Dealing with Japanese Beetles

Dealing with Japanese Beetles

Posted by Jessie Jacobson on Jul 4th 2024

Dealing with Japanese Beetles

Japanese beetles were introduced in the early 1900's and are an invasive insect in the United States. These beetles feed on the leaves, flowers, and fruit of over 300 plant species. Their favorites in our area include Linden trees, roses, grape vines, potato vine, and coleus, but they will really eat anything!

Population numbers fluctuate from year to year, with beetles feeding for six to eight weeks beginning in mid to late June. Adults can fly several miles between feedings and are attracted to feeding-induced odors and potent sex pheromones. This often results in large clusters of beetles on some plants while neighboring plants are only lightly infested.

The Japanese beetle and has no known predators in its adult stage that are aggressive enough making it difficult to get the large numbers of these destructive beetles under control.


Life Cycle


Female beetles lay between 40 and 60 eggs over the course of their adult life. Eggs are exclusively laid in sunny turf grass areas.


Beetle eggs hatch in late summer and the prevailing grubs immediately begin feeding on the roots of the turf grass where they were laid. In heavy feeding areas, irregular shaped brown patches form that lift when pulled up. This damage is usually seen in late summer or early fall. Grubs also attract animals such as raccoons, skunks, and moles which dig up our lawns in search of their next meal.


Larva go through 5 instars (the stage between each molt) underground before overwintering 4"-8" below the surface. Grubs return to the surface and continue to feed on turfgrass in early spring until mid-summer when pupation occurs.


Adult beetles emerge from the ground in late June and early July when the life cycle of feeding and laying eggs begins again. Adults are 1/3” to 1/2” long with a metallic green head and thorax and metallic copper-brown wing covers.

Signs and Symptoms

Leaves appear skeletonized with intact veins, holes in flower petals, stunted plant growth, clusters of brown, dry patches on leaves.

Management and Treatment

  • Be out there, be watching. Know how to identify the beetle and the damage they cause. Once feeding starts, it lasts for 6-8 weeks.
  • Knock down the population. Don’t delay in taking care of them, it just gives them time to increase their numbers.
  • Hand pick and toss beetles into a bucket of soapy water. Do this a couple times per day when they first emerge because new beetles are continuing to hatch and appear at this time. Zen out with a cup of coffee of you favorite adult beverage while picking beetles for ultimate enjoyment.
  • Spray Japanese Beetles with an insecticide sparingly. Reserve for high value plants where damage is extreme. Bonide’s Japanese Beetle Killer, Eight, and Captain Jack’s Dead Bug Brew are all good choices. Spray very early in the morning or late in the evening when pollinators are not active, avoid spraying blooms for pollinator safety (if possible, enclose blooms in baggies for extra protection), and try to hit the beetles directly.
  • Beetle Baggers are another option. And it’s true that the baggers attract beetles, so your neighbor’s beetles might end up in your yard. However, the point is to place it away from their favorite plants to lessen the damage plus kill the beetles and stop them from laying more eggs.

Finally, a Natural Enemy

Two natural enemies of Japanese beetles have recently been released in Minnesota. The parasitic fly Istocheta aldrichi lays eggs on adult female adult beetles in summer. This fly can lay one - three or more eggs on each beetle. One parasitic larva will survive to kill the beetle within a few days of egg-lay and bore through the host cuticle to begin feeding. The wasp Tiphia vernalis parasitizes grubs in the spring. While this biological treatment is effective. Populations of parasitoids have not been large enough to stave off the invasive nature of our foe, the Japanese beetle.