We are back with a new edition of our series on the common tree diseases and insect pests in the Chicago area as we discuss a group of pests that causes problems throughout the U.S.; bark beetles.  There are around 6,000 species of bark beetles worldwide under the subfamily Scolytinae and there are 600 that are found in the U.S. and Canada.  Many invasive species of bark beetles have been found in the U.S. and in some areas, like California,...