Poplar trees are a very good source of propolis, This being a resin is a
very good sink for most pesticides

Quote
"Beekeepers in parts of MN are having pesticide kill problems that appear to
be due to spraying hybrid poplar plantations.  Much insecticide is used on
these trees and much damage is being done to the beekeepers in the area.
These losses have been going on for about 4 - 5 years but it has taken the
beekeepers that long to figure out what seems to be going on."
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