The Japanese beetle is a highly destructive plant pest that creates havoc for lawns, golf courses, and agricultural plants. Originally native to the Japanese archipelago, this shiny, metallic-green insect arrived in the United States in the early 20th century and has since become a major nuisance for gardeners and farmers alike.
Feeding on more than 300 different types of plants, the Japanese beetle attacks foliage, flowers, and fruit, causing significant damage and sometimes even destroying entire crops. Homeowners and landscapers must be vigilant in detecting and controlling these pests to prevent costly consequences.
Part of the challenge in controlling a Japanese beetle infestation is recognizing their various life stages. Adult beetles feature bronze-colored outer wings and distinctive tufts of white hair along their body. Knowing how to identify and manage each stage of the beetle’s life cycle can help curb their damaging presence.
Japanese Beetle Overview
The Japanese beetle (Popillia japonica) is a striking insect, characterized by its bright metallic green head, thorax, and abdomen. Some other features include:
- Dark green legs
- Brown wing covers
- White tufts of hair along the sides and back of the body
- Males are smaller than females
The lifecycle of the Japanese beetle consists of four main stages:
- Eggs: Laid in the soil by adult females
- Larvae: C-shaped white grubs that feed on grass roots
- Pupae: Inactive stage, transforming from larvae to adults
- Adults: Active, feeding on foliage, flowers, and fruits
Here’s a brief comparison of larvae and adult beetles:
|Metallic green head, thorax, abdomen
|Feed on grass roots
|Feed on more than 300 different ornamental plants
In conclusion, the Japanese beetle is a highly destructive pest with a distinct appearance and lifecycle, making it important to be able to identify and understand its behavior.
Distribution and Impact
United States Infestations
The Japanese beetle, an invasive insect native to Japan, was first introduced to the United States in New Jersey in 1916. Since then, it has spread widely throughout most of the eastern United States, reaching the Mississippi River, and some western states including Arkansas, Kansas, Minnesota, South Dakota, and Oregon.
- Eastern States: Widespread infestations
- Western States: Limited infestations
This beetle can cause significant damage to grass roots, resulting in harm to lawns, golf courses, and pastures. Additionally, Japanese beetles feed on the foliage, flowers, or fruits of more than 300 different ornamental and agricultural plants, impacting both landscape and crops.
Quarantine and Regulations
To prevent further spread and mitigate their impact, quarantine and regulations have been established:
- Oregon is currently implementing a Japanese beetle eradication project, targeting areas with lawns and ornamental planting beds.
- Treatment for Japanese beetles typically occurs from April to July, consisting of up to two treatments.
|April – July
By following these measures, authorities aim to minimize the Japanese beetle’s impact on plants, crops, and overall ecosystem health.
Host Plants and Feeding Habits
Favored Plants for Feeding
Japanese beetles preferentially feed on a variety of plants. Some examples of their favored woody plants include:
- Mountain ash
For crops and other landscape plants, they target:
- Garden vegetables
Japanese beetles tend to avoid certain plants as well. One way to limit their impact is by selecting plants they usually avoid, such as wild weeds 1.
Feeding Damage Patterns
Japanese beetles damage plants in various stages of their lifecycle. The grubs harm grass roots, affecting lawns, golf courses, and pastures. They also attack host plants, including turf and yard plants (like turfgrass), as they seek moist soil to lay their eggs 1. Adult Japanese beetles feed on more than 300 different host plants, targeting their foliage, flowers, and fruits 2.
|Damage grass roots, lawns, golf courses, pastures.
|Lawns, golf courses, pastures.
|Damage foliage, flowers, and fruits of host plants.
|Roses, maples, beans, corn, vegetables
Natural Predators and Parasites
There are several natural predators and parasites that can help control Japanese beetles, such as:
- Tachinid flies: These flies lay eggs on adult beetles, and the larva consumes the beetle from the inside.
- Spined soldier bugs: These insects prey on Japanese beetle grubs in the soil.
Including plants like marigolds and larkspur can also attract predatory insects.
Insecticides can be applied to lawns to control both larvae and adult beetles. Examples include:
- Imidacloprid: Targets larvae in the soil
- Carbaryl: Effective against adult beetles on plants
- Kills larvae and adult beetles effectively
- Protects plants from damage
- May harm non-target insects
- Requires regular applications
Traps can be used to capture adult beetles, using pheromones and floral lures. Examples include:
- Japanese Beetle Trap: Attracts beetles, catches them in a disposable bag
- Reduces the adult beetle population
- No chemicals needed
- May attract more beetles to the area
- Doesn’t address larvae in the soil
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Japanese Beetle on Cannabis
Subject: Is this Japanese Beetle going to eat my medical marijuana?
Geographic location of the bug: Ohio
Time: 12:28 PM EDT
Your letter to the bugman: Dear Bugman,
The Japanese Beetles were terrible this year. They ate all the leaves off my neighbor’s ornamental plum tree. They decimated the roses, and at times they seem to want to eat everything in sight. They ate my friend’s hawthorn. I keep finding one or two when I inspect the medical marijuana I just started growing this year, but they don’t seem to be eating the plants. I have tried to research Japanese Beetles and marijuana and I was thrilled with your section on Insects and Cannabis called What’s on my Woody Plant?
So I expect my girls to start producing buds soon. Do I need to fear the Japanese Beetles eating my marijuana?
How you want your letter signed: Paranoid Pot Grower
Dear Paranoid Pot Grower,
Time may be on your side, especially since the Japanese Beetles you are finding do not appear to be eating the leaves on your plants. According to BugGuide: “Larvae feed on roots of many plants. adults feed on more than 350 different species of plants, but are especially fond of roses, grapes, smartweed, soybeans, corn silks, flowers of all kinds, and overripe fruit.” Your buds are flowers, so they might be attractive to the beetles if there is no other preferred food to be eaten. BugGuide also states Japanese Beetles are active “mostly: June-Sept” and we suspect your harvest will be after late September, so you shouldn’t have to worry about loosing your entire crop. According to Holy Moly Seeds, Japanese Beetles eat: “Mainly roses, grapes, cannabis, beans, strawberries, tomatoes, peppers, grapes, hops, cherries, plums, pears, peaches, berries, corn, peas, and many more. They feed on the foliage of the plant, eating the material in between veins.” According to Medical Marijuana (Cannabis sativa x indica): “Japanese beetles will eat the entire leaf. Just like home gardens a population of Japanese beetles can kill a whole plant by destroying its leaves so badly it cannot photosynthesize enough to support itself” but you do not seem to be experiencing that. Medical Marijuana Cannabis Pests says nothing about leaves and buds, but it does state: “The most serious root pests are flea beetle grubs (Psylliodes attenuata) and white root grubs — Japanese beetles (Popillia japonica) and chafers (Melolontha hippocastani and M. melolontha).” Please give us an update if you do find the Japanese Beetles are eating your buds.
Letter 2 – Buckets and buckets of Japanese Beetles collected in Ohio
Subject: Invasion of the Japanese Beetles
Geographic location of the bug: Campbell, Ohio
Time: 07:11 AM EDT
Those of you who are new to this site don’t know that there was a period of time when Daniel would respond to 20 or more identification requests per day. Now Daniel does all he can to avoid working on the computer, preferring instead to work in his gardens. Right now he is working in his inherited homestead in Eastern Ohio where large lawns with no trees or shrubs or flowers are popular with much of the population. Lawns are the breeding grounds for the grubs of the dreaded, invasive Japanese Beetles, which were accidentally introduced to the eastern states in 1917 with imported horticultural specimens. Gardeners’ preferences for exotic plants over native plants will likely never be fully altered, but that matters not with Japanese beetles that feed on over 300 species of plants, many of them native. They have proliferated without any natural enemies and daily, now that it is Beetle Season, Daniel picks beetles by the bucket.
Daniel puts about an inch of water in a plastic bucket and adds a squirt of dish soap. To that he adds a few drops of motor oil. It is best to collect Japanese Beetles early in the morning or at dusk because they are most active and more likely to take flight when disturbed if it is sunny. When they are less active, they tend to drop when disturbed and if the bucket is under them, they drop into the bucket. They die within a few minutes.
It is hard to believe that the first Japanese Beetle of the season was sighted a few short weeks ago on June 16, and that beetle was quickly squashed between Daniel’s fingers. Beetle season is expected to last a few more weeks and many leaves in the garden look, in Pearl’s words, like “lace doilies.”
For new readers, it should be noted that Daniel is against unnecessarily killing most insects, but Invasive Exotic species that have no natural enemies are fair game. Daniel dreads the eventual, inevitable introduction of the Spotted Lanternfly or White Cicada to his garden since they have already been reported from Pittsburgh, a mere 60 miles from Campbell.
Letter 3 – Bug of the Month July 2010: Japanese Beetles
June 24, 2010
Hi Daniel, You asked for images of Japanese Beetles. I had a few but none were very good, so I took some more today. Not really pleased with these either, don’t know why but my camera doesn’t seem to focus on them very well. Perhaps they are clear enough for an ID. I never cropped one very close to show the “lace leaf” you were talking about, this is a grape leaf. I hope you are able to use these. Thank you and have a great day.
North Middle Tennessee
Hi again Richard,
With all due respect, if you were our photography student, we would tell you that you are nuts. This photo has everything. We especially love that it shows the leaf damage caused by the beetle, which our mom in Ohio compares to lace doilies. The two pairs of beetles on the right appear to be mating. While the focus on the right of the image is not critically sharp, it is more than acceptable especially considering the detail in the Japanese Beetle in the upper left. We also appreciate that you managed to send us photos of all the insects we saw in Ohio earlier in the week that we lamented not having had a camera so we could take our own: The Question Mark, Great Spangled Fritillary, and Firefly as well as the Japanese Beetles. We are upgrading the status of this posting to the Bug of the Month for July.