Streets of Portland carpeted with dead bumblebees as 5th mass mortality strikes the city this month

[Emily]

[h=1]Cause unknown in spate of Portland bee die-offs[/h] By Kelly House | The Oregonian/OregonLive Corinne Fletcher stepped outside her apartment building Friday morning to find a pollinator genocide in the park that serves as her backyard.
Dead and dying bumblebees littered the sidewalk near the Market Street entrance to downtown Portland's Pettygrove Park. The carcasses were so thick, the Lewis & Clark College law student said, "you had to step carefully to not step on any bees."
The fifth mass bee death in Portland in the past several days has state investigators on the hunt for a cause.
...
"We're trying to find out whether this is something humans did to the bees ? a pesticide or pollutant or something ? or is there something weird going on with the trees?" Odenthal said...

http://www.oregonlive.com/environment/index.ssf/2015/06/cause_unknown_in_spate_of_port.html

These recent events were associated with the same species of urban ornamental trees that are sprayed with insecticides to control nuisance insects and were related to previous mass bee deaths in another OR city:

https://flutrackers.com/forum/forum...eaths-in-hillsboro-safari-pesticide-suspected

But OR was reported to have banned the used of suspected pesticides on Linden trees in March:
http://www.beyondpesticides.org/dai...our-bee-killing-insecticides-on-linden-trees/

There is a species of Linden with some natural toxicity to bees:
http://www.ext.nodak.edu/extnews/hortiscope/tree/linden.htm