Yahoo! News has this report about the discovery of the cottony psyllid (Psyllopsis discrepans) in North Dakota. The psyllid is native to Europe but likely entered North Dakota via Canada, where it has been chewing up ash trees for several years.
Update: Cottony psyllid may not be as new to the US (or Canada) as the above article implies. Specimen of the insect have been collected in St. Paul, Minnesota in 1993, in Michigan in 1955, and in Nova Scotia way back in 1921. Looks like more investigative work needs to be done before we get the big picture about the origin of the North Dakotan invasion and the extent of the cottony psyllid's spread.
Thanks to the Systematic Entomology Laboratory for providing this information.