rose-barndance-c-jap-beatles1There are few things more frustrating or discouraging than working hard to create something beautiful and then having to watch it made ugly and be destroyed. Anybody who gardens has probably had this experience due to deer, rabbits, voles, moles, molds, Japanese Beetles or other pests. Knowing your enemy is empowering so I have been researching Japanese Beetles, my current nemesis, and here are some interesting facts about their life cycle that help to understand and control them.

The Ten Facts

1. Adults emerge from the soil on warm sunny days beginning in late June and continuing through July. They warm themselves and then begin to feed as soon as possible. Although they eat over 400 plant species they prefer only about 50.

2. Feeding adults release a congregation pheromone with attracts other adults as they emerge later so that masses of adults gather on some unfortunate victim plant.

3. As females emerge they release an additional sex pheromone that attracts males. Mating may take place on turf with several males waiting for the opportunity with the newly emerged female.

jap-beetles-stacked4. Mating may also occur while feeding. I have seen three and four beetles stacked up in a mating position and wonder who is mating with whom and how do they figure it out.

5. After feeding for a couple of days the females stop feeding in the afternoon and burrow into the soil to a depth of 2-4” and lay 1-5 eggs in the soil.

6. Females repeat this feeding, mating, laying routine every 1-2 days.

7. Under warm, moist conditions the eggs hatch in about 2 weeks and develop into grubs that feed on the roots of plants such as grass.

8. Grubs burrow deep into the soil as temperatures fall and return to the top layer in spring when temperatures rise.

9. Grubs form pupae in early June.

10. The pupae form adults by mid to late June and the cycle is complete.

Possible Control Methods

There are insecticides that are effective but since they also hurt bees, butterflies, earthworms, and other wildlife directly or indirectly I choose not to spray.
Traps are discouraged by most authorities because they will attract the beetles from all over your neighborhood into your garden. Once there they will be attracted by the pheromones to the plants where your own beetles are feeding and mating. If you want to buy a trap, buy one for your neighbor.
Biological methods of control involve bacteria and nematodes and are not considered very effective.
Keeping the lawn and garden soil dry to impede the development of the eggs and grubs is a possibility but may hurt the lawn and garden more than it hurts the beetles. If it rains your efforts will be useless and you will loose this years plants no matter what.
Picking the beetles off our plants by hand is the best alternative and for the past three years has worked. We sustain some damage to both flowers and leaves but nothing so bad that the plants will not recover. We have to put in about 30-40 minutes/day the first week but the process is very easy and the time spent collecting goes down .

Our Plan of Attack

jap-beetle-catcher1 The head gardener (a.k.a my husband) cut a gallon milk jug into a collection container (see picture). It has a handle and a large opening so we can shake a fairly large leaf or branch into the opening. We put a couple of inches of water and a few squirts of dish detergent into the jug.
We start our collection between 10:00 and 12:00 in the morning after the sun has warmed the soil and leaves of plants. All we do is shake the branch, flower or leaf on which we see beetles and they drop right into the jug and drown. This is not the prime collection time but we want to decrease the feeding damage.
We do another collection between 2:00 to 4:00 PM when we know that we will find a lot of beetles feeding and mating. By this time the pheromones are causing large clusters of beetles to congregate on relative few flowers and leaves. We don’t want the fertilized females to get a chance to lay eggs.
We do a final collection about 7 PM and see many beetles still feeding and mating.

We start the process as soon as we see the first Japanese beetle in June and continue until we see no more beetles. Most of the problem is in the rose garden where the beetles congregate on certain roses (mostly yellow ones) and ignore others. A few beetles can be found on some of the plants in the formal garden about 100 feet away. I feel sure that our roses are attracting beetles from the formal garden as well as all over the neighborhood but even so we are able to get control over them in a couple of weeks.

I am sure there are other methods for controlling these pests and if you think about their lifecycle you might come up with a fantastic plan that suits your garden and circumstances better than our method. Understanding the enemy is power!

Garden Pest Pointer

By Karen

23 thoughts on “Ten Interesting Facts About Japanese Beetles as an Aid to Control”
  1. The beetles in our yard seem to prefer the area under the bird feeder. The ground is soft and moist. Scrub Jays, attracted to the seed, are finding the buried beetles.

  2. Is there anything that Japanese beetles will not eat? If so, that is what I am going to plant to replace my fruit trees that they have killed despite using milky spore, collecting them in jugs, and using powder killers on them. Not only do they eat the plants, they fly at me and attack if I come near them. My roses are gone, my wisteria, my japanese maple, all my fruit trees – everything –

    1. Janice,Where is your garden? Sounds like you have a horrific problem. Depending on where you live, there are plants that they ignore, like conifers. Of course, when the food supply is low animals will eat things they never would have under better conditions, so I suppose Japanese beetles could be the same way. Perhaps you should look into killing the grubs while they are developing in the soil.


  3. Karen,
    Thank you for posting the “10 interesting facts”. This is the second year we have been bothered with Japanese Beetles. They are quickly destroying our knockout roses. Today I sprayed an insecticide called Neem Oil that can be used in organic gardening. I’ve seen claims that it is effective on J.B’s. Have you ever heard / tried it?

    1. Jan,
      Yes, I have heard of it and have heard that it is very good and environmental friendly. No,I have not tried it. I usually pick the Japanese Beetles off my roses, sometimes a very arduous task but usually easier than getitng out all the gear to spray.

      Good luck with your “Knock Outs”.


  4. Karen,
    I’ve had quite an infestation this year of Japanese Beetles & have been picking them off by hand into soapy water – a few hundred per day. They’re all over my wonderful raspberries, sunflowers & grapevines. They haven’t touched my roses, tho. Maybe it’s because I’ve treated the roses with a systemic food & insecticide from Bayer.
    I’m worried about next year with the grubs attacking my lawn. I may try the milky spore.
    Eric Engelson

    1. Eric,
      Sorry to hear of your Japanese beetle problems but you are lucky they didn’t go to your roses too. You’re right about the potential grub problem but consider that for each one of those Japanese beetles you capture each day you have significantly lessened the number of next year adults. I usually fine a bad year is followed by a good year but have no data on this. Good luck with the milky spore.


  5. Karen,
    I recently moved into a home with beautiful gardens in front and back yard.
    Not only do I think the gardens are beautiful, but so do the Japanese beetles!
    They are eating the knockout roses, crepe mrytle regularly and almost everything else for dessert. I’m also noticing that a Butterfly Weed and Coneflower next to each other are not doing well. Branches are dying individually and wondered if the grubs could be responsible?

    I had a beetle bag which I got rid of after reading your ten tips and have been catching beetles daily in the dish soap and water mixture. My neighbor used the Bayer systemic product early in the season and has no beetle problems at all. She has knockout roses as well as Japanese maples. I’m still learning the names of everything the former owner planted and don’t have as much time as she did to plant, etc. but I certainly don’t want to loose anything due to my lack of knowledge.

    1. Jennifer,
      I am sorry to hear about your Japanese beetle problem and I know how you feel watching them gobble up the roses and crepe myrtle. Your neighbor is using a very good product but do you know what it is killing in the soil besides the beetle grubs? I don’t and it worries me so I try to hold off on using chemicals. There comes a point, of course, when it is either the chemicals or the plants so I understand why people turn to the chemicals and I do too at times. By the way, spraying with Sevin helps with the Japanese beetles and is safer than many other chemicals.


  6. Japanese Beetles- After I was able to identify these buggers, I found Karen’s website and found a lot of helpful tips about eliminating these critters. But, I found 3 of them in my living room. Two of them were on the screens and the other one was perched on a pillow. These are the first that I have seen this year and I don’t remember seeing them last year. I might not have paid as much attention if they were outside, but definitely paid attention when seeing them in the house. At first, I thought they were pretty cool, as they looked like scarabs. Then found out they are in the scarab family and lastly, found out what pests they are. Any ideas as to why they came in the house, when the plants are all outside? Thanks, Martha

    1. Martha,
      Here are my best thoughts, none being great. 1) They came in on some flowers you picked for the vase, like roses; they could easily bury into roses and you would never know until they emerged. 2) Someone brought them in on clothing, shoes etc. They generally want no part of humans so I find it hard to believe that they would get on someone let alone be transported by anyone. 3) They were attracted by some houseplant inside 4) They aren’t actually Jap. beetles.

      Sorry I have no better suggestions. I have never heard of Jap beetles coming indoors but, of course, there is no reason why they couldn’t.

  7. I’ve found 3 Jap beetles in my house. the first one fell out of the folds of my morning newspaper.Could my dog be responsible for the other two? The 3rd one was in the upstairs hallway!

    Every day, I find more and more gray leaf skeletons underneath my linden. I’m going to have to start raking them up! I’ve never seen such an infestation.

    1. Virgina,
      Too bad about your Japanese beetle problem. Some years it is bad others not so bad. Perhaps next year you will not see any. I suppose your dog could bring them in but so could you on flowers, clothing or shoes. Drop them into soapy water and they will perish. Good luck.


  8. Karen,
    One of my co-workers says that she has been drowning the Japanese beetles she collects in her rain barrel, then scoops them out to dispose of them once they’re dead. Does this contaminate her rain water in any way? She only uses it for watering her garden.

    1. Marilyn,
      If dumping Japanese beeteles in the rain barrel works I see no reason not to do it. On the other hand, I find that the Japanese beetles can escape plain water and that is why I put detergent into my collecting container. The detergent seems to interfere with their escape and they ultimate die in the container. Also, decaying Japanese beetles are very smelly so if any are not scooped out that would be a negative for me.


  9. Karen,
    Is it possible that the Japanese Beetles are attracted by T1-11 siding? I have a problem in my yard and have noticed that the beetles are worse by the building made of this material. I spoke to someone else who has a building made of this material and the beetles are worse by his building. I know someone else who lives in my area that doesn’t have a beetle problem and she doesn’t have any building made of this material on her property.

    1. Linda,
      Anything is possible with these pests but I have never heard that any siding attracted them. However, the problem may have something to do with rain runoff from the roof or side of the house making the area along the building more hospitable to beetle larvae. There are insecticides that can kill the grubs but they kill good things too so I have never used them. I pick beetles off my infected plants and dump them into cans of soapy water where they die. They are a terrible pest but seem to be a bigger problem some years than others so I just hope for the best and keep picking.

  10. Karen,
    This past summer I sprayed my knock-out roses with Sevin in mid-June before the jb’s began their usual annual smorgasbord. I then sprayed after each time it rained. We ended up with only a few diners.
    I plan to plant 2 Kwanzen Cherry trees this fall. Are they part of the “50” preferred species? Is the list of “50” published somewhere?
    Also, what and when do you recommend for jb grub control?

  11. Be careful of these “innocent” insects! I had just seen a few of them on my roses and about 3 days later, was in a separate part of my yard and I felt one hit me directly on the ear while it was in flight. In a split second,it was burrowing down my ear canal and pushed past my attempt to close off my ear from the outside. It proceeded to chew on my ear canal and inside. It was the worst pain I have ever been in and a flashlight to draw it out only made it more agitated. After pushing against it in my ear, it stopped moving. 2 doctors,2 doctor’s offices and about an hour later, they painfully were able to get it out. Worst experience ever!!!!!!!!! I would never try to shake them off the plant. TRUE STORY!!!!!!!!!

    1. Holly, You experience sounds horrible. Sorry to hear that they could be so dangerous. Glad to hear that you are well enough now to tell about it.


  12. I was picking off japenese beetles yesterday, and there was a HUGE one about 1 inch long, 3/4 inch wide. Is this considered a queen?

    1. Joyce,
      Not that I know of. You probably got a different kind of beetle that looks similar to a Japenese beetle but larger.


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