PORTLAND, Ore. (Reuters) - Hundreds of bumblebees have been found dead in downtown Portland during the past two weeks, prompting agriculture officials in Oregon to investigate whether the die-offs may be connected to other bee deaths reported across the country over recent years.
Bumblebees and their cousins, the honey bee, have been dying off at alarming rates. In particular, honey bees, which are critical agents in the pollination of important U.S. crops, disappeared at a staggering rate over the last year when losses of managed bee colonies topped 42 percent year-on-year in April. Scientists, consumer groups and beekeepers have pinned much of the blame on pesticide use.
But the bees found dead in Oregon this month may have been reacting to a natural agent, said Dale Mitchell, pesticide program manager with the Oregon Department of Agriculture.
“In all four incidents, bees were found near one species of tree,” Mitchell said. “We have no indication that pesticides were used on the linden trees where they were found, but there has been some research suggesting that the bumblebee is not able to process the nectar in these trees.”
The linden tree originated in Europe, and North American bumblebees may not be able to handle a chemical that occurs naturally in its nectar, a hypothesis researchers at Oregon State University are exploring, Mitchell said.
He would not rule out the possibility that pesticides may also have played a role in the recent Portland deaths.
In 2013, more than 50,000 bees dropped dead at an Oregon Target store whose parking lot was filled with lindens that had been treated with insecticides, prompting state officials to restrict use of the neonicotinoid class of pesticides, which has been identified as a major source of bee colony collapses elsewhere in the world.
Since those restrictions went into effect, fewer massive-scale bee die-offs have been reported in the state, Mitchell said.
Editing by Cynthia Johnston and Ken Wills