News

Bee Alert! Honey bees at risk from fungicides

July 31, 2013

Photo Bob Peterson

BEE ALERT! New research published last week has found that fungicides are also implicated in declining bee populations.

Published in the online journal PLoS ONE, the research by Pettis et al found that honey bees returning to their hives from crop pollination, carrying feed pollen for the colony, were bringing with it a truly alarming cocktail of pesticides and fungicides, with an average 9.1 different types per sample. Two pollen samples even contained one pesticide each at a concentration higher than the median lethal dose, and one cranberry field produced pollen with 21 different pesticides in it.

While there is evidence linking neonicotinoid pesticides with bee Colony Collapse Disorder, in this study, they found that fungicides like chlorothalonil, pyraclostrobin and myclobutanil could be as much to blame for bee deaths. Myclobutanil is found in many home garden fungicides.

While fungicides have been thought to have minimal effect on bees, those that were fed in a laboratory with collected pollen, which analysis showed contained these fungicides, had twice the infection rate when exposed to Nosema ceranae, a gut parasite that causes bee death and colony collapse. The Nosema infection rates of the fungicide-exposed bees were compared to control populations fed artificial pollen or certified pesticide free pollen. The researchers found that fungicide exposure increased bee gut cell mortality, allowing the Nosema parasite to proliferate. In pollen high in pyraclostrobin, the infection rate was nearly 3 times higher.

The researchers also found that despite being rented to pollinate specific agricultural crops, the honey bees foraged widely, carrying back pollen from many wildflowers and weeds and sometimes nothing at all from the target crop. Interestingly, they also found that nearly all pollen came from ‘Old World’ crops, alongside which the bee had evolved, with virtually no pollen from crops which had originated in the Americas.

From the study’s Discussion section:

“The combination of high pesticide loads and increased Nosema infection rates in bees that consumed greater quantities of the fungicides chlorothalonil and pyraclostrobin suggest that some fungicides have stronger impacts on bee health than previously thought. Nosema infection was more than twice as likely (relative risk >2) in bees that consumed these fungicides than in bees that did not. Research on the sub-lethal effects of pesticides on honey bees has focused almost entirely on insecticides, especially neonicotinoids [54]. In our study, neonicotinoids entered the nest only via apple pollen. However, we found fungicides at high loads in our sampled crops. While fungicides are typically less lethal to bees than insecticides (see LD50 values in Table 2), these chemicals still have potential for lethal [55] and sub-lethal effects. Indeed, the fungicides chlorothalonil (found at high concentrations in our pollen samples) and myclobutanil increases gut cell mortality to the same degree as imidacloprid [56], an insecticide with numerous sub-lethal effects (e.g. [21], [57])”

The researchers also stated that “published LD50 values may not accurately indicate pesticide toxicity inside a hive containing large numbers of pesticides. Research looking at additive and synergistic effects between multiple pesticides is clearly needed.”

Citation: Pettis JS, Lichtenberg EM, Andree M, Stitzinger J, Rose R, et al. (2013) Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae. PLoS ONE 8(7): e70182. doi:10.1371/journal.pone.0070182

[Many thanks to Helen McKerral for sending in information about this research]