Threats to Honeybees: Colony Collapse Disorder, Pesticides, Parasites & More

What's Bugging the Honey Bees?

Anyone skimming headlines about the “world-wide honeybee crisis” could be forgiven for believing we’ve all but lost the fight to save the planet’s pollinators. Read beneath the headlines and one becomes more optimistic, however, because research into the plight of bees has unearthed fascinating insights into their behavior and health, and the environmental pressures affecting them.

Hundreds of billions of dollars’ worth of plants need to be pollinated each year to produce the food, beverages, fibers, spices and medicines upon which we depend. There is no doubt that the pollinators we need the most – bees, ants, wasps and butterflies – are currently in broad decline across the globe, but there may yet be room for hope.

Dangers Facing Honeybees

Colony Collapse

Though Europe reported a significant drop in the number of managed honeybees and native bees over the last few decades, it wasn’t until 2006, when “Colony Collapse Disorder” (CCD) was first described that most North Americans began to pay attention to the emerging honeybee crisis. CCD (“Honey Bee Colony Depopulation Syndrome” in Europe) has been identified as a combination of events that result in the death of a bee colony.

While researchers originally looked for a single cause, the inquiry has now broadened, and the research exploded, beyond CCD. Studies over the past few years have identified a number of threats, prompting Adam Vanbergen, the leader of a review of pollinator health published in April of this year, to state, “There is no single smoking gun behind pollinator declines; instead there is a cocktail of multiple pressures that can combine to threaten these insects.” The report expanded on that by concluding “A suite of interacting pressures is having an impact on pollinator health, abundance, and diversity. These include land-use intensification, climate change, and the spread of alien species and diseases.”

Pollution & Pesticide

In an effort to identify (and ultimately manage) some of the pressures facing pollinators, scientists around the world have focused on both the pollinators, and their environment. Researchers from the University of Maryland and the U.S. Department of Agriculture (USDA) collected and analyzed pollen from honeybee hives and found, on average, nine different agricultural chemicals, including fungicides, insecticides, herbicides and miticides in the samples. Sub-lethal levels of several agricultural chemicals were present in every sample, with one sample containing 21 different pesticides. And there is growing evidence that even sub-lethal doses of pesticides may weaken bees and make them more susceptible to other threats.

Scientists from Royal Holloway found “when bees are exposed to low levels of neonicotinoid pesticides, which do not directly kill bees, their behaviour changes and they stop working properly for their colonies.” (Neonicotinoids are currently banned in Europe.)


Chemicals are only one of the threats facing honeybees. The parasitic mite Varroa destructoris has been identified as a “significant contributor to CCD. Varroa sucks the blood of larval and adult bees leaving them weakened and reducing the ability of their immune systems to fight off infections.” These tiny mites can also spread viral infection between hosts. Last year, researchers at the University of Sheffield discovered that the Varroa mite caused the deformed wing virus to proliferate in honeybee colonies, an association “now thought to contribute to the world-wide spread and probable death of millions of honeybee colonies.”

Disease & Disorders

Another, long-term, study of honeybee health found that a little-understood disease the researchers called “idiopathic brood disease syndrome” (IBDS), which kills off bee larvae, was the largest risk factor for predicting the death of a bee colony. The study also found that the occurrence of a “queen event” was also influential. According to the researchers, “honeybee colonies have only one queen. When a colony perceives something wrong with its queen, the workers eliminate that queen and try to replace her. This process is not always smooth or successful.”

Examining different variables, a research team from North Carolina State University, the University of Maryland, and the USDA showed that genetic diversity is enormously influential in honeybee populations. The more mates a queen has had, the higher the genetic diversity in the colony, and the more likely the colony is to survive.


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Research continues to identify threats, test potential treatments, and develop breeding and management solutions, but it has been suggested that to dampen the effect of honeybee losses, there should be a renewed focus on wild pollinators as an “insurance policy.” The economic value of pollination is often credited solely to honeybees, but a number of studies have found that while honeybees are essential pollinators in large scale plantations, for some crops, a mix of wild bees and honeybees is best. A recent study showed that the pollination effectiveness of honeybees in California almond orchards, for example, was greater in the presence of other bees.

How can an average homeowner leverage the research to help out their local pollinators? Here are a few things you can do in your own backyard:

  • Create a pollinator-friendly yard by providing water, and by growing flowers, shrubs, and trees with overlapping bloom times to help pollinators across the seasons.
  • Reduce lawn grass and use native plants adapted to local soils, climate, and pollinators. Provide a place for growing pollinators by leaving patches of bare ground and brush piles, and planting caterpillar host plants.
  • Reduce pesticides. Pesticides, especially insecticides, are harmful to pollinators, and herbicides reduce potential food sources by removing flowers from the landscape.

For more information visit the Pollinator Conservation Resource Center.


  • The Xerces Society (n.d.). Bring Back The Pollinators Campaign. Retrieved October 9, 2013, from
  • Royal Holloway, University of London (2013, October 7). Stress a key factor in causing bee colonies to fail. ScienceDaily.
  • North Carolina State University (2013, March 4). Researchers identify queens, mysterious disease syndrome as key factors in bee colony deaths. ScienceDaily.
  • Pensoft Publishers (2013, January 14). Two new studies show why biodiversity is important for pollination services in California almond. ScienceDaily.
  • North Carolina State University (2013, June 17). Genetic diversity key to survival of honey bee colonies. ScienceDaily.
  • University of Maryland (2013, July 24). Common agricultural chemicals shown to impair honey bees’ health. ScienceDaily.
  • Pensoft Publishers (2012, August 17). Wild pollinators support farm productivity and stabilize yield. ScienceDaily.
  • Center for Ecology & Hydrology (2013, April 22). Cocktail of multiple pressures combine to threaten the world’s pollinating insects. ScienceDaily.
  • University of Sheffield (2012, June 7). Highly contagious honey bee virus transmitted by mites. ScienceDaily.