UPDATE 1/30/12: Yet another study implicating Neonicotinoid insecticides. This time the study looks at sub lethal levels of imidacloprid fed in spiked pollen substitute patties on the susceptibility of newly emerged bees to nosema infection. There is clear evidence that although the bees themselves have an undetectable level of insecticide present, the ones fed contaminated pollen had higher levels of nosema spore counts 12 days after being exposed to the pathogen. (Click on the links for the original papers.)
A study just out from Purdue University researchers adds to the damning evidence that neonicotinoid insecticides are killing our honeybees and native insect pollinators. Neonicotinoid systemic insecticides are some of the most toxic substances to bees that were ever invented. At the recommended application level, the amount of clothainidin on a single corn kernel has enough toxicity on contact to kill all of the bees in strong colony. If the bees ingested the toxin, that single kernel’s worth of insecticide could kill all the bees in a dozen colonies. Because this stuff is so toxic, the only allowed uses of some of these substances has been as seed treatments where the insecticide is less accessible to bees. The Purdue study showed that despite the fact that the insecticide is buried with the seed, the bees can still get substantial exposure. Insecticide was found in corn pollen that bees were working as well as in dandelion flowers growing in fields being planted with treated seed, and more generally in the soil where crops with treated seed were grown before. Tests showed pesticide residue in stored pollen and in poisoned bees found at affected hives during corn planting activity. Contaminated talc, used to keep the seed flowing through the planting machines, is suspected as one way bees are contaminated as the talc is blown from the machines into the environment.
The problem is that there is no place for bees in America to hide. Virtually all of the corn seed planted in this country is treated with clothainidin, as are soybeans, and many other crops. If a field is planted in a commercial agriculture crop, chances are good the seed was treated with one variety of neonicotinoid or another. In the farm belt, fields stretch from fence-row to fence-row, mile upon mile with very little native habitat for bees or native insect species. Honeybees placed near these fields are likely to suffer nutritional stress because of the lack of variety of pollen sources as well as low-level insecticide poisoning. Still missing are good studies on developmental effects when the brood is fed contaminated pollen. (But check out the UPDATE!)
However, it’s unlikely that the neonicotinoids alone are responsible for honeybee colony collapse (CCD) that has plagued beekeepers since about the time that these new insecticides began being used heavily. Rather, the picture emerging is one of a combination of stresses and pathogens that drive the colony to collapse. As usual, one of the best sources for information on honeybee health and sickness is Randy Oliver’s Scientific Beekeeping site. In the last year he has had a series of articles on Sick Bees, printed originally in the American Bee Journal, that are worth spending time digesting. The picture Randy paints is one where a multitude of viruses, some recently introduced and some just part of the biological milieu that is a honeybee colony, become deadly to the colony when the bees are also infected with varroa and/or nosema. Poor nutrition or pesticide poisoning can push marginal colonies with such infections over the edge.
My bees are hunkered down for the winter now. When we get a warm day I still see them testing the weather in the afternoon. The filbert trees are already providing a bit of pollen if the bees can get it, but more likely they will just sit tight for another month. Now is when diseased colonies will finally succumb to the cold. Hives without sufficient numbers can no longer maintain a warm cluster, and the cold bees become even more susceptible to disease, accelerating the losses. I occasionally put my ear to a hive and give it a sharp rap with my knuckles and listen for the response of the bees in the cluster. The mite drop boards also give an idea of how large the cluster is by the extent of the debris field.
I gave my hives this cursory check this morning, and much to my dismay, it looks like the best producer last year is going down; barely a buzz and only a small amount of debris on the board. I checked a few dead bees with the microscope, but no sign of nosema. In all likelihood a virus is the proximate cause of their downfall. It’s another case of the now all-too-familiar CCD symptoms. I’ll just keep my fingers crossed that my other hives make it to spring.