The Recurring Silent Spring
November 20, 2014
Honeybee colony collapse disorder (CCD) threatens the survival of honey bees, and consequently the ability of many plants to reproduce. As such, it affects food production and agriculture. CCD is not occurring only in the United States. It is also happening in Europe and other parts of the world, leading to a growing sense of global alarm, as at least one-third of the world’s food production depends on honeybee pollination.
When it first emerged in 2006, CCD was considered a mysterious and symptomatic disease because of its unusual and unique post-mortem observations. Honeybee colonies that died of CCD were previously considered healthy; however, over a short period of time, adult bees disappeared from or abandoned their hives during winter, when bees normally would stay inside their hives. Hives struck by CCD were left with very few dead bees but with abundant stored honey and pollen.
Suspect: Sub-lethal doses levels of neonicotinoid insecticides
One suspect in this epidemic is a relatively new class of insecticides called neonicotinoids. Neonicotinoids affect the central nervous system of insects, resulting in paralysis and death. Studies conducted in the late 1990s suggest that neonicotinic residues can accumulate in pollen and nectar of treated plants and represent a risk to pollinators.
Although neonicotinoids are known to be acutely lethal to bees, it is evident from studies I have conducted that CCD is caused by neonicotinoids’ unknown sub-lethal toxicity. None of the bees in our studies died acutely during the 13-week of neonicotinoids administration; instead, honeybee colonies collapsed over multiple brood generations that coincided with winter season.
In my most recent study I collaborated with the Worcester County Beekeepers Association to study the health of 18 bee colonies in three locations in central Massachusetts. At each location, we separated six colonies into three groups—one treated with low doses of imidacloprid, one with low doses of clothianidin (both are neonicotinoids), and one untreated. There was a steady decline in the size of all the bee colonies through the beginning of winter—typical among hives during the colder months in New England. Beginning in January, bee populations in the control colonies began to increase as expected, but populations in the neonicotinoid-treated hives continued to decline. By April, six out of 12 of the neonicotinoid-treated colonies were lost, with the abandoned hives that are typical of CCD. Only one of the control colonies was lost—thousands of dead bees were found inside the hive, with what appeared to be symptoms of a common intestinal parasite called Nosema ceranae.
While bees in this study, which was published in the Bulletin of Insectology, experienced a 50 percent CCD mortality rate among the pesticide-treated hives, a previous study we conducted with low doses of imidacloprid showed bees in pesticide-treated hives having a much higher CCD mortality rate—94 percent.
While it is true that the survival of honeybees could be affected by a set of stressors and pathogens, those factors already existed prior to the emergence of CCD and could not explain the unique characteristics associated with CCD hives, namely the abandonment of hives in winter. Moreover, if CCD were caused by weakening immunity first due to pathogen infestation, and then induced by neonicotinoids toxicity, the CCD hive would be left with thousands of dead bees.
Lethal to birds, too
The detrimental effect of neonicotinoids is not confined to honeybees. According to a report released by the American Bird Conservancy (ABC) in March 2013, wild birds in the U.S. are affected as well. The ABC report, titled “The Impact of the Nation’s Most Widely Used Insecticides on Birds,” concluded that neonicotinoids are lethal to birds and to the aquatic systems on which they depend. A single seed coated with a neonicotinoid can kill a songbird. Even a tiny grain of wheat or canola treated with imidacloprid can fatally poison a bird. And ingesting as little as one-tenth of a coated corn seed per day during egg-laying season is all that is needed to affect reproduction. The ABC report also concluded that neonicotinoid contamination levels in both surface and ground water in the United States and around the world are already beyond the threshold found to kill many aquatic invertebrates. This conclusion was supported by a 2014 study published by the U.S. Geological Services.
Research into the sub-lethal toxicity of neonicotinoids, although not required by EPA during product registration, is most relevant to CCD as neonicotinoids may pose a high risk to pollinators and wild birds. Since the neonicotinoids are systemic insecticides – infiltrating the entire plant including the pollen and nectar -- their spread cannot be contained or prevented. No matter how neonicotinoids are used, via seed treatment, soil drench, tree injection, or foliar application, they will be absorbed, trans-located, and spread within and beyond the crops. With much longer half-lives than other insecticides, neonicotinoids have become ubiquitous and persist in the environment, accumulating in plants, soils, and water systems. Considering neonicotinoids’ extended half-lives and the systemic property, it appears there is no safe level.
Neonicotinoids are considered to be less toxic to mammals. This may not hold, as recent studies have shown their detrimental effects to the development and functioning of our brains and the peripheral nervous system. The inhibition of nicotinic acetylcholine receptors (nAChR) in insects in which neonicotinoids targeted may operate universally to most organisms, including humans. The lack of toxicological studies in animal models and epidemiological research in human populations has rendered a false sense of safety of neonicotinoids in species other than insects.
Learning the lesson of Silent Spring
Rachel Carson would not be foreign to this scene if she were to stand in front of the hives that died of CCD on an early spring morning. In her book “Silent Spring,” Ms. Carson attributed the decline of bird population in the U.S. to the excessive use of organochlorine insecticides, namely DDT, in the 1960s. An analogy exists to the occurrence of CCD in 2014. It is a shame that we are failing to learn from the lessons documented in “Silent Spring.” Instead of taking positive and precautionary steps at an early stage to intervene in the deteriorating health of pollinators, birds, and other invertebrates, USDA/EPA has decided to muddy the waters by focusing on multi-factorial causes that dilute the significance of neonicotinoids. The recent presidential memorandum to create a federal strategy to promote the health of honeybees and other pollinators, although a baby step in the right direction, does not address the principle of the problem because it makes no mention of reviewing neonicotinoids’ sub-lethal toxicity to bees and other organisms.
The prompt determination of eliminating DDT from our food chain successfully removed America’s bald eagles from the endangered species list. We could claim the same victory on behalf of bees and other organisms by ridding our environment of neonicotinoids. Honeybees may not possess the majestic and political symbol of bald eagles, but they play an essential, vital, and irreplaceable role in feeding the human population and keeping ecological systems humming.