Meet The Beetles: Frederick Dobbs on Japanese Beetles

In my yard, it’s no longer possible to grow cherries to harvest because the flowers and nascent fruit are devoured by Japanese beetles (Popillia japonica). Roses too, a favored food, are decimated.

I had never seen a Japanese beetle before 10 years ago. That was when they first arrived in my area. But the beetle has been in North America since at least 1916, when it was found at a nursery at Riverton, NJ, not far from the W. Atlee Burpee Company. It is thought to have entered the country several years earlier as eggs on a shipment of iris tubers.

As with many exotic (nonnative) species, and particularly invasive ones, Japanese beetle has few natural enemies here, and presented with a favorable climate and an abundant food supply, it has thrived and has become established. It is now a serious plant pest and a threat to lawns, gardens and agriculture in general.

Japanese beetle is usually spread to new locations as eggs or grubs in soil surrounding nursery plants. Adult Japanese beetles are often found around airports, presumably transported by cargo planes. Since its introduction, despite quarantines, Japanese beetle has spread to most, if not all, states east of the Mississippi River and into parts of Minnesota, Iowa, Missouri, Nebraska, Kansas, Arkansas and Oklahoma. There are two known pockets of infestation in Colorado, one near Denver and the other in Palisade area on the West Slope, suggesting that the Rocky Mountains are not an insurmountable barrier. Studies predict that Japanese beetle will become established in all states bordering the Gulf of Mexico.

There are a number of control strategies that can reduce beetle populations and feeding, and there is lots of information available on the internet (see for example the following USDA site: and through county agricultural agents and garden shops. Most control recommendations rely on long-term, multifaceted approaches focusing on combinations of chemical, cultural, and biological practices. There is no simple (and effective) one-shot approach.

More knowledge is better than less, and any control strategy should be based on the dynamics of the beetle’s life cycle. In the Northeast in June, adults emerge from the soil, where they have overwintered as grubs. They then feed, mate, and lay eggs until a killing frost. The peak of adult beetle numbers is July and August. Eggs are laid in the soil after a few weeks of feeding and mating. A female can lay 40 to 60 eggs during her life. Eggs hatch in July and the resulting grubs feed on the roots of grasses, sometimes causing dead patches in a lawn. Grubs are fully grown by the end of August. Older grubs are quite tolerant to drought and high moisture.

When the soil cools to about 60°F in the fall, grubs move deeper underground, and most overwinter at 2 to 6 inches below the surface. When soil temperature rises above 50°F in the spring, grubs begin to move up into the root zone, feed for 4 to 6 weeks, and undergo pupation (the transformation from grub to adult). Adults emerge and the cycle repeats itself.

There are a number of synthetic insecticides that target different points in the beetle’s life cycle. There are also “biorational” insecticides derived from plants or other natural sources that have modes of action different from conventional insecticides; these are considered to have lower risks to humans, wildlife, and the environment. Conventional and biorational insecticides have a place in a control strategy. Consult local county agricultural agents and garden stores for recommendations.

Among the cultural practices that are utilized to reduce beetle populations are habitat manipulation and trapping. Japanese beetle feeds on almost 300 plant species, but it will feed on some plants only moderately or not at all. The composition of plants in a lot or garden can thus have a significant influence on the attractiveness of a property to Japanese beetles. This may be cold comfort to those in highly infested areas with mature landscaping, but beetle plant preference should be considered when replacing woody plants and in what herbaceous ones are grown. See Tables 1 and 2.

Traps are commonly sold in hardware stores and garden shops. They are baited with beetle pheromone or floral scent. They are remarkably effective in attracting beetles. Observing the beetles at traps, it’s easy to see that the beetles are not very good flyers. Beetles bounce off the sides of the trap, overshoot it, or simply congregate on its side, mating, sunning, or clambering over each other. For every four beetles that a trap attracts, only three are captured. My belief is that a trap attracts more beetles to a property than had one not been used; the net effect is more beetle damage. Traps should never be placed near plants that beetles favor.

In its native habitat in Asia, Japanese beetle is not as destructive as it is here. A long-term control strategy that makes good sense is determining and promoting Japanese beetle parasites and pathogens. USDA has introduced several exotic insect parasites of Japanese beetle. These have shown varying degrees of success. There are also nematodes and bacterial pathogens that are effective in checking beetle populations and that are relatively easy for gardeners and homeowners to use.

USDA entomologists imported (1920s and early 1930s) an Asian wasp called spring tiphia (Tiphia vernalis) that is parasitic to Japanese beetle. These wasps attack beetle grubs. In the spring after mating, the female burrows into the soil looking for grubs. When she finds one, she attaches an egg to it. The egg hatches and the larva feeds on and eventually kills the grub. The wasp larva overwinters in the soil in a cocoon from which it emerges in spring to start the cycle over. Spring tiphia were released in Connecticut between 1936 and 1949. Recent surveys show that the wasp is present in every Connecticut county and is attacking Japanese beetle grubs.

Another parasitic insect imported from Asia by USDA is Istocheta aldrichi, a tachinid fly. In North America, tachinid flies are an important group of insect parasites. In Asia, Istocheta aldrichi specifically parasitizes adult Japanese beetles. The fly attaches its eggs to the thorax of the beetle, and the larva hatches within 24 hours, bores into the beetle, and begins to feed.

This fly was introduced to New England at about the same time (1922) as spring tiphia. It is established in much of New England and is found on 20% or more of Japanese beetles tested. In Japan, I. aldrichi is the primary biological control agent for Japanese beetle, but in New England, it is not well synchronized with the beetle’s life cycle and tends to emerge earlier than the beetle. In more northern areas (Maine, for example), where I. aldrichi emerge later, synchronization appears to be better. The fly may thus be a good candidate for introduction in the North Central states.

Active research is continuing with both of these insects, and efforts are being made to establish the fly in new areas. To my knowledge, there are no commercial sources of either. But these are living insects with distinct needs and requirements. It’s probably most efficient for an agency such as the USDA to release and establish them on a community-wide basis.

Several nematodes (microscopic parasitic roundworms) are effective against Japanese beetle larvae. These nematodes burrow into the grub and proceed with their life cycle, reproducing and ultimately killing their host (the grub), at which time more nematodes are released into the soil. For maximum effectiveness, nematodes are applied when the grubs are small (about 2 weeks after the beetles appear, late June to early July in the Midwest) but can be applied until frost. The two nematode species that are most effective against grubs are Heterorhabditis bacteriophora and Steinernema glaseri. The nematodes do not persist well in the soil, however. Preparations of live nematodes of both species are available commercially and easily applied with a watering can or a garden-hose spray apparatus.

Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces an insecticidal protein. It was made famous in the 1990s when the gene for the insecticidal protein was genetically engineered into corn and cotton. There are many strains of this bacterium that are pathogenic to specific insects. There is no specific Japanese beetle strain, but the protein from several strains is active against Japanese beetle grubs. A powered formulation applied to a lawn like a fertilizer is generally available at garden stores or through catalogs.

The most widely used and effective natural control for Japanese beetle larvae is the native North American bacterium Bacillus popilliae. It causes a disease called “milky spore” because of the characteristic milky appearance infected grubs exhibit. The bacterium was first registered for use on Japanese beetle grubs in the USA in 1948. When grubs ingest the bacterial spores, they become infected and die and as many as 2 billion new spores are released into the soil. The bacterium, and hence grub-disease potential, builds up in soil over time (2–4 years). Milky spore disease is effective in suppressing beetle populations. This too is widely available and is spread as a powder on lawns.

The short story is that Japanese beetle is here to stay; sooner or later, it will probably infest all 50 states and much of Canada. We must adapt to it. USDA and other agencies continue to explore control strategies. For the gardener or homeowner, the most effective strategy will be long term and rely on combinations of chemical, cultural, and biological practices. Good luck.

Table 1. Plants resistant to adult Japanese beetle feeding (Source USDA).

Woody plants

Herbaceous plants

Red maple Acer rubrum Ageratum Ageratum spp.
Boxwood Buxus spp. Columbine Aquilegia spp.
Hickory Carya spp. Dusty miller Centaurea cineraria
Redbud Cercis spp. Rose campion Lychnis coronaria
Tulip poplar Liriodendron tulipifera Begonia Begonia spp.
Dogwood Cornus spp. Lily of the valley Convallaria majalis
Burning bush Euonymus spp. Coreopsis Coreopsis spp.
Forsythia Forsythia spp. Larkspur Delphinium spp.
Ash Fraxinus spp. Foxglove Digitalis spp.
Holly Ilex spp. California poppy Eschscholzia californica
Juniper Juniperus spp. Coral bells Heuchera sanguinea
Sweetgum Liquidambar styraciflua Hosta Hosta spp.
Magnolia Magnolia spp. Impatiens Impatiens spp.
Spruce Picea spp. Lantana Lantana camara
Pine Pinus spp. Forget me not Myosotis spp.
Red oak Quercus rubrum Pachysandra Pachysandra spp.
White oak Quercus alba Poppy Papaver spp.
Lilac Syringa spp. Moss rose Portulaca grandiflora
Yew Taxus spp. Showy sedum Sedum spectabile
Arborvitae Thuja spp. Nasturtium Tropaeolum majus
Hemlock Tsuga spp. Violet, pansy Viola spp.

Table 2. Plants susceptible to adult Japanese beetle feeding (source USDA).

Woody plants

Herbaceous plants

Japanese maple Acer palmatum Hollyhock Alcea rosea
Norway maple Acer platanoides Dahlia Dahlia spp.
Crape myrtle Lagerstroemia indica Hibiscus Hibiscus moscheutos
Apple, crabapple Malus spp. Common mallow Malva rotundiflora
Virginia creeper Parthenocissus quinquefolia Evening primrose Oenothera biennis
Plum, apricot,

cherry, peach

Prunus spp. Soybean Glycine max
Pin oak Quercus palustris Pennsylvania smartweed Polygonum pensylvanicum
Sassafras Sassafras albidum Rose Rosa spp.
American mountain ash Sorbus americana Grape Vitis spp.
Basswood (American and European) Tilia spp. Sweet corn Zea mays
Horse chestnut Aesculus hippocastanum Clematis Clematis spp.
Althaea Althaea spp. Gladiolus Gladiolus spp.
Birch Betula spp. Sunflower Helianthus annuus
Summer sweet Clethra spp. Morning glory Ipomoea purpurea
Hawthorn Crataegus spp. Cardinal flower Labelia cardinalis
Beech Fagus grandifolia Peony Paeonia spp.
Black walnut Juglans nigra Asparagus Asparagus officinalis
Larch Larix laricina Rhubarb Rheum rhabarbum
Lombardy poplar Populus nigra var. italica Red raspberry Rubus idaeus
Willow Salix spp. Zinnia Zinnia spp.
This entry was posted on Tuesday, March 23rd, 2010 at 2:23 pm and is filed under Original Posts. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.
Follow Comments:
RSS Feed for This Post

30 Responses to “Meet The Beetles: Frederick Dobbs on Japanese Beetles”

  1. bill gaisser said:

    one of the most beautiful woody plants, the climbing hydrangea…is also susceptable…i’ve lost several to japanese beetles over the years

    • Frederick Dobbs said:

      Dear Bill, Japanese beetles are pretty nasty critters, aren’t they.

  2. Ken Lamb said:

    Is there any kind of bird that likes to eat these beetles? Thanks, Ken

    • Frederick Dobbs said:

      Dear Ken, My understanding from a Cornell University extension website ( is that starlings eat the beetles and several other kinds of birds eat the grubs. It’s only a guess, but I’d bet that chickens also would eat the beetles. I’ve never heard of birds being used as an effective control agent, though.

  3. Mária White said:

    Wow! Thank you for this thorough treatise on “everything I’ve always wanted to know about the Japanese beetle.”

    • Frederick Dobbs said:

      You’re quite welcome, Mária. Hope you can use it.

  4. Inez said:

    Thank you very much for this informative piece on the Japanese Beetle. Bring on more info that HELPS us in our garden; helps us to grow organically; helps us improve our soil; helps us attract beneficial insects and butterflies to our garden; helps us be better keepers of the environment for our limited time on this earth.

    Thanks, this is a keepable article.

    • Frederick Dobbs said:

      Dear Inez, Thanks for your kind words.

  5. Kathy said:

    Please post pictures of the pest and examples of the damage so I can know if I have this pest.
    Thank you,

    • Frederick Dobbs said:

      Dear Kathy, Please go the following link for pictures of the beetles and feeding damage (Japanese beetles pictures). There are probably more there than you want.

  6. Judy said:

    I’ve been picking Japanese beetles off of plants since I was a kid 50 years ago. I’ve done the milky spore, and yes, traps do attract more to your yard. I find a combo of milky spore and nematodes works well, but they tend to hatch on a warm late June afternoon, when you can hand pick many. Rugosa roses are a fine trap (a friend was correct in saying they are attracted to Asian plants). Just find their favorite plants in your yard and dump them into soapy water early am and sunset while you’re admiring the rest of your garden.

    • Frederick Dobbs said:

      Thanks for your input, Judy. My experience is that hand picking works fine early in the season, but by mid July it’s like bailing a leaky boat with a sieve.

  7. Jaie Shafer said:

    Here in Fairfield Co, CT (Ridgefield) I have not been excessively bothered by the beetle for a number of years, but many years ago (40?) I spent a lot of time putting the milky spore disease down on the lawn area around my flower borders. Apparently the disease has spread since then because I really don’t see much Jap beetle activity. Oh – just at the beginning of July when the roses are about finished their first bloom I do see beetles, but nothing like what I remember seeing those many years ago. So I would suggest putting down milky spore powder (at a teaspoon every 3 feet I seem to remember) but to reap the rewards you need to stay put at your present home for decades. I have been here and gardening since 1969, and the rewards are great after 40 years – the rocks are even gone from my long borders!

    • Frederick Dobbs said:

      Dear Jaie, I’d like to see your garden. I spent part of my childhood in Litchfield County, so I know your area a little bit. I wonder if you don’t see many beetle because of your efforts, whether populations are reduced because of the insect Japanese beetle predators that are (now) endemic to your area, or a combination of the two. I haven’t seen any verification of this, but my guess is that the beetles are particularly devastating in area that they’re recently infested, such as the Upper Midwest.

  8. Nancy said:

    I think these beetles are what we here in South Texas call “June bugs”. I find large grubs in my lawn and flower beds when I till. I collect them in a dish then set them out for the birds. The grackles love them. I also have help from the armadillos and skunks. But that has some drawbacks…the armadillos dig big holes and the skunks, well, you know. I plan on trying the milky spore this year.

    • Frederick Dobbs said:

      Dear Nancy, My guess is that what you’re calling a “June Bug” is what is also called a “May Bug”, and it is not the same as a Japanese beetle. There are June bugs in the East and Midwest too. June bug and Japanese beetle do have in common a “white grub” stage in their life cycle, and an infestation of June bug larvae (grubs) can be destructive to turf. The different grubs can be distinguished. Now, you may not be terribly interested in doing so (and I understand), but the following link documents the distinctions and shows you how to tell the two bug apart:

  9. M.E. Wells said:

    The article was very interesting as well as informative. We have used ‘Bascillus Popillea’ (milky spore) in the past and the application was very back-breaking, not to mention straining the neck, having to bend over to apply the powder every 2′ square on the lawn, even with the available aide of an applicator. When you said,”… spread as a powder on lawns”, do you mean you can provide it the same way as granual lawn feeds, etc.? I would be very happy if you would respond to this question. Thanks for the great article and hope to hear from you soon.

    • Frederick Dobbs said:

      Dear M.E., I was a little misleading. You’re correct that there’s no lawn spreader that would properly meter a powder like this. But where it’s important to spread a fertilizer evenly over the lawn, that’s not necessary with the milky spore powder. Most instructions that I’ve seen recommend that a teaspoon, or whatever the concentration warrants, be placed on top of the grass every 4 feet in rows 4 feet wide (this, like the concentration of the preparation may vary with manufacturers). It may still be a pain in the neck, but you don’t need to worry about getting the powder on every square inch. The powder is just a carrier for the bacterial spores. These spores are resting structure for the bacterium. They are very resistant to heat, cold, moisture stress, and even ultraviolet radiation. It is the spores that the Japanese beetle grubs ingest and that germinate inside the grub. Once the spore has germinated, bacteria reproduce inside the grub and more spores are formed. When the grub dies, the spores are released into the soil, multiplying their concentration. Ideally, the concentration of spores in a lawn will continue to increase.

  10. Terry Katz said:

    Thanks for the helpful info on Japanese beetles. You write some interesting pieces!
    terry katz/reporter/Sturgis Journal

    • Frederick Dobbs said:

      Thanks very much, Terry. Hope it’s useful to you.

  11. Gary said:

    An Excellent article on Japanese Beetles, when I first planted new roses I had a ton of Japanese Beetle. As the years go on there seem to be less of them…and they are there for only a few weeks. Thank God….. I think you have given me some new ideas. Thanks for the great information.

    • Frederick Dobbs said:

      Thanks, Gary. I hope your luck holds.

  12. Debbie said:

    I have found spraying plants with deer repellent makes plants less appealing to Japanese beetles. Not practical for trees, but works on my crape myrtle and smaller plants.

    • Frederick Dobbs said:

      Dear Debbie, Thank for the tip.

  13. MJ ORourke said:

    Thank you for the informative and interesting article on Japanese beetles. I feel armed for the struggle this year.

    • Frederick Dobbs said:

      Good luck, MJ.

  14. My sister in law has had problems with the japanses beetles in the past. Now she uses some type of organic pesticide type spray which takes care of them. I am not fully sure what it is called, but I will find out.

    • Frederick Dobbs said:

      Dear SOGT, Thanks for your comments. It would be interesting to know what she uses, particularly since it sounds as though it’s effective.

  15. Raina said:

    Just wanted to say thank’s for a great article and the listings of plants that may be resistant. I live 40 miles west of Chicago and the last three years I was horrified have witnessed a huge increase in these beetles as have my neighbors, those that garden. They will devour those plants, trees, and shrubs favored first, as they finish they move onto those less favored, and was told by my local nursery that they will eat any and everything, depending on how large of an infestation there is (we have Himalayan birches). (paragraph 9)

    We do treat the ground, and do spray the trees, use Milky Spore (takes a few years to see benefits I am told), I handpick and drown in soapy water what I can reach every morning and evening (no traps please, they should be banned!!!!) – it becomes a mission. I also prune the buds of those favored roses and do cover those plants that I can which seems to help, but you still have to pay attention to the leaves…and then ofcourse they just keeo flying in. (My best friend uses pyola and had luck. She has a small yard yard though and uses almost solely a natural approach with nematodes and other remedies, and chemical only in absolute desperation. We will also cover her flower cutting beds this year.)

    Treating them is also difficult because those neighbors with grass do not treat, it really needs to be a community effort (neighbors banding together and like minded) otherwise may cancel out your hardworking efforts -it’s an uphill battle. (See your paragraph 10)

    I grew up in the East and was aware of this beetle in my mother’s roses from time to time, but never to volume that I have experienced these last few years. You can go to various subdivisions many miles away and see trees “chewed” up. I will look forward to the day we can really have some effective on the beetle, one the doesn’t have conseqences to the environment. It is a work in progress to settle on those applications that work for you against this beetle and look forward to what research comes up with (paragraph 12-16)

  16. Toni Roberts said:

    I’ve been using Bayer Tree and Shrub systemic insecticide for 3 years on my plants that are most attractive to Japanese beetles. I apply it in April and it has greatly reduced damage to my Harry Lauder’s walking stick, hybiscus, and Wildberry rose. Definitely worth a try!

Follow Comments:
RSS Feed for This Post