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Pesticide causes largest mass bumblebee death on record

Toll climbs to 50,000, affected 300 wild colonies


by: LORI HALL - Crews of three to four used boom lifts to drape large pieces of netting over the trees.Scientists investigating the mass death of bumblebees in Wilsonville say that pesticides are the cause. The incident first came to light June 15 when shoppers at Target 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 its international bee conservation work, which 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 bumblebees ever documented, and thankfully ODA is taking the issue very seriously.”

Lake Oswego resident Cassandra Platz said she noticed the bees Saturday when she was shopping around noon. She had parked near one of the trees and noticed the bees.by: LORI HALL - Rich Hatfield and Ashley Minnerath, of Xerces Society, staple together large pieces of netting to cover the trees. Behind them is a tree already covered.

“All the trees had dead and dying insects,” Platz said. “I parked by one of the trees and there were just masses of them. I was just disturbed.”

According to Kerry Rappold, Wilsonville natural resources program manager, the 50 to 55 affected European linden trees are on Target property.

Large-scale deaths of domestic honeybees 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,” Vaughan said. “The fact that this happened in an urban area is probably the only reason it came to our attention.”

After interviewing the landscaping company, whose name has not yet been released by the ODA, 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 more than 50,000 bumblebees 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,” he said.

ODA has confirmed that the bee deaths are directly related to the pesticide application on the linden trees, which was conducted June 15.

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, scientists are now concerned about whether the trees will still be toxic next year when they flower again.

According to Vaughan, because the trees were sprayed rather than being fed, or the ground saturated with the pesticide, the trees should not be poisonous for more than a few months. However, bees are only attracted to the flowers, which should die off in two to three weeks and the trees will no longer be a draw for the insects.

A large conference call was conducted June 19 between the city, Xerces, ODA and other entities to try to prevent further bee deaths. Options included cutting down the trees, removing all the flowers manually, trimming branches or using more chemicals to combat the pesticide — none of which seemed like good options.

According to Mark Ottenad, city public/government affairs director, “The city has not, so far as I am aware of, ever had any situation like this. We are, nonetheless, very concerned. ... The city is adjacent to some of the most productive agricultural land in the state and bee pollination is essential to the agricultural industry.”

In the end, they came up with the idea of enclosing the trees in a mesh fabric to keep the bees off the trees until the flowers die, according to Wilsonville Planning Director Chris Neamtzu.

The large pieces of netting were allocated from Oregon Bag Company in Canby and were then stapled together to create swathes large enough to cover the tall trees. The material is a shade cloth commonly used to protect tender plants in a greenhouse.

On Friday, crews from ODA, Xerces and the city of Wilsonville worked all day to cover each and every tree, a process that took 30 to 45 minutes per tree.

Vaughan gave kudos to Wilsonville for stepping up and stepping in on the problem.

“The city was in a position to take a lead. We’re prepared to respond to emergencies. We felt like we had to jump into action,” Neamtzu said.by:  LORI HALL - Crews worked all day Friday to cover the blooming trees with large nets to keep bees and other polluniators off the poisonous flowers.

The city was also ready to bear the burden of the costs associated with the materials and labor of covering the trees, however, Safari has offered to defray costs by cutting a check.

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,” Black said.

Investigators learned of the poisoning 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.

“To my knowledge, there has never been a documented bumblebee kill to this scale,” Vaughan said. “This is unprecedented. ... Bumblebees, for Oregon, are the most important wild pollinator we have. Bumblebees are the most important pollinator period.”

Vaughan warned that bumblebees are always being killed on a smaller scale when people use pesticides on the ornamental trees, bushes and plants in their yards.

“Bumblebees are very important pollinators of many agricultural crops. Especially important crops in Oregon like blueberries and raspberries. Although it will be difficult to tell how this one incident impacts agriculture, we believe this is a real reason to educate people about the adverse impacts that pesticides can have on these important animals,” Black said. “In most cases, pesticides are really not needed at all in urban/suburban areas. In this case there was no economic benefit that we know of from using them. If you do not need pesticides do not use them. If you do need to use them do the background reading to understand how they might impact pollinators as well as other important animals.” 

ODA is continuing its investigation of the incident to determine if the pesticide application was in violation of state and federal pesticide regulations.




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