Pesticide causes largest mass bumblebee death on record

Toll climbs to 50,000, affected 300 wild colonies

Tens of thousands of bumblebees and other pollinators were found dead under trees at the Target store in Wilsonville on Saturday. The discovery was a strange and ironic start to National Pollinator Week, a symbolic annual event intended to raise public awareness about the plight of bees.

The massive bee kill was documented on Monday by Rich Hatfield, a conservation biologist with the Portland-based Xerces Society for Invertebrate Conservation. Several shoppers at the store called him to report that there were dead and dying bees all over the parking lot. Specifically, the bees were clustered under dozens of European linden trees. The Xerces Society is internationally known for its work on bee conservation.

After several calls at the office I visited the Target store in Wilsonville and found a parking lot full of dead bumblebees underneath blooming European linden trees, said Hatfield. They were literally falling out of the trees. To our knowledge this is one of the largest documented bumblebee deaths in the Western U.S. It was heartbreaking to watch.

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.

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.

I visited the site (June 19), and saw bees on the ground in the process of dying. Its a very unfortunate situation. Hopefully, (Oregon Department of Agriculture) can provide some information, Rappold said.

The Xerces Society contacted the Oregon Department of Agriculture, which responded by sending staff to collect samples of the bees and foliage from the trees. According to staff members at the agriculture department, they determined the trees were treated with an insecticide by Safari called dinotefuran.

It seems a landscape company did not follow label directions as it is not supposed to be sprayed during bloom, said Scott Hoffman Black, executive director at the Xerces Society. We now assume this is the cause of the massive bee die-off. Lots of bees still dying  almost all bumblebees.

We are very happy with the quick action by ODA to get to the site and collect bees for testing, said Mace Vaughan, pollinator conservation program director for the Xerces Society.

Hatfield estimated there were at least 25,000 dead bumblebees, a number that likely represents the loss of more than 150 colonies. There were also dead honeybees, lady bird beetles and other beneficial insects. Bumblebees are especially important to agriculture in western Oregon, where they are considered vital pollinators of many berry crops and Willamette Valley seed crops.

We think that the initial kill was either cleaned up or the bees were eaten by birds so it is hard to get an overall number. To be on the safe side we are still estimating over 25,000, which would be the largest known kill of bumblebees, Black said.

We need to spotlight this as a real-world lesson in the harm these toxic chemicals are causing to beneficial insects, Black said. It would be especially alarming to find out whether pesticides are the cause in this case because the linden trees are not even an agricultural crop. Any spraying that happened would have been done for purely cosmetic reasons.

According to Mark Ottenad, city public and 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.

The ODA may send out a crew to trim off all of the flowers, which is a huge job on 55 individual 30-foot-tall trees with flowers on all branches, said Black.

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.