects on vital rates and can reduce population growth for multiple generations,” they wrote. “Carryover effects had profound implications for population persistence and must be considered in risk assessment, conservation, and management decisions for pollinators to mitigate the effects of insecticide exposure.
The 2018-2019 study took place on the grounds of the Harry H. Laidlaw Jr. Honey Bee Research Facility, located west of the central UC Davis campus.
The researchers tested only imidacloprid, a commonly used pesticide related to nicotine, and in exposures that bees would normally encounter in an agricultural field or orchard. The bees visited three species of wildflowers: lacy phacelia (Phacelia tanacetifolia), great valley phacelia (Phacelia ciliata), and purple Chinese houses (Collinsia heterophylla).
Any other adverse effects of the pesticide exposure? “We also saw effects of current pesticide exposure on offspring sex ratio, probability of nest initiation, and nest construction rate,” Stuligross said.
Financial Support. The study drew financial support from Stuligross' National Science Foundation Graduate Research Fellowship; her UC Davis Henry A. Jastro Graduate Research Award, and her UC Davis Ecology Graduate Research Fellowship, as well as from the UC Davis Department of Entomology and Nematology through the Harry H. Laidlaw Jr. Bee Research Facility and the Laidlaw Endowment.
The next step? “We are interested in studying how this type of pesticide exposure affects bees in a full field setting, where bees are exposed to multiple stressors simultaneously," she said.
Unlike honey bees, the reproductive rate of the blue orchard bee is low. A queen honey bee can lay about 2000 eggs a day in peak season, while the female blue orchard bee lays about 15 eggs a year.
Stuligross, who began her doctoral studies at UC Davis in 2016, holds a bachelor's degree in environmental studies (2014) from Earlham College, Richmond, Ind. “I am broadly interested in bee biology, population ecology, and understanding how bees interact with their environments in natural and managed ecosystems,” she says. “I use a combination of landscape, field cage, and lab experiments to study these interactions at different scales.”
Stuligross previously worked as a science educator at Carnegie Museum of Natural History, a research technician with Rufus Isaacs at Michigan State University studying bee communities in blueberry fields. I was also an undergraduate researcher with T'ai Roulston, Rosemary Malfi, and Wendy Tori studying bumble bee foraging, parasitism, and ecological niche modeling.
Stuligross and Williams assisted with the production of the KQED Deep Look video, "Watch This Bee Build her Bee-Jeweled Nest," posted Aug. 7, 2018. The video notes that most of the 4000 bees in North America are solitary. Mason bees, or "builder bees," build their nests with mud, and provision their nests with nectar and pollen for their offspring.
In nature, the blue orchard bees use hollow tubes, such as reeds. The UC Davis lab uses wood blocks or "bee condos" drilled with specially sized holes, each filled with a removable six-inch-long paper straw. Almond growers who manage blue orchard bees provide drilled wood blocks in their orchards. The bee condos are also popular among backyard gardeners.
More Information:
- Pesticides Can Affect Multiple Generations of Bees (UC Davis story by Amy Quinton)
- The Blue Orchard Mason Bee (U.S. Forest Service website, article by Beatriz Moisset and Vicki Wojcik, Pollinator Partnership)
- Imidacloprid Fact Sheet, National Pesticide Information Center
- Imidacloprid, Wikipedia
- Author: Kathy Keatley Garvey
Ah, Saturday, April 17. It's the 107th Annual UC Davis Picnic Day! What's a picnic without bugs?
This year's event, all virtual, is themed "Discovering Silver Linings," and you can do just that by watching the pre-recorded videos and by participating in the Zoom sessions. Check out the Picnic Day schedule of events which include entomological exhibits and talks from the UC Davis Department of Entomology and Nematology, Bohart Museum of Entomology and the UC Davis Graduate Student Association.
New additions to the line-up (featured on the Bohart Museum of Entomology website), involve what you could call "The good, the bad and the bugly." Blue orchard bees, tsetse flies and mosquitoes are spotlighted in UC Davis research-based videos created by KQED's Deep Look series and presented by PBS Digital Studios. Each runs about four minutes.
Here are the KQED productions:
- Watch this Bee Build Her Bee-Jeweled Nest, featuring blue orchard bees, the project of UC Davis doctoral student Clara Stuligross.
- A Tsetse Fly Births One Enormous Milk-Fed Baby, showcasing the work of medical entomologist Geoffrey Attardo, assistant professor, UC Davis Department of Entomology and Nematology.
- This Dangerous Mosquito Lays Her Armored Eggs--in Your House, involving the Aedes aegypti mosquitoes that the Attardo lab studies.
Clara Stuligross, Doctoral Student
They exposed the bees to the neonicotinoid insecticide imidacloprid, widely used in agriculture, and found that the combined threats—imidacloprid exposure and the loss of flowering plants—reduced the bee's reproduction by 57 percent, resulting in fewer female offspring.
Other scientists have conducted similar research on honey bees, but this is the first comparable research on wild bees in field or semi-field conditions. The blue orchard bee, nicknamed BOB, is a dark metallic mason bee, smaller than a honey bee. It is prized for pollinating almond, apple, plum, pear, and peach trees. California almond growers often set up bee boxes or "bee condos" for blue orchard bees to aid in honey bee pollination. In the wild, the bees nest in reeds or natural holes.
Update? "We are currently working on a follow-up study to investigate potential carryover effects of past insecticide exposure on the same bee population, as well as how repeated pesticide exposure over multiple years impacts bee population growth," Stuligross said today.
Geoffrey Attardo, Medical Entomologist-Geneticist 
What many people do not know: "Female tsetse flies carry their young in an adapted uterus for the entirety of their immature development and provide their complete nutritional requirements via the synthesis and secretion of a milk like substance," Attardo says.
Attardo led landmark research published Sept. 2, 2019 in the journal Genome Biology that provides new insight into the genomics of the tsetse fly. The researchers compared and analyzed the genomes of six species of tsetse flies. Their research could lead to better insights into disease prevention and control.
The Deep Look episode on mosquitoes, "This Dangerous Mosquito Lays Her Armored Eggs-- in Your House," deals with the ability of Aedes aegypti eggs to survive out of water. Wrote the producers: "The Aedes aegypti mosquito, which can transmit dengue fever and Zika, makes a meal of us around our homes. And her eggs are hardy. They can dry out, but remain alive for months, waiting for a little water so they can hatch into squiggly larvae."
- Author: Kathy Keatley Garvey
Lead author and doctoral student Clara Stuligross teamed with her major professor, pollination ecologist Neal Williams of the UC Davis Department of Entomology and Nematology, to publish Pesticide and Resource Stressors Additively Impair Wild Bee Reproduction, in the journal Proceedings of the Royal Society B.
They exposed the bees to the neonicotinoid insecticide imidacloprid, widely used in agriculture, and found that the combined threats—imidacloprid exposure and the loss of flowering plants—reduced the bee's reproduction by 57 percent, resulting in fewer female offspring.
Of the two stressors—food scarcity and pesticide exposure—pesticide exposure showed the great impact on nesting activity and the number of offspring produced, they said.
Other scientists have conducted similar research on honey bees, but this is the first comparable research on wild bees in field or semi-field conditions.
The blue orchard bee, nicknamed BOB, is a dark metallic mason bee, smaller than a honey bee. It is prized for pollinating almond, apple, plum, pear, and peach trees. California almond growers often set up bee boxes or "bee condos" for blue orchard bees to aid in honey bee pollination. In the wild, the bees nest in reeds or natural holes.
“Bees and other beneficial insects experience multiple stressors within agricultural landscapes that act together to impact their health and diminish their ability to deliver the ecosystem services on which human food supplies depend,” Stuligross and Williams wrote in their abstract. “Disentangling the effects of coupled stressors is a primary challenge for understanding how to promote their populations and ensure robust pollination and other ecosystem services.”
To study the survival, nesting and reproduction of the blue orchard bee, they set up nesting females in large flight cages, some with high densities of wildflowers and others with low densities that were treated “with or without the common insecticide, imidacloprid.” Bees are commonly exposed to insecticides when they forage on treated flowers.
“Pesticides and resource limitation acted additively to dramatically reduce reproduction in free-flying bees,” they wrote in their abstract. “Our results emphasize the importance of considering multiple drivers to inform population persistence, management, and risk assessment for the long-term sustainability of food production and natural ecosystems.”
Key factors in affecting bee reproduction are the probability that females will nest and the total number of offspring they have. The UC Davis research found that pesticide-exposed and resource-deprived female bees delayed the onset of nesting by 3.6 days and spent five fewer days nesting than unexposed bees.
They found that only 62 percent of pesticide-exposed bees produced at least one daughter compared to 92 percent of bees not exposed to pesticides.
The research, accomplished in the spring of 2018 on the grounds of the Harry H. Laidlaw Jr. Facility west of the campus, drew support from a UC Davis Jastro Research Award, a UC Davis Ecology Graduate Research Fellowship, a National Science Foundation Graduate Research Fellowship, and the UC Davis bee biology facility
The blue orchard bee bee is one of the few native pollinators that is managed in agriculture. North America has 140 species of Osmia, according to a Pollinator Partnership (PP) article in a U. S. Forest Service publication, authored by entomologist and PP member Beatriz Moisset and PP director Vicki Wojcik. “Mason bees use clay to make partitions and to seal the entrance,” they wrote. “This unique mud-building behavior leads to their common designation as mason bees. Honey bees are very important to commercial agriculture, but native bees like the blue orchard bees are better and more efficient pollinators of native crops.”
Imidacloprid, a systemic insecticide that acts as an insect neurotoxin, is used to control sucking insects, termites, some soil insects and fleas on pets, according to National Pesticide Information Center. It mimics nicotine, toxic to insects, which is naturally found in many plants, including tobacco. More than 400 products for sale in the United States contain imidacloprid.
