Japanese Beetles in Prairies – How Much Should We Worry?

Japanese beetles (Popillia japonica) first appeared in the U.S. back in 1916 (in New Jersey) and have been spreading west since then.  They’ve only started to be abundant in our part of Nebraska during the last several years.  As a result, I’m not really sure what to expect in terms of potential impacts to our prairies.  I’m largely writing this post to hear what my friends to the east have been seeing, since the little buggers have been around there longer.

Japanese beetles are known pests of gardens and crops, but what are their impacts in prairies?  This one was eating the flowers from leadplant (Amorpha canescens)

While I’m not sure what to expect in prairies, our family has had plenty of experience with their ability to damage our garden crops.  Japanese beetles wiped out our raspberry crop last year and were trying really hard to kill our little apple tree this year.  I’m not a fan.

For those of you not familiar with Japanese beetles, they are about 1/2 inch long beetles that are metallic green with brown wing covers.  The series of white spots around the edge of their abdomen are actually little patches of white hairs, and those help distinguish them from lots of other metallic green beetles.  The larvae feed mostly on the roots of grasses, and they are a big pest in lawns and other turfgrass situations.  As adults they’re known to attack over 300 different plant species, with corn, soybeans, maples, elms, plums, roses, raspberries and grapes among their favorites.  Hence, they are pretty unpopular with gardeners and farmers alike.

Adults emerge in the early summer and seem to spend the vast majority of their time eating and mating – often at the same time.  Females take breaks from feeding/mating to burrow a few inches into the soil in grassy areas and deposit a few eggs.  Then they come back out and join the crowd again for a while.  They can repeat their burrowing/egg laying up to 16 times a season.  Most adults live for about a month or month-and-a-half, but some can live up to 100 days or more.  They are skeletonizers of plants, meaning that they feed on the portions of leaves between the veins, leaving behind only the skeletons of those leaves.

Japanese beetles skeletonizing leaves of Illinois tickclover (Desmodium illinoense)

I’ve been trying to pay attention to Japanese beetles in prairies, but I don’t feel like I’m learning very much yet.  The biggest infestations I’ve seen have been in the small prairies here in Aurora (Lincoln Creek Prairie).  In bigger prairies outside of town, I don’t see nearly as many.  At Lincoln Creek, the beetles feed on a lot of different plants, but seem to have special attraction to tick clovers (Desmodium) and the flowers of roundheaded bushclover (Lespedeza capitata).  However, while I’ve seen many plants nearly covered with beetles, many others manage to successfully bloom and make seed, so I don’t yet see the beetles having any major impacts.

Japanese beetles  feeding and mating on roundheaded bushclover (Lespedeza capitata)
Despite a heavy presence on Illinois tickclover flowers and leaves, many plants still produced seed this season, at least at Lincoln Creek Prairie in Aurora, Nebraska

Help?  What are those of you in the Midwest and further east seeing in prairies that have had decades or more of Japanese beetle infestations?  Any evidence that they might wipe out particular plant species?  Should we be concerned about them in our Nebraska prairies or just focus on protecting our gardens and crop fields?

Any advice is welcome – thank you.

22 thoughts on “Japanese Beetles in Prairies – How Much Should We Worry?

  1. Nancy Cusumano August 21, 2018 / 12:13 pm

    If you can use them in your prairie, Japanese beetle traps work very well, and one trap covers a lot of area. Possible on your thousands of acres though?

    • michaelwatsonvt August 21, 2018 / 1:53 pm

      Traps have the unfortunate side effect of drawing beetles from afar. Hand picking seems more effective when it is feasible. We noticed a sharp decline in their numbers when we stopped using traps on a friend’s recommendation.

  2. Stephen Packard August 21, 2018 / 12:33 pm

    In my experience they’re creepy in their over-abundance. But they don’t seem to attack our rarer plants. They don’t seem to kill anything. Especially abundant on hazel, grape, Desmodium, and Napaea.

    Might they weaken some species over the long run? Hard to guess. Perhaps some disease or predator will find and adapt to them and bring them low (or “into balance” as we used to say).

  3. Robert J. Fleming August 21, 2018 / 12:59 pm

    Yes, tons of them on tick clover, just south of Des Moines. Like you, not sure of impact.

  4. Ellen Rathbone August 21, 2018 / 1:29 pm

    In NYS we had a fungus being used as biological control. I started seeing JBs with white dots on their backs – sometimes one, sometimes two. I made a few calls, and voila – it was an effort to control the burgeoning population! No idea how it stands today – I’ve not been there for 8 years.

  5. John Blakeman August 21, 2018 / 1:38 pm

    I’ve frequently encountered Japanese beetles in the Northern Ohio prairies I’ve created, studied, and managed since the 1970s.

    I’ve discerned no particular prairie plant species preferences of the beetles, but surely they exist. The problems have been so minimal that the bugs have warranted no detailed study in Ohio prairies — thankfully.

  6. michaelwatsonvt August 21, 2018 / 1:50 pm

    Here in Vermont their populations seems somewhat cyclical. The last few years we have seen very few, this after several years of rapidly increasing populations. Their overall impact appears to be limited to minimal.

  7. Mary Brong August 21, 2018 / 2:40 pm

    I cannot speak to your question about prairies but for your raspberry plants and apple, use a little hand-held vacuum and suck them up. Freeze them over night and put the dead beetles out for the birds. Within a few years you won’t many Japanese beetles left. The traps attract them and make the problem worse, in my experience.

    • A. Vazquez August 21, 2018 / 8:34 pm

      What a great idea – thank you for sharing this! I am using Milky spore, but it takes a year or two to be effective. Your idea will help with the immediate crisis without hurting our pollinators!

  8. jimluyten August 21, 2018 / 4:20 pm

    Hi, Chris – love your posts! We lived on Cape Cod for ~46 years and used milky spore to suppress the larvae. I recommended this to the mgmt at MidTown Crossing and I believe they used it – this year has been much more manageable even though elsewhere it’s been a brutal year for them in Omaha…

  9. Jan Curry August 21, 2018 / 6:41 pm

    We had a large outbreak of them this year in the Kansas City area. I found them on many natives. They seemed especially fond of common and purple milkweed flowers, and partridge pea. I seem to have developing seeds, but not sure if they will be viable, or of their usual number. They also worked on my pawpaws, but seemed to only damage the foliage.

  10. James McGee August 21, 2018 / 9:29 pm

    I’ve seen them in prairies, but I’ve never really paid much attention to what they were eating. They particularly like rose mallow, Hibiscus moscheutos (palustris), in my garden. The plant they seem to like more than anything is Virginia creeper, Parthenocissus quinquefoilia. I would suggest planting some Virginia creeper in the vicinity of your garden to keep them from eating other plants. I mostly eliminated them from my yard by flicking the ones on my Virginia creeper into a cup of soapy water over the course of a few years. Once the population was eliminated it never rebounded. The only downside is my Virginia creeper is now growing over everything and I have to cut it back frequently.

    I do have one gripe I attribute to them. I purchased a $50 white lady’s-slipper orchid (Cypripedium candidum) grown from tissue cultured seed by Great Lakes Orchids. After I planted this orchid in my garden it did great.


    The next year it never emerged. When I dug it up to see what happened all I found was a grub and the ends of the roots that had not yet been eaten. I don’t know how to identify grubs, but since Japanese beetles cause problems in lawns it seem likely this species was responsible.

  11. cpowersbrady August 21, 2018 / 9:48 pm

    I remember Jap. beetles being new pests on raspberries in the early 1960’s in NE Ohio, if that provides any timeline for their spread west. They are cyclical. In suburban environments, well-watered lawns are ideal for JP grubs. Rose family seems especially appealing to adults, but damage seems seasonal. Can’t speak to prairie impact, but haven’t noticed any locally (Chicago suburbs).

  12. Rodger Benson August 22, 2018 / 8:02 am

    I saw them wearing out a Rough Pigweed plant last summer but have been attentive to them this year and have not seen much.

  13. Weeds Henry August 22, 2018 / 11:03 am

    One of their favorite food plants here in a 10 acre prairie has been Gaura biennis and that seems to have declined greatly in numbers, though not eliminated.

  14. Laurie Lovell August 22, 2018 / 3:45 pm

    They’ve done a number on native plums and commercial rose family fruit crops. This is central Missouri. Some of them are after the oak leaves and they really love locust (black). Lots of treetop damages. The Burr Oak Co-Champion in the McBaine Bottoms
    has a lot of tip damage from them.

  15. Carol Meteyer August 23, 2018 / 7:24 am

    Just a caution to avoid mistaking our native dogbane beetle (*Chrysochus auratus*) for the Japanese beetle [image: image.png]

    On Tue, Aug 21, 2018 at 1:09 PM The Prairie Ecologist wrote:

    > Chris Helzer posted: “Japanese beetles (Popillia japonica) first appeared > in the U.S. back in 1916 (in New Jersey) and have been spreading west since > then. They’ve only started to be abundant in our part of Nebraska over the > last several years. As a result, I’m not really su” >

  16. Susan Kleiman August 23, 2018 / 10:38 am

    Agree with all comments on prairie plants I’ve noticed them on, but would also include Evening Primroses. Also not sure if any permanent damage.

  17. Karen H. August 23, 2018 / 3:33 pm

    I have witnessed cicada killer wasps stinging and carrying them away on two separate occasions. Unfortunately, my neighbor hates these wasps and kills them on sight. Perhaps he will feel differently when the beetles eat his garden.

    • Jim Worth August 26, 2018 / 5:57 am

      Interesting! Thanks for that info!!!

  18. brucemohn September 9, 2018 / 7:15 am

    I saw swarms of them at my parents’ property in Lebanon County, PA. Saw some feeding in their vegetable garden, but the largest swarms were on their roses. I tried collecting them by hand, but wasn’t entirely successful. The beetles tended to drop and then fly off as soon as they detected me. I wondered if this was typical beetle behavior or if it perhaps was the clue to their success, since it seems that they are just as palatable to insect eaters as the native species.

  19. Kathy Olson September 18, 2018 / 3:17 pm

    I liked the trap the first time I tried that several years ago in N. Illinois. It filled up and then a raccoon ate them all. I also saw some on Japanese Knotweed too. I was not sorry at the time to see the knotweed being eaten by Japanese beetles. Overall it seems we have less this year. I could be wrong. I’m hoping that the nature is now starting to balance out. Our current infestation is now stink bugs. Before it was beer bugs and Japanese ladybugs. Now not so much.


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