Acanthoscelides obtectus- A seed saver’s lament

Homegrown Neighbor here:

Well, I had a rude awakening when I tried to plant my beans a few weeks ago. I have been growing several different types of pole beans for three or four years and saving seeds from them at the end of every summer. I usually grow purple, yellow and green varieties of pole beans for beautiful summer soups, salads and other dishes.

Not this year. When I opened the packet of bean seeds that I had saved last fall, I found all of these little holes in my beans. Turns out the culprit is the bean weevil, Acanthoscelides obtectus.

Their larvae make swiss cheese out of dried beans.

While they can be a pest in the garden apparently they usually are a problem in stored beans. And it turns out they love our mild California winters which allow them to reproduce year round. I also looked them up on the handy dandy University of California Integrated Pest Management site. Turns out not having dried beans around is the best way to control them. I probably am storing too many seeds in my garage. This fall I’m going to use glass jars instead of paper envelopes and see if that keeps some of the critters out.

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  1. I was going to say refrigerator, that’s where I keep all my seeds. and while the seeds are in paper, they are then in another container too

  2. Wow! I’ve never seen holes in dried beans before. They almost look like tiny ocarinas.

    Bummer. Thanks for the IPM link- I’m hoping they do better for me than my IPM book, which so far hasn’t really been very helpful.

  3. Would borax hurt the seeds? We use that as a dessicant to kill fleas in our carpet/furniture, so it might help with the beetles.
    Also, I find that paper or plastic are poor defense against critters (bug or mammal). Food quality glass or air-tight shutting metal tins are my storage venues of choice.

  4. I suspect you’ll find that the eggs were present on the beans when you stored them, so enclosing in glass won’t help. If you’re opposed to using an insecticide, placing seeds in a Ziplock bag and putting that the freezer will be your best defense.

  5. I’ve read that, if the eggs are present at the time of packing for storage, you can leave them in the freezer for just a week or so to kill them and then store them elsewhere. Though, now that I think about it, the drastic change in temperature might be a problem…

  6. Glass won’t help – if the beans have been exposed to the critters (ex in the drying process) you will have critters inside the glass jar (voice of experience).
    I would hesitate to use the borax that annonymous said, because I wouldn’t want to be putting borax into my garden soil (when I plant the beans) — I think if you look it up you’ll find it would be toxic to your soil micro-life. Try the short-term freezing that megan/mason suggested. I believe Susanne Ashworth recommends that as well. Also check all other paper-stored beans that were nearby the beans that got eaten.

  7. Short term freezing works very well for pantry moths and weevils, too. If you have some suspect flour or grain, freeze it for 4 days. It makes sense it would work for seed.

    I’ve also heard that with particularly persistent infestation, intermittent freezing–that is, setting up a freeze/thaw cycle to trick the bugs–works well.

  8. Would carbon dioxide work? I have heard of using “dry ice” but mixing baking soda and vinegar also produces CO2 (+ water) and CO2 is heavy so you might be able come up with a gizmo to get it into the jars. My daughter did this for a science fair experiment with growing plants in a high CO2 atmosphere and we tested for the presence of the gas by extinguishing a flame in the bottom of a jar.

  9. Also, try Diatomaceous Earth. It works on grain, so it ought to work on beans.


  10. Diatomaceous earth will work only on adult insects. The larvae, which do the actual damage, don’t have a waxy cuticle or even an exoskeleton to be covered by a cuticle, so DE is just dust to them.

    Fenugreek hay (yes, I realize that is redundant…sorry), on the other hand, is toxic to them, and not to soil microbes or humans. I say plant a few fenugreek seeds now, make hay every once in a while, and crush up the dry leaves at the end of the season as sort of an insecticidal packing material around any seeds you save.

  11. As several other people have noted above, the beans almost certainly contained weevil eggs when you put them into storage. This is always a problem for me, but happily the solution is simple: freezing.

    Put the beans into a sealed container, and keep them in the freezer for 5 to 7 days. After that they can come out of the freezer again, and they’ll be fine, since the freezing kills the eggs. Just be sure the beans are completely dried out when you freeze them, though, otherwise you’ll kill the beans, too. (Doesn’t matter if you’re aiming to eat them, but if they’re for seed…)

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