I looked up this beetle when I got home from our nature journal meetup. Turns out, this is one of the most widely distributed eucalyptus leaf beetles in Australia, but it was only discovered in the US (here in Los Angeles) a year ago.

Paropsis atomaria is considered a pest in eucalyptus plantations in Australia and is reported to cause defoliation, decreased growth and wood quality, and sometimes tree death. Both larvae and adults feed on the foliage. Development from egg to adult takes approximately one month and there are up to four generations per year

So this cute little beetle is quite the eucalyptus scourge. I bet there are many California native plant supporters who are not unhappy that it has reached our shores — eucalyptus species themselves being invasive around here.