As if bees need any more hazards to worry about, now add fungicides to the list of culprits for so-called colony collapse disorder.

A growing body of evidence shows that a matrix of factors, not just one particular chemical or disease, is to blame for massive bee deaths in Europe and North America over the last few years. Scientists have pointed to everything from genetics to corn syrup as threats to pollinators. In some cases, widespread colony deaths have wiped out up to 30 percent of the yearly bee population since 2006.

Research released last month showed for the first time that fungicides appear to increases a bee's susceptibility to a virulent gut parasite called Nosema – one of many diseases linked to colony collapses.

It's Complicated

Jeffery Pettis, an author of the study and lead researcher for the U.S. Department of Agriculture's research service, said researchers tested bees exposed to pollen that was gathered near crops like blueberries, cucumbers and watermelon, and detected 35 different pesticides, including high levels of fungicides. The latter turned out to be a significant risk factor in bees that suffered from Nosema.

"The fungicide exposure part was surprising in that fungicides are usually labeled as being safe for bees, and you can apply them during bloom and all that," he said. "We highlighted the fact that fungicides may not be as safe as previously thought."

Significantly, the same study looked at real-world doses of pesticides in the bees they studied, rather than exposing bees to arbitrary amounts of a single compound that might not reflect exposure in the field. Critics have slammed previous studies on pesticides for using doses higher than bees would normally encounter.

"It's a complex organism that we're dealing with. The media and the public love it when we can say 'all pesticides are what's killing hives.' But it's probably a little more complicated than that."

Pettis said the study suggests more research is needed for one widely used fungicide called chlorothalonil. He said a 2009 study revealed that bees will even detect pollen contaminated with the chemical, sealing off cells in the hive that contain it with propolis.

We highlighted the fact that fungicides may not be as safe as previously thought.

Call To Action

Emily Marquez, a staff scientist with the Pesticide Action Network North America, said the research supports a growing consensus that bee health is compromised by contact with a "chemical cocktail" that includes pesticides.

"The science linking bee declines and pesticides is complex, but it is clear," she said. "Given the incredibly important pollination services bees provide in support of our food system and agricultural economy, protecting bees should be a priority. And yet, EPA is still stuck."

Marquez called for restrictions on bee-harming pesticides for crops that depend on pollinators, and for the Environmental Protection Agency to step up its research on those chemicals, as well as alternative pest control methods.

Bees In Congress

The Congressional Research Service rolled out a 24-page report to update lawmakers on recent studies into causes of bee colony deaths. The primer covers mostly basic background knowledge, but also identifies potential economic costs to the nation's agriculture industries, citing a Cornell study in 2010 that estimated the annual impact of commercial honey bees and other insect pollinators to be about $16.4 billion.

Last month representatives Earl Blumenauer and John Conyers, Jr. introduced a bill that would suspend the use of pesticides known to affect bee health, and calls for annual updates on the issue from the Environmental Protection Agency and the Department of the Interior. The Saving America's Pollinators Act has been referred to the House Agriculture Committee.

Also last month, the EPA issued new regs for pesticide labels that will ban the use of four key neonicotinoid pesticides in areas where bees pollinate.

Read More:

• University Researchers Find Pesticides, Fungicides Can Contribute To Deadly Bee Stomach Infection (The Diamondback)
• Crop Pollination Exposes Honey Bees To Pesticides Which Alters Their Susceptibility To The Gut Pathogen Nosema ceranae (PLOS One)
• Bee Health: Background and Issues for Congress (pdf) (Congressional Research Service)