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| Megachile xylocopoides S.Reeve |
I remember the honeybees of my childhood, they were so numerous they were deafening. Now, I go out into the yard, and I see one, maybe two, on a plant (Eriogonum fasciculatum) that, a few years ago, had hundreds. But people forget, and many, younger than me, think this dearth is normal. Back when I was a kid I marvelled at nature and found it everywhere: salamanders under every rock, bees crowding the flowering plants fighting for access to pollen and nectar, pollywogs in any puddle of water big enough for a frog butt, and this was normal-- even in a San Francisco subdivision. There is a new quiet normal and I feel sad for anyone too young to have experienced the bounty of my youth. In this article I have attempted to read and synthesize the latest scientific literature concerning the relationship between honeybee decline and the use of systemic neonicotinoid pesticides.
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| Apis mellifera S.Reeve |
I have looked at the issue of disappearing honeybees for years. I read everything I see concerning this issue. It is not just honeybees that are dying, pollinators have declined precipitously in the last twenty years. Monarch butterflies in the U.S. numbered one billion in the 90s and are now around 33 million, a decrease of 90% (Xerces Society). Native bumblebee populations have fallen. Several, once common species, are now rare or presumed extinct (Xerces Society) (1). Population decline has affected at least one fifth of U.S. bumblebee species, with some species close to extinction, and their ranges have shrunk (2). According to Sydney Cameron, an Entomologist at University of Illinois, Urbana-Champaign, “There are whole regions where we can’t find them anymore.” There are many reasons for the alarming decline of pollinators: loss of habitat, introduced disease, climate change, and pesticide use (Xerces Society).
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| Figure 1 Western Monarch Count 1997-2009 Xerces Society |
Honeybees are also dying. Since 2006, the USDA estimates that 10 million honey bee hives have failed. Many scientists blame neonicotinoids for the disappearance of nearly a quarter of the honeybee colonies over the winter of 2013 in a phenomenon termed “Colony Collapse Disorder” or CCD. Neonicotinoids are a class of systemic pesticides, and the most widely used insecticdes in the world (3). Colony Collapse Disorder began to be a problem in 2004 when neonicotinoids started to become widely used as a prophylactic seed treatment for corn (Figure2). Currently, corn is planted on 84 million acres and constitutes the largest crop in the US (EPA). Since 2004, nearly all major agricultural crops receive neonicotinoid seed treatments increasing treated acreage to approximately 275 million acres. This is a lot of chemical when you consider that every single corn kernel planted has a coating of 1.25 milligrams of neonicotinoid pesticide which has the potential to kill over 100,000 bees (3). Corn kernels are also coated with numerous fungicides too (13).
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| Figure 2 Dr. Susan Kegley Pesticide Research Inst. |
And while neonicotinoids are especially toxic to arthropods, they kill birds too. Cynthia Palmer, co-authored a report that found a tiny grain of coated wheat can kill a songbird (6) An especially troubling aspect of widespread seed treatment found no crop increase as a result, and insignificant benefit according to a recent scientific literature review (3). In total,140 different crops are treated with neonicotinoids, and hundreds of millions of acres of agricultural lands, gardens, golf courses , parks, homes, and lawns are treated with neonicotinoids every year. Frequently used flea and tick treatments for pets also contain these pesticides. Neonicotinoids are a class of systemic insecticides with high toxicity to insects through neurotoxicity(3,5,7,13,15). They work by preferentially binding to nicotinoic acetylcholine receptors in the nervous system of insects and cause stimulation, receptor blockage, paralysis, and death. When the neonicotinoid binds the receptors never close and are thought to be irreversibly harmed leading to excitation and eventually to death of the receptor, and when enough receptors are harmed --death of the bee.
The effects are cumulative, and bees are exposed in multiple ways throughout the growing season, from seed treatment dust, to pollen and nectar, and through accumulation in the hive (2,3,5,8). Remember, too, that crops are treated with multiple pesticides, fungicides, and herbicides which are collected in the hive (11,12). An nationwide analysis of 887 hive waxes and pollens found 121 different pesticides (12). Almost 60% had a neonicotinoid, occurring at up to 99 ppm (with sublethal effects at 5-10 ppb) (12). Close to 50% of the samples had multiple pesticides, acaricides, herbicides, or fungicides (11,12). Toxic load of multiple pesticides have additive and synergistically negative effects on honey bee health (10, 11). So it is no mystery why bees and other organisms are dying, in fact, it is almost a wonder that ANY exist with this chemical onslaught.
Neonicotinoids have sublethal effects at remarkably small doses of ≥0.5ng/bee (clothianidin) and ≥1.5ng/bee (imidacloprid) (3,5,7). Multiple exposures of 20+ppb cause death, and one dose of approximately 142ppb is the acute lethal toxicity (15). To put it another way, a bee weighs 1/10th of a gram and the median lethal dose or LD 50 of Clothiandin, a neonicotinoid, is only 3 billionths of a gram (13,14). Compared to DDT, Imidacloprid, a neonicotinoid, is 10,000 times more toxic (3). If you wanted to kill honeybees, Clothiandin is what you would use. It is one of the most toxic chemical formulations for honeybees in existence(13).
Neonicotinoids have sublethal effects at remarkably small doses of ≥0.5ng/bee (clothianidin) and ≥1.5ng/bee (imidacloprid) (3,5,7). Multiple exposures of 20+ppb cause death, and one dose of approximately 142ppb is the acute lethal toxicity (15). To put it another way, a bee weighs 1/10th of a gram and the median lethal dose or LD 50 of Clothiandin, a neonicotinoid, is only 3 billionths of a gram (13,14). Compared to DDT, Imidacloprid, a neonicotinoid, is 10,000 times more toxic (3). If you wanted to kill honeybees, Clothiandin is what you would use. It is one of the most toxic chemical formulations for honeybees in existence(13).
Multiple exposures from environmental sources and hive-stored pesticides increase behavioral problems in bees (3,5,7,13). In tiny doses, neonicotinoids disturb bee navigation and memory, slow foraging behavior, and compromise social interactions, and communication (5,7,8,10). Reduced fecundity, and depressed immune systems are also implicated in neonicotinoid use (9). Increasing the dosage keeps bees from finding their way back to the hive which results in the characteristic symptom of CCD which is the absence of adult bees in the hive, and live brood and queen still present . There are currently 150 products approved for home and garden use that contain neonicotinoids, and over 465 products registered (Washington State Extension).
Neonicotinoids are systemic pesticides, that are water-soluble, and persistent in the environment (3,4,13,14). Because they are water soluble and systemic, they are readily taken up by plants through the vascular system (3). Soil or foliage treatments are both successful at spreading the pesticide throughout the plant, and become accessible to bees and other pollinators through nectar, pollen and guttation drops (13, 15). One study, by Penn State Entomologist, Dr. David Biddinger, found measurable amounts of residues in woody plants up to six years after application (15). He also found that chemical residues left in the soil from a previous year can be absorbed by untreated plants (15). Neonicotinoids contaminate surface water, ground water, and soil, endangering not only pollinators, but also other beneficial species that inhabit these ecosystems (4). Mayfly nymphs, for example, the bottom of the aquatic food chain and an important food source for many organisms, are killed at only one part per billion of neonicotinoids (3). One study of 136 wetlands, found as many as 91% had measurable levels of neonicotinoids, with a mean concentration of 91.7ng/L, and a high 3110ng/L or three times the level required to kill mayfly nymphs (4). Combine this with the fact that these chemicals bioaccumulate in environmental systems and have a half-life of up to three years it is easy to see the environmental damage they are causing (3, 13,15). Over 90 percent of neonicotinoids turn up in water and soil affecting large numbers of target and nontarget organisms, and creating widespread environmental injury (3,4,).
Sales of neonicotinoids are a multi-billion dollar business with profits reaching 2.6 billion dollars a year (3). Pesticide companies are interested in maintaining this income stream and use many tactics to direct the attention away from neonicotinoids.
http://ecowatch.com/2014/04/28/pr-tricks-pesticide-companies/
Tactics include: diverting attention away from neonics, blaming farmers and beekeepers, manufacturing doubt, targeting children, and spinning science. This works. Even with all of the environmental damage the United States has failed to take any regulatory measures against the use of neonicotinoids. Changes are being made on the local level, as Eugene, OR has become the first city to outlaw their use. We can only hope for the sake of affected organisms on land, in the air, and in the water, that many other communities will follow suit.
References:
1) Cameron, S.A., J.D. Lozior, J.P. Strange, J.B. Koch, N. Cordes, L.F. Solter, and T.L. Griswold. 2011. Patterns of widespread decline in North American bumble bees. Proceedings of the National Academy of Sciences 108:662-667.
2) Williams, N., 2003. Plight of the bumblebee. Current Biology 13, R463.
3) Goulson, D. (2013) An overview of the environmental risks posed by neonicotinoid insecticides. Journal of Applied Ecology, 50, 977–987.
4) Main AR, Headley JV, Peru KM, Michel NL, Cessna AJ, Morrisey CA (2014) Widespread use and frequent detection of neonicotinoid insecticides in wetlands of Canada’s Prairie Pothole Region. PLoS ONE 9:e92821
5) Yang,E.C.,Y.C.Chuang,Y.L.Chen,andL.H.Chang. 2008.Abnormal foraging behavior induced by sublethal dosage of imidacloprid in the honey bee (Hymenoptera: Apidae). J. Econ. Entomol. 101: 1743Ð1748.
6) Mineau, P., Palmer, C. 2013. The impact of the nation’s most widely used insecticides on birds.
7) Schneider, C. W.; Tautz, J.; Grünewald, B.; Fuchs, S. RFID tracking of sublethal effects of two neonicotinoid insecticides on the foraging behavior of Apis mellifera. PLoS ONE 2012, 7, e30023.
8) Henry, M., Beguin, M., Requier, F., Rollin, O., Odoux, J.-F., Aupinel, P. et al. (2012) A common pesticide decreases foraging success and survival in honeybees. Science, 336, 350–351.
9) Gill, R.J., Ramos-Rodriguez, O. & Raine, N.E. (2012) Combined pesticide exposure severely affects individual and colony-level traits in bees. Nature, 491, 105–119. doi: 10.1038/nature11585.
10) Wu, J.Y.; Anelli, C.M.; Sheppard, W.S. Sub-Lethal effects of pesticides residues in brood comb on worker honey bee (Apis mellifera) development and longevity. PLoS One 2011, 6, e14720.
11) Johnson R.M., Ellis M.D., Mullin C.A., Frazier M. (2010) Pesticides and honey bee toxicity – U.S.A., Apidologie 41, 312–331.
12) Mullin, C. A., M. Frazier, J. L. Frazier, S. Ashcraft, R. Simonds,D.vanEngelsdorp,andJ.S.Pettis. 2010. Highlevels of miticides and agrochemicals in North American apiaries: implications for honey bee health. PloS ONE 5: e9754.
13) Krupke, C.H., Hunt, G.J., Eitzer, B.D., Andino, G. & Given, K. (2012) Multiple routes of pesticide exposure for honey bees living near agricultural fields. PLoS One, 7, e29268.
14) EPA (United States Environmental Protection Agency). 2003 Pesticide Fact Sheet: Clothianidin.
15) Hopwood J, Vaughan M, Shepherd M, Biddinger D, Mader E, Hoffman Black S, Mazzacano C (2012) Are neonicotinoids killing bees? http://www.xerces.org/neonicotinoids-and-bees/. Accessed June 2014
