It looks like bean beetles.  There are Mexocan Bean Beetles that can defoliate your beans. 

You can hand pick early in the AM and later, near dusk when they are less active. You can also try insecticidal soap, as well as Spinosad, Neem or pyrethrum.  There is a beneficial insect you can buy from places like Arbico.  It is Pediobius favedatus.  Be sure to scrape off the egg masses which like a explosion of yellow.  The adults look alot like ladybugs. In the future try spacing your plants out to 4-6" as well as try planting earlier and.or later in the season when they are not yet hatched (or already have disappeared).

Good luck. They are a big problem for a lot of us.

Cecily, Master Gardener Volunteer