Investigators have discovered 30 unauthorized commercial honeybee hives near the site of a large bee die-off in Sherwood southwest of Portland.
Observers reported thousands of dead honeybees on a busy stretch of Highway 99W on Sunday.
The die-off triggered concern in part because of a mysterious phenomenon known as colony collapse disorder that wipes out honeybee colonies. It also follows a massive bee die-off in a Portland-area Target parking lot last year that was caused by an ill-timed pesticide application.
The Oregon Department of Agriculture is investigating. Agency spokesman Bruce Pokarney said this time of year it's common for swarms of honeybees to leave their hives. He said officials now suspect the bee die-off may have been caused by traffic hitting a swarm of bees from the nearby hives.
"We're trying to figure out who owns those hives," Pokarney said. "It appears the bees in question did come from those hives."
Pokarney said investigators haven't found evidence that pesticides played a role in the die-off. They're now planning to test the bees in the hives for signs of illness.
The hives were found on property owned by the City of Sherwood, but the city hadn't approved them.