Common Insecticide Linked to Honeybee Colony Collapse

In the fall of 2006, etymologists faced a distressing situation: bee colonies were dying off at unprecedented rates. Over the winter of 2006, bee colonies continued to decline, and beekeepers reported losses of between 30 to 90 percent of their hives. Though some die-off is expected to occur over the winter, these rates were still much higher than expected. Scientists were baffled. What was behind this drastic loss of bee colonies? Can anything be done to solve this crisis?

Bees are important pollinators for a number of crops. (Photo credit: B.A.E. Inc./Alamy)

The Importance of Bees

Bees do much more than produce honey. In fact, bees are an essential part of the pollination process for more than 100 food crops. These insects are particularly important pollinators for nut, fruit, and vegetable crops.

The California almond industry alone requires the importation of more than 50 percent of the entire honeybee population in the United States! Due to their important agricultural role, the loss of bees could potentially decimate crop production and the agricultural industry that depends upon them. According to the United States Department of Agriculture (USDA), bees add more than $15 billion in value to a variety of crops they pollinate.

Though the colony loss in late 2006 was astonishing, bee colonies have actually been on the decline since the 1980s. Scientists point to the introduction of new pathogens and pests as explanations for the decline in bee colony health. When a high number of bee colonies are imported to pollinate a crop such as almonds in California, it is quite easy for pathogens and other ailments to pass from one colony to another. Stresses from moving a colony from one place to another has also been implicated in increased colony losses since the 1980s as well.

Colony Collapse Disorder

Colony Collapse Disorder, or CCD, is the name scientists have given to the current situation faced by bee colonies. When the initial collapse became apparent in 2006, scientists weren’t quite sure what was behind the disorder. In fact, multiple hypotheses abounded. According to the Agriculture Research Service (ARS) Bee Research Laboratory in Beltsville, Maryland, there were four possible explanations. These causes included pathogens, parasites, environmental stresses such as pesticides, and management stresses, such as a lack of proper nutrition sources for the bees.

In 2007, ARS scientists began testing these various hypotheses. In their research (which is on-going), the scientists collected bees from both healthy colonies and CCD-affected colonies. They then screened the collected bees for the presence of both new and known pathogens. The scientists discovered that bees from the colonies affected by CCD had a higher rate of infection by Nosema ceranae, a fungal pathogen. However, this higher rate was not considered statistically significant–meaning that Nosema could not be implicated as the sole explanation for colony decline. Further analysis showed that the incidence of bees that had high fungal-pathogen loads combined with infection by several RNA viruses from the Dicistroviridae family was a clear indicator of imminent colony collapse.

Nosems ceranae infects bees through the fecal-oral route. When bees ingest the fungal pathogen, it embeds itself into the bees gut lining. Scientists hypothesize that a greater number of fungal pathogens in the bees gut lining compromises the bees health, and allows subsequent RNA virus infections to overwhelm the bee, thus killing it.

However, a new study from the Harvard School of Public Health indicates that the likely culprit in worldwide honeybee colony declines is actually imidacloprid, a popular pesticide. The results of the study, led by Chensheng Lu, an associate professor of environmental exposure biology at Harvard, will be published in the June issue of the journal Bulletin of Insectology.

Imidacloprid is a neonicotinoid, a class of insecticides that was developed in the 1980s and introduced into common use in the early 1990s. Imiadocloprid is one of the most widely-used insecticides and is utilized to combat soil, timber, seed, and animal pests. It is also used as a treatment against pests that attack cereal, cotton, grain, potato, rice, fruit, and vegetable crops. The impact of neonicotinoids on bee colonies has actually been known for quite a while. Several European countries have banned or limited the use of this class of insecticides–due to its observed effects on honeybees–soon after it was introduced in the 1990s.

According to the Harvard researchers, honeybees can be exposed to imidacloprid in two ways: either through nectar from plants that have been treated with imadocloprid or through the high-fructose corn syrup that beekeepers use to feed their honeybees. (Imadacloprid is found in corn syrup because most of the corn grown in the United States has been treated with this insecticide since 2005.)

The significance of bees to agriculture cannot be underestimated, Lu said in a press release about the new study. And it apparently doesn’t take much of the pesticide to affect the bees. Our experiment included pesticide amounts below what is normally present in the environment.

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