Hi Jack It looks like your question was not answered yet, so let me see if I can help. The worm that is eating your iris bulb is most likely the iris borer which is a pinkish caterpillar. Dig up the irises and cut away the infested parts and then replant. In fall, clean up all the debris around your iris as this can be an overwintering site for this pest.
In spring, eggs may be laid on the new foliage, so be looking for damage. When the leaves are about 5 or 6 inches tall they can be sprayed with acephate to control the new generation. Check with you local Extension office to see if the product is recommended in your state.