Cathy
Your photo is of nymphs (young) of the southern green stink bug. The nymphs of this true bug go thru quite a few colorful changes before becoming a solid green adult bug.
This group of stink bugs feed on plants of all kinds. They are considered a pest of tomatoes, beans, berries, peas and others in the garden and in the ag fields on soybeans and cotton to name a few. The mouth parts are piercing/sucking so if they pierce a spot on fruit early in it's development it can deform the fruit to be unmarketable. Piercing new shoots deform them also.
Organic control consists of keeping the area free of weeds, esp noted in one UCDavis study mallow, mustards, thistles. and mullein. They suggest a trap crop of alyssum will attract the bugs then you can collect or spray the bugs there to prevent them from getting on the garden. Also, you can spray with insecticidal soap. You might check the label of Spinosad to see if it is labeled in Calif for stink bug control. It is a bacteria that affects some insects.
Here are photos of the nymphal stages and the adults.
http://bugguide.net/node/view/19047/bgimage
