The beans (pole beans) that I save to plant the following year always end up with multiple holes from bugs by the time spring rolls around. The beans still sprout and grow fine, but I'd rather not have the bugs. I gather up quite a few beans at the end of the season and stash them in an envelope in the garage over the winter (mild calif. temperatures). No pests are visible when I put away the seeds in the fall, so I guess the eggs are hiding in the beans from the beginning.
From the internet, it seems that they might be "weevils". Many internet sites on how to save seeds, but I haven't seen one that tells how to stop bean bugs. Have found advice to put seeds (in general) in freezer to kill pests, but they also mention beans in specific may be harmed or killed by freezing unless extremely dry. (Dry enough to "shatter": I don't think mine ever get that dry).
Any tips how to get my seed beans clean & bug free? Just to be clear, I am not trying to get rid of any kind of infestation in the garden while it is growing. I just don't like the aesthetics of opening my seed envelope in the spring and finding the beans riddled with holes and a thick layer of insect droppings, powdered bean dust & maybe dead bugs at the bottom. Even though the beans do germinate and produce just fine, and I don't see the bugs alive in the garden during the summer.