This is a native leaf beetle (Calligrapha californica, tickseed leaf beetle per ODA ID) which feeds on Asteraceae, such as bidens, boneset, coreopsis, dahlia, goldenrod, marigold, and ragweed.

http://oregonstate.edu/dept/nurspest/Calligrapha%20californica%20clup4.html

Christine Buhl
May 15, 2017, 12:44 a.m.

As I am sure you are aware some insects are cyclical depending on availability of food sources and conditions. Further there are over an estimated 60,000 species of insects (that we know of) in Oregon! Meaning that sometimes we don't see some until we start looking for them (e.g., you don't realize how many other people drive Jeeps until you buy one). It was likely just a good year for these little guys, but not to worry this little uptick in numbers should not be an issue.

Christine Buhl
June 8, 2017, 6:40 a.m.