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Bumble Bee Queens Slower to Start Colonies After Neonic Exposure

Bombus impatiens queen

Bumble bee queens, such as the Bombus impatiens queen shown above, forage in the spring as they initiate new colonies. New research shows that exposure to small amounts of the neonicotinoid insecticide imidacloprid during that period can delay a B. impatiens queen’s nest initiation and brood emergence—if the queen survives the exposure at all. (Photo credit: Flickr/USGS Bee Inventory and Monitoring Lab)

Spring is an important period for bumble bees, as that’s when new colonies get their start. When a solitary bumble bee queen emerges from hibernation, she initiates a nest and then does the foraging work herself, until her first offspring hatch, develop into workers, and relieve her from all duties but egg laying. Thus, should any harm befall the queen in this early period, it can have ripple effects on the health of the developing colony.

According to a new study published last week in Environmental Entomology, queens of the bumble bee species Bombus impatiens that encounter the neonicotinoid insecticide imidacloprid in that foraging period show delayed nest initiation and brood emergence—if they survive the exposure at all.

Researchers at the University of Minnesota conducted an experiment in which they exposed B. impatiens queens to imidacloprid at levels between 1 and 25 parts per billion (ppb) in a sugar syrup, to “reflect a typical flower bloom period during which bees may become exposed to neonicotinoids when foraging on contaminated nectar and pollen in the environment.” They then measured how many queens survived, how long they took to start a nest, and how many eggs they laid.

Queens treated with the insecticide at 1, 10, and 25 ppb died in greater numbers, and sooner, compared to untreated queens (though no significant difference was found at the 5 ppb treatment level). Meanwhile, though untreated queens began laying eggs between 13 and 20 days after the experiment began, queens exposed to imidacloprid were slower to begin their nests, some taking several weeks longer, “which suggests a possible dose-dependent delay and recovery by queens once exposure ended,” according to the authors of the study, Judy Wu-Smart, Ph.D., a doctoral candidate at the University of Minnesota at the time of the study and now an assistant professor and extension specialist at the University of Nebraska-Lincoln, and Marla Spivak, Ph.D., distinguished McKnight professor at Minnesota.

Bombus impatiens queens and nests

Researchers at the University of Minnesota measured the nest development of Bombus impatiens queens that had been exposed to small amounts of the neonicotinoid insecticide imidacloprid. They found that queens exposed to amounts that would equate to what queens in the wild might encounter in flowers contaminated by drift from nearby agricultural fields showed slower nest initiation and brood development than queens not exposed to the insecticide. (Photo credit: Judy Wu-Smart, Ph.D.)

Wu-Smart says she and Spivak were surprised to see that some of the queens (35 percent) died at the lowest exposure level, 1 ppb. “Previous studies with bumble bees examined the impacts of neonics on worker bees and or queenless microcolonies of bumble bees. In these studies, low doses, such as the 1 ppb we used, did not cause mortality in worker bees as it did in our study on queens, indicating that queens may be more susceptible than worker bumble bees,” says Wu-Smart.

Other studies have shown that the effect of neonicotinoids can vary from species to species, as well. “Therefore,” Wu-Smart says, “non-target risk assessments for pesticides need to consider species- and caste-specific differences when measuring toxicological impacts on physiological and behavioral responses.”

Pesticides are among a variety of contributing factors to declining bee populations in North America. Wu-Smart says the results of this research further underline the importance of minimizing non-target exposure of pesticides such as neonicotinoids.

“This study illustrates a particular time in the season, during spring nesting, in which reproductive queen bees may be more vulnerable to neonicotinoid exposure. Therefore, mitigation actions should focus on reducing exposure risk during this time,” she says.


  1. Are “mitigation actions to reduce exposure” really needed considering that bumblebees and other pollinators can be filmed in abundance along the perimeter margins of corn and soybean fields in Minnesota (where the researchers work) that were grown from neonic coated seeds? Example:

    • Just because pollinators are seen near a corn or soybean field doesn’t mean they are not being impacted by pesticide exposure in those areas. Determining what the effects may be is the role of the scientists, hence this research study.

  2. I live in Florida and grew up many moons ago in Michigan. thus my memories ae limited. u his question quickly occurred to me. What would a farmer be spraying with Imidacloprid in early spring?

    • Nothing is sprayed. There are various seed treatments some including Imidacloprid (most have a Neonicotinoid, not necessarily Imidacloprid)) which create the problem as the dust from the planting process moves to early blooming flowers like Dandelions. Bees collect the pollen and there you go.

  3. John, they are now using methods that create far less dust. plus there is almost nothing for the little dust now created to settle on that early. That is my point. They are not spraying.

    • Early spring blooming trees and shrubs (e.g. willow, maple, lilac) and herbaceous flowers like dandelion are critical forage for pollinators because there is little else to collect pollen and nectar from at that time. So the pesticide-laden dust that drifts and settles on them during the planting process is concerning from that standpoint alone (the little forage available may be contaminated). Plus, systemic insecticides may move through soil and water to nearby flowering vegetation, and come in contact with pollinators in that way.

      • “laden” I doubt it. They have reduced the dust produced. Until you have examples from real life that is speculation. The tiny amounts on seeds aren’t real likely to move laterally. Remember that early flowering stuff isn’t in the fields and gravity pulls stuff down. not sideways.

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