Iridescent Beetles eating our plants
We have hundreds of small, iridescent beetles eating our grape leaves. We have never seen them before and don't know where they came from and what to do to about them. We live in North Denver.
Denver County Colorado japanese beetles
Those are Japanese Beetles, a pest that has become a big problem in the Denver area only recently. They eat the foliage and flowers of over 300 different species and grapes is one of their favorites. They won't kill it, but they will skeletonize the foliage.
They can be difficult to control. We recommend hand-picking and dropping them into a container of soapy water as the first line of defense so as not to do harm to pollinators that are also present. That may be impossible on your grape if it is large, so you could consider spraying it with a neem oil product that contains the ingredient azadirachtin but you will have to repeat the spray every 3-4 days. Here's a fact sheet with more information: http://extension.colostate.edu/topic-areas/insects/japanese-beetle-5-601/
The good news is that we are approaching the end of their season. The adults have been busy laying eggs in lawns where they overwinter and new adults will reemerge next June and start the cycle over again.