Dangers Facing Honeybees
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.