Polyphylla decemlineata

The ten-lined june beetle (Polyphylla decemlineata) is one of the most attractive pests in the Western US. It emerges towards the end of June / early July here in Fresno at which time it begins showing up at porch lights.

It's the unseen larvae (feeding as grubs on roots) that cause the damage, and they are known to feed on a variety of plants. In a suburban neighborhood (were I live) it isn't really possible to know who's yard they are coming from and so controlling them can be a challenge. If you have unhealthy grass (or grassy areas) you might want to treat it. The adults aren't a problem and birds love to eat them, and keep their numbers down for the most part. In rural areas they can be a problem in peak years.