Last year, we reported on Colony Collapse Disorder, a condition which causes worker bees to abandon their hives, wiping out up to a third of U.S. honey bee population each year. CCD has been a growing cause of concern since 2007, when it first became widely noted. Honey Bees pollinate $15B worth of food each year including apples, berries, cantaloupes, cucumbers, alfalfa, and almonds, so the potential impact of CCD on both our food supply and economy could be devastating.
Because of the seriousness of this issue, there has been a lot of research on honey bees, and on CCD over the past several years. The results have indicated that there is no one cause of CCD, but rather a combination of stressors, including pesticides, mites, and viruses, along with the heavy travel schedule of commercial bees, have combined to weaken bee colonies, and make there more susceptible to disease and parasites.
Two recent articles in the online journal PLoS, One describe the results of recent research, again highlighting the combination of causes for CCD. In the first one “A New Threat to Honey Bees, the Parasitic Phorid Fly Apocephalus borealis“, researchers document how female phorid flies deposit larvae into the abdomen of honey bees. Bees display abandonment behavior, and then die. with mature larvae exiting the honey bee between head and thorax. The result of the parasite?
In the case at hand, perhaps A. borealis manipulates the behavior of honey bees by changing a bee’s circadian rhythm, its sensitivity to light or other aspects of its physiology….
…Our data clearly show that phorid-parasitized bees demonstrate the unusual behavior of abandoning their hives at night. However, we can’t exclude the possibility that some parasitized bees also abandon their hive during normal foraging times and die at some distance from the hive.
So this is it, right? We have found the reason for CCD? Now all we have to do is learn how to protect the bees from these flies (not necessarily any easy thing) but at least we know what to do, right?
Well, not so fast. CCD has been a problem for several years, and the phorid fly, although known as a parasite to bumble bees, has not been observed in honey bees. As the authors note:
Honey bees are among the most studied insects in North America due to their importance to agriculture. The meticulous attention given to honey bees by humans suggests that phorids would have been detected sooner had the host shift occurred long ago, especially since detection of the parasite does not require sophisticated techniques. Observation of dead bees over as little time as five days should detect phorid presence. Furthermore, honey bees have inhabited areas adjacent to electric lights for at least a century, yet we know of no reports of large numbers of honey bees aggregating around lights until recently. This latter point suggests that, even if the flies were present in low numbers in honey bee colonies in the past, something has happened recently that has increased densities making phorids an emerging threat.
So, if the phorid fly represents a new threat for the bees, what have we learned about other causes of CCD? There is evidence that one of the main culprits is the use of insecticides, particularly the class of insecticides known as neonicotinoids. These insecticides are highly toxic, persistent (meaning that they last a long time in the environment) and heavily used in many crops, particularly corn (maize). In another paper published by PLoS One “Multiple Routes of Pesticide Exposure for Honey Bees Living Near Agricultural Fields” researchers reported that a series of mechanisms resulted in lethal exposures for the bees. The researchers focused on Maize, because it
…represents the largest single use of arable land in North America. Maize planting reached unprecedented levels in the US in 2010 (35.7 million hectares , and is expected to increase.
And almost all of the planted maize is coated with neonicotinoid insecticides. (Organic production accounts for 0.2% of acreage). The seed is coated with one or more insecticides, and then mixed with talc to make automated planting easier. Some of the results.
- Insecticides were found in the soil
- Clothianidin was found on all the dead and dying bees we sampled, while the apparently healthy bees we sampled from the same locations did not contain detectable levels of clothianidin
- Soil collected from areas near our test site revealed that neonicotinoid insecticide residues were present in all samples tested, with clothianidin occurring in each field sampled. (even fields that were not planted that year)
- Many of the same compounds were present in maize grown from treated seed.
- Both soil and dandelion flowers obtained from the fields closest to the affected apiary (soybeans in 2010, unplanted when sampled in 2011) contained clothianidin, therefore clothianidin in/on the dandelions could have resulted from translocation from the soil to the flower, from surface contamination of the flowers from dust, or a combination of these two mechanisms
- Clothianidin and other pesticides were found in the pollen of nearby hives.
There is really nothing that new in our conclusion. Mono crop agriculture and heavy insecticides weaken parts of the eco system. More organic agriculture, a greater mix of crops, and integrated pest control are crucial