Everything you need to know about Japanese Beetles. They attack by land and by air.
Japanese beetles are one of our country’s most destructive insect pests, tunneling underground to eat turf roots and flying through the air to find leaves to devour. The USDA estimates that we spend $460 million battling them each year.
When do Japanese beetles appear? What are their favorite foods? How can you control them? These are some of the questions we’ll answer in this article.
When do Japanese beetles appear?
Look for Japanese beetles to emerge from the ground in mid-June in the South. As you move toward cooler climates, they come out later. In the northern states, they may not appear until early July.
Where are Japanese beetles found in the U.S.?
Japanese beetles were accidentally introduced to the United States before plant inspections were mandatory, and were first spotted at a New Jersey nursery in 1916. They have since invaded most of the eastern states.
Japanese beetles are well established from Maine to Georgia, west to Arkansas, and north to Minnesota. Relatively small populations exist in South Dakota, Texas, and Mississippi, while conditions in Florida and Louisiana haven’t enabled the beetles to gain much of a foothold.
In the western states, summers are generally too dry for Japanese beetles to complete their life cycle, though residents there take Japanese beetle sightings seriously and deal with them proactively.
What do Japanese beetles look like?
Adult Japanese beetles are slightly less than a half-inch long, with metallic green bodies and copper-brown wing covers. Five white tufts protrude from their lower half on each side.
How do Japanese beetles feed?
Adult Japanese beetles like to feed on warm, sunny days. They’ll eat flowers and fruits, but they most commonly eat leaves, chewing around the tough veins and turning the leaves into lace, or “skeletonizing” them. They prefer foliage in full sun. Beetles will often start at the top of the plant or Tree and work their way down.
Japanese beetles tend to feed in groups. Damaged leaves release chemicals that attract more beetles to feed. The beetles themselves also produce pheromones that lure other Japanese beetles in from great distances to feed and mate.
Feeding is most intense for about four to six weeks during peak season.
What do Japanese beetles eat?
Roses are one of Japanese beetles’ favorite foods, and you can look for them there when they first emerge. There are several hundred other species of plants that they’ll also eat. As for Trees, Japanese beetles favor the following:
Hydrangea, Tree Form
American Linden (Silver Linden less susceptible)
Ninebark, Tree Form
Plum (especially Purple-Leaf)
Rose of Sharon, Tree Form
Weigela, Tree Form
What Trees do Japanese beetles avoid?
Japanese beetles tend to leave the following Trees alone:
How many eggs do Japanese beetles lay?
A female Japanese beetle lives about 30 to 45 days as an adult. During that time, she is an eating, mating, and egg-laying machine. She’ll lay between 40 and 60 eggs during that period. She’ll burrow down a few inches into the soil beneath turf to lay her eggs singly or in small clusters.
What do Japanese beetle larvae look like?
Japanese beetle eggs hatch underground, and the grubs eat organic matter and the roots of turf grasses. The grubs are whitish and C-shaped, and by the end of summer, they have reached their full size—about an inch long.
What happens to Japanese beetle grubs over the winter?
Japanese beetle grubs do not mature the same year they’re hatched, but spend the winter as grubs. They simply burrow down deeper in the soil when winter approaches and hibernate during the cold months.
When the soil warms in spring, they resume their activity. Soon they pupate (sort of like a caterpillar when it goes into a chrysalis), and a couple of weeks later they emerge from the ground as adults and start the cycle anew.
What kind of damage do Japanese beetles do?
Japanese beetle adults generally do only cosmetic damage to Trees by eating some of their leaves, though severe infestations can weaken Trees by removing a great deal of chlorophyll.
Japanese beetle grubs can create dead spots in lawn from concentrated feeding on roots.
Do Japanese beetle traps work?
Japanese beetle traps are baited with artificial pheromones to lure in the beetles and trap them in a bag hanging below. The traps are very effective at attracting Japanese beetles. In a heavily infested area, around 10,000 were found in a trap after one day!
However, according to research done at the University of Kentucky, the traps tend to make the problem worse by attracting many additional Japanese beetles to the area that don’t wind up in the traps, but on the plants they are meant to protect.
Japanese beetle traps are good for getting a handle on how many of the pests are in the area, but they are counterproductive for control.
How, then, can Japanese beetles be controlled?
Adult Japanese beetles are difficult to kill with organic pesticides. Safe, low-toxicity remedies like insecticidal soap and hot pepper sprays that work on soft-bodied insects like aphids don’t work so well on beetles, which are encased in their own little suits of armor. More heavy-duty chemical pesticides are necessary to circumvent their defenses. However, these chemical fixes carry risks to unintended targets, such as our valuable bees, as well as countless other precious organisms.
For controlling adult Japanese beetles, we recommend instead handpicking offenders and dropping them in a jar of soapy water. The beetles are sluggish in late afternoon, and you may be able to make a meaningful dent in the population this way if the problem isn’t too severe.
There are other approaches to take to attack the grubs. If dead spots appear in your lawn, and an investigation reveals that Japanese beetle grubs are indeed the cause, there is an organic option you can try. A beneficial nematode called Heterohabditis bacteriophora can be applied to the soil. This has shown some success in controlling the grubs.
You may hear of another organic fix called milky spore disease. It has been less impressive in its results in controlling grubs.
Those willing to use a chemical solution should check out a relatively new product called chlorantraniliprole, which goes by the trade name Acelepryn G® and is sold by Scotts® as GrubEx®. When a Japanese beetle population was discovered in Cedar Mill, Oregon, in 2017, the Oregon Department of Agriculture was granted a court order to apply Acelepryn G® to all 2400 residences there, an indication of the gravity with which this pest is viewed in a state where it is not yet a problem. That the product was deemed fit to use on an entire city is also an indication of its low toxicity to people, pets, and wildlife.
Coping with Japanese beetles
Japanese beetles have established themselves in the eastern United States. Lacking the natural predators they have in Japan, their numbers have exploded, and they do millions of dollars of damage to lawns, plants, and Trees each year. However, this doesn’t mean that you can’t have a beautiful landscape even in Japanese beetle country. Choose Japanese beetle–resistant Trees and plants, handpick the insects as soon as they appear, and use low toxicity pesticides when necessary, and you’ll have a healthy, thriving garden that you’ll be proud to show off!