Corn Seed Treatment As Lethal As It Gets For Honey Bees All Season Long, And Long After The Season Is Gone. It Just Keeps On Killing.
by Alan Harman
Frightening new research shows honey bees are being exposed to deadly neonicotinoid insecticides and several other agricultural pesticides throughout their foraging period. The research, published in the scientific journal PLoS One says extremely high levels of clothianidin and thiamethoxam were found in planter exhaust material produced during the planting of treated maize seed. The work, which could raise new questions about the long-term survival of the honey bee, was conducted by Christian H. Krupke of the Department of Entomology at Purdue University, Brian D. Eitzer of the Department of Analytical Chemistry at the Connecticut Agricultural Experiment Station and Krispn Given of Purdue.
“Neonicotinoids were found in the soil of each field we sampled, including unplanted fields,” they report. Dandelions visited by foraging bees growing near these fields were found to contain neonicotinoids as well. “This indicates deposition of neonicotinoids on the flowers, uptake by the root system, or both. Dead bees collected near hive entrances during the spring sampling period were found to contain clothianidin as well.”
“These results have implications for a wide range of large-scale annual cropping systems that utilize neonicotinoid seed treatments,” the report says. The research was funded by grants from the North American Pollinator Protection Campaign and the Managed Pollinator Coordinated Agricultural Project.
Neonicotinoids are persistent. The new report says the half-lives of these compounds in aerobic soil conditions can vary widely, but are best measured in months – 148 – 1,155 days for clothianidin.
Among the largest single uses of these compounds is application to maize seed. Production of maize for food, feed and ethanol production represents the largest single use of arable land in North America, reaching a record
88,216,620 acres in 2010 and is expected to increase. All of the maize seed planted in North America except for 0.2% used in organic production is coated with neonicotinoid insecticides.
Two major compounds are used – clothianidin and thiamethoxam, with the latter metabolized to clothianidin in the insect. The application rates for these compounds range from 0.25 to 1.25 mg/kernel. These compounds are highly toxic to honey bees – a single kernel contains several orders of magnitude of active ingredient more than the published LD50 values for honey bees – defined as the amount of material that will kill 50% of exposed individuals.
In fact, the amount of clothianidin on a single maize seed at the rate of 0.5 mg/kernel contains enough active ingredient to kill more than 80,000 honey bees.
The results prompted researchers to carry out more experiments to determine how honey bees may be gaining exposure to clothianidin and other pesticides commonly applied to either maize seed or to plants later in the season. They collected samples from a variety of potential exposure routes near agricultural fields and analyzed them to determine whether pesticides were present. They sampled soils, pollen both collected by honey bees and directly from plants, dandelion flowers, and dead and healthy bees. They even checked waste products produced during the planting of treated seed. Maize seed is sewn with tractor-drawn planters that use a forced air/vacuum system and a perforated disc to pick up individual seeds and drop them into the planting furrow at the selected spacing. Maize kernels treated with neonicotinoids and other compounds such as fungicides do not flow readily and may stick to one another, causing uneven plant spacing. To overcome this, talc (a mineral composed of hydrated magnesium silicate) is added to seed boxes to reduce friction and stickiness and ensure the smooth flow of seed. Much of the talc is exhausted during planting, either down with the seed or behind the planter and into the air using an exhaust fan. Researchers sampled the waste talc after planting to determine whether this material was contaminated with pesticides abraded from treated seeds. The waste is a mixture of the talc that has been in contact with treated maize kernels and minute pieces of the seeds.
To read the study, click here:
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