Answer: It sounds as though you're dealing with an infestation of Mexican bean beetles. Adults are round beetles with 16 black spots on their wings, and can be mistaken for orange colored ladybugs. They can be formidable foes. Inspect plants frequently; handpick adult beetles from the plants and squish their yellow-orange eggs (found on the undersides of leaves). You may be able to manage the pest population at acceptable level simply by interplanting beans with garlic, nasturtiums, marigolds, or potatoes, which help repel the beetles.
Be sure to clean up bean plant debris right after harvest so adults won't have a place to hide. Plant beans early to avoid attack, and try growing a variety of plants to attract predacious wasps and assassin bugs, both of which eat Mexican bean beetles. Since beans are self-pollinating, you can cover the plants with fabric row cover to create a barrier agains the beetles.
As a last resort, spray plants weekly with an organic pesticide such as neem. Make sure to spray the undersides of leaves as well.
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