I was walking the McArthur Island Golf Course with Jesse Ritcey and Rick Tucker today. In various places, we noticed some well-marked, roundish beetles on deer-browsed shrubs and cottonwood saplings. Some beetles were singles while others were mating.
I took some photos which allowed me to identify them as Cottonwood Leaf Beetles (Chrysomela confluens.) A Google search found a few brief notes about them. The colour pattern in my photo is one of two forms, the other being dark, iridescent purple-brown. As you can see, the pronotum is black with reddish margins – very distinctive in this form. The beetles eat the leaves of willow and poplar.
When disturbed, they exude a salicylaldehyde-based secretion which is effective against generalist predators. It has a bitter almond odour.

The second photo shows a mating pair, or nearly so.