Honeybee Colony Collapse Disorder Not Only Affected by Pesticides


Pesticides have been a central focus in the issue of Colony Collapse Disorder (CCD) in Europe, and recent research has confirmed its harmful effects in the U.S. A study of the disorder out of Harvard School of Public Health (HSPH) has recently identified two neonicotinoid-based pesticides as the likely culprits of the wide-spread honeybee colony collapses in the U.S. Published May 9, 2014, the follow-up study has received a great deal of push back from manufacturers of the pesticides, most notably among them the German giant Bayer CropScience. Bayer decried flaws in the Harvard study they claim downplayed the role of parasites in CCD. The same HSPH study published this month also suggested that climatic factors, such as abnormally long and harsh winters, contribute to CCD. The problem of CCD in the US may not be as simple as a conflict of interests between pesticide manufacturers and disgruntled agriculturalists. What appears to be at play is a synergy of all the factors suggested: a killer cocktail for honeybees composed of harsher-than-normal winters, exposure to neonicotinoid-based pesticides, and colony susceptibility to malevolent parasites.

Chensheng Lu, the lead author of the HSPH study released this May, said the findings support the same conclusions that were observed by his team in Massachusetts honeybees in 2012. Both studies, according to Lu, showed that neonicotinoid pesticides were “highly likely” to be responsible for CCD in honeybee populations. Lu stated that they observed higher mortality rates in the 2012 study, adding, however, that the higher number was likely a result of the particularly harsh winter that hit central Massachusetts that year. He added that more research is needed in order to warrant an outright ban on the pesticides, a ban that the European Commission has already found prudent and initiated as of last year.

Bayer responded by pointing out what they found to be “seriously flawed” with the study. The main issue was the bees in the study were subjected to over 10 times the amount of neonicotinoids than they would normally be exposed to in a natural environment. Bayer scientists pointed out that CCD is to be expected when colonies are subjected to such a high level of neonicotinoids; however, honeybees do not encounter such concentrated neonicotinoid levels in the wild, they said. Bayer scientists urged HSPH researchers to consider more seriously the impact that parasites have on honeybee colonies.

One parasite in particular, Nosema ceranae, has been a known culprit in CCD since the mid 1990s, and according to a report released this May by the Society For Applied Microbiology, can exacerbate the collapse of a colony already exposed to neonicotinoid pesticides. The synergistic effect, according to the report, is a cause for much concern because it was observed to occur in honeybee populations that were exposed to only “sublethal” doses of neonicotinoid pesticides.

To make matters worse, research published in the Public Library of Science last year claimed that the only approved treatment for N. ceranae, an antibiotic called fumagillin, does not stand up to the parasite effectively enough to protect honeybee populations. In fact, the research found that the current application process for fumagillin exacerbates N. ceranae infection instead of suppressing it.  As the fumagillin subsided in the infected honeybees, researchers observed a sharp increase in N. ceranae emergence that was not found in infected honeybees that were not given the antibiotic.

According to Beeologics, an international limited liability firm that focuses on protecting and restoring honeybee health, there are “no current effective preventative measures” to combat CCD to date.

When considering the combination of lethal factors, the harsher winters, malevolent parasites, and neonicotinoid-based pesticides, all bring about a synergistic effect that ensures Colony Collapse Disorder in U.S honeybee populations. Although harmful in their own right, neonicotinoid-based pesticides are not solely responsible for the recent incidence of CCD. Rather, winter climatic conditions and ineffective antibiotic treatments for parasites play a large, synergistic role. One thing that all the studies involved agree on is the need for further study.

By Courtney Anderson

Public Library of Science
Wiley Online Library
Science Recorder

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