Pesticide Causes Largest Mass Bumble Bee Death on Record

Photo: Motoya Nakamura/The Oregonian

Photo: Motoya Nakamura/The Oregonian

Oregon Department of Agriculture confirms deaths due to application of insecticide known as Safari. Read the details here.

Wilsonville OR. — Scientists investigating the mass death of bumble bees in Wilsonville, Oregon say that pesticides are the most likely cause. The incident first came to light on Saturday when shoppers at a Target store reported finding tens of thousands of dead bees in the store’s parking lot. News quickly spread to the Portland-based Xerces Society for Invertebrate Conservation, a group known for their international bee conservation work, who launched an investigation.

“We immediately contacted the Oregon Department of Agriculture (ODA) and asked them to test the bees for pesticide poisoning,” said Mace Vaughan, the Xerces Society’s Pollinator Conservation Director. “To our knowledge, this incident is the largest mass poisoning of bumble bees ever documented, and thankfully ODA is taking the issue very seriously.”

Large-scale deaths of domestic honey bees have been reported in recent years, but among wild pollinators, documented poisoning incidents of this scale are largely unprecedented, according to experts. “Wild bees are killed all the time in agricultural fields where nobody sees it happen,” said Vaughan. “The fact that this happened in an urban area is probably the only reason it came to our attention.”

After interviewing the landscaping company that maintains dozens of ornamental trees around the Target parking lot, ODA investigators learned that the pesticide Dinotefuran had recently been applied. Investigators confirmed that Dinotefuran, sold under the trade name ‘Safari,’ belongs to a class of insecticides called neonicotinoids that have been linked to bee deaths in recent years.

Rich Hatfield, a biologist with the Xerces Society, estimates that over 50,000 bumble bees were killed, likely representing more than 300 wild colonies. “Each of those colonies could have produced multiple new queens that would have gone on to establish new colonies next year. This makes the event particularly catastrophic.”

ODA has confirmed that the bee deaths are directly related to a pesticide application on the linden trees conducted last Saturday, June 15 to control aphids. The pesticide product Safari was used in that application. Safari, with its active ingredient dinotefuran, is part of a group of insecticides known as neonicotinoids. According to investigators, the insecticide was originally applied to control aphids, which secrete a sticky residue while feeding, and can be a nuisance to parked cars. Dinotefuran and other neonicotinoids are a relatively new group of insecticides that are long-lasting in plant tissues. Because of this, the scientists are now concerned about whether the trees will still be toxic next year when they flower again. Emergency measures to prevent further bee deaths were taken today by staff from the ODA, Xerces, and the City of Wilsonville. By the end of the day all of the trees will be covered with large nets to prevent bumble bees and other pollinators from reaching the flowers.

Scott Black, executive director of the Xerces Society, noted that the pesticide was applied to the tree while it was flowering, an action that violates the product’s instructions. “Beyond the fact that a pesticide was applied to plants while they were attracting large numbers of bees, in this case the pesticide was applied for purely cosmetic reasons. There was no threat to human health or the protection of farm crops that even factored into this decision.”

Investigators learned of the poisoning—the largest of it’s kind ever recorded—on the first day of National Pollinator Week, an annual symbolic event that is intended to raise awareness about the plight of bees, and their role in the environment.

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