"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.
- 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
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.
During the day, European wool carder bees (so named because the females collect or "card" plant fuzz for their nests) forage on our catmint and lamb's ear.
These bees, Anthidium manicatum, are about the size of a honey bee, but with striking yellow and black markings. From Europe and fairly new to the United States, they became established in New York in 1963, and then began spreading west. Eventually this exotic species made its way to California. Bee scientists first identified it in California (Sunnyvale) in 2007.
"The females nest in convenient cavities such as old beetle holes and hollow stems," according native pollinator specialist Robbin Thorp, emeritus professor entomology at UC Davis. Its plant preferences include lamb’s ear (Stachys byzantine, in the mint family Lamiaceae), a perennial grown for its fuzzy, silvery gray-green foliage.
At night, the females return to their nests. But for the boys, it's the boys' night out.
The "boy bees," as Thorp calls them, "sleep wherever they can."
Every night and early morning, we see a male sleeping inside one of our native bee condos. This particular condo, located several feet above our catmint patch, is drilled with "large" holes to accommodate the blue orchard bee (Osmia), a mason bee. The holes really aren't that large, but they are compared to our bee condo for the smaller leafcutting bees.
For awhile, our mason bee condo drew nothing but earwigs. Not one blue orchard bee (BOB).
Now we have a exotic species sleeping in a native bee condo.
What a treat! At least we have one tenant!
When we took his picture in the early morning, the European wool carder bee didn't budge. Guess he's saving his energy to chase the girls around in the catmint patch.