Sounds like a nasty pest! And being a flying pest as an adult chances are they will spread rapidly. Seems to me like most of the more damaging pests we have in the US have been imported.

That really sucks... only 200 miles from me. I hope my alliums will be ok next year. By the time you see the symptoms to row cover it is probably too late. Plus on onions the row covers increase heat and decrease light... not great.