A recent study from Purdue University entomologists raises serious questions about seed treatments. The bulk of the study refers to bee deaths reported at planting time in 2010 and 2011 where neonicotinoid insecticides were present in the dead bees. However, information gathered for the study may have even broader ramifications.
To beekeepers, the findings were significant enough. Among the findings was that a high concentration of neonicotinoid was found in talc (added for flowability) left behind in planters. The compound (below levels considered toxic to bees) was also found in corn pollen brought to the hive mid season, as well as in dandelion pollen at corn planting time. The researchers also reported bees at the hives exhibited "tremors, uncoordinated movement and convulsions, all signs of insecticide poisoning."
With U.S. beekeepers reportedly losing a third of their hives each year, finding the cause or causes has become a holy grail for many. Honeybees are the main pollinators of American agriculture, contributing an estimated $15 to $20 billion annually in many key crops. While some beekeepers have been quick to blame crop protectants for 'colony collapse,' no smoking gun has yet been found.
Jack Boyne, entomologist and director communications, Bayer, is confident the neonicotinoids are not it. "We have 34 studies conducted on clothianidin showing no harm to honey bees," said Boyne. "They include a study where bees were fed up to 100 ppb of the compound with no immediate adverse affects."
Greg Hunt, Purdue professor of behavioral genetics and a honeybee specialist and co-author of the study, acknowledged there is no one apparent factor to blame for colony collapse. At the same time, he pointed to a growing view among bee researchers that a combination of mites, insecticides and other factors may be to blame.
Other findings in the study may have even broader implications. Neonicotinoids were found in the soil throughout the fields sampled... as long as two years after application, though they may last longer. To entomologists, such persistence in the soil, combined with near total market penetration by neonicotinoid products, may be creating ideal conditions for resistance development.
Dave Fisher, director, environmental toxicity and risk assessment, Bayer, argued that as it ages, the product is tied up in the soil and very little is taken up by following crops. Boyne added that limiting application to the individual seed in the row allows sufficient refugia between the rows.
While Christian Krupke, Purdue associate professor of entomology and another co-author of the study, is unaware of studies regarding soil particle binding of the compound, he contested the refugia argument.
"If every single crop/seed is treated (the case with corn), then you have maximum pressure for insects that feed on corn to develop resistance," said Krupke. "If the dose is lethal, the choice is to adapt (develop resistance) or die. If the dose is sublethal but has negative effects, adaptation will also occur. What is in the surrounding soil is irrelevant."
Although Krupke acknowledged the potential for resistance, he emphasized the impact on honeybees and other pollinators has more urgency behind it. In both cases, however, the persistence and widespread use makes evaluation difficult.
"We have a neonicotinoid landscape today," said Krupke. "Where can you find an area that honeybees won't come into contact with any of these toxins? How much is too much, and where are the lethal and sublethal thresholds of these materials? Does 3 ppb do anything to honey bees or other beneficial insects?"
What Krupke does know is that the compounds don't stay in the row or the plant. "It has potential to go wherever water flows and dust blows," he said. "The premise that these insecticides stay in the corn field is false."
What is also clear is that research with bees is difficult at best. Fisher described that difficulty with controlled conditions, such as tent or tunnel studies. "The problem is you can only keep the colony healthy for a couple of weeks," he said.
Going to the field can be equally problematic. A controversial EPA ordered and approved study conducted in 2007, though requested years earlier, purported to show the safety of clothianidin to bees. Hives were placed in six Alberta Ontario canola plots (four treated/two untreated), each with a canola field. An area of 2 1/2 acres around the hives was treated. Although Bayer defends the rigor of the study, pointing out minimal other bee-attractive plantings in the area, critics point out that bees will forage for miles, far beyond such a small area, even though canola predominated in pollen brought to the hives during the study. With the continued expanded use of neonicotinoids, a similar study today might be questioned because it is virtually impossible to find an untreated control, given the widespread product use.
What is certain is that more study is needed. An internal November 2010 EPA memo regarding expansion of the clothianidin label to cotton and mustard recommended multiple new studies, including bee impact. A recently released study out of Italy suggested bee deaths can result simply from bees flying through fields where air planters operate.
In addition to studies on bees and other beneficial insects, Krupke suggested more studies are needed simply to better evaluate when and if seed treatments are even needed. Boyne reported an average return of 6 to 14 bushels per acre. While the Purdue entomologist acknowledged a value exists, he also questioned the need to treat every single seed.
"Baseline studies on the many, many pest and non-pest insects that encounter this material are lacking," he said. "We don't have a good understanding of what these products are contributing to yield and stand establishment. Seed treatments may be hugely beneficial if conditions are right, but we don't know when they are needed. Placing them on each seed, every year runs contrary to the fundamental principles of insect pest management. We know from past experience that ignoring those principles is asking for problems.”