How To Control Japanese Beetles

The Japanese beetle, Popillia japonica, is a highly destructive nonnative plant pest that has become a threat to American agriculture. Homeowners encounter this pest during the summer months as the adults fly and aggregate in clusters to feed upon plant leaves. These skeletonized leaves, missing soft leaf tissues, are a tell tall sign of Japanese beetle activity. If you are having problems with these insects then continue to read and learn about their life cycle, what they like to eat and finally methods of control.

Adult Japanese beetle

How to control Japanese beetles begins with understanding the insect’s life cycle.  The life cycle of a beetle is known as a complete metamorphosis, meaning it has four very different stages: egg, larval, pupal and adult. The eggs are laid in the soil about two to four inches down where they can absorb moisture. A female can lay about 40 eggs over her entire lifetime. Eventually, these eggs develop into beetle larvae or grubs which feed on the roots plants and grasses. The larvae are typically white in color and go through several molts. Larvae are mobile and can become so numerous that they often destroy lawns and turf in golf courses.  Larvae will then pupate, change color and transform into adults which leave the soil and begin to immediately search for food.

As adults,  Japanese beetles are also destructive plant pests. According to the United States Department of Agriculture (USDA), adults forage on the leaves and fruits of several hundred species of trees, shrubs, vines, and vegetables. A telltale sign of their presence is skeletonized leaves and large, irregular holes. The Japanese beetle is considered the most widespread turf-grass pest in the United States.

As we mentioned earlier, the Japanese beetle is a nonnative or invasive species, an organism outside its native distributional range that was most likely introduced by human activity.  The Japanese beetle is native to eastern Asia, however, it was first found in the United States in a nursery in southern New Jersey in 1916 probably coming over with a shipment of ornamental flower bulbs. Since this organism had no native biological controls their populations exploded as seen by the USDA map below.

Japanese Beetle Distribution Map
The Japanese beetle has become a serious plant pest and a threat to American agriculture.

Integrated Pest Management (IPM) comes from the idea that if a pest population is targeted then beneficial insects and other organisms in the environment will be impacted as well. So IPM serves as a means of controlling pest population to levels that lessen their economic impact. It is not the eradication of an invasive species rather IPM can be implemented using biological, chemical, cultural and mechanical methods that are complementary to each other. It is important to understand that using an integrated pest management approach will not completely eliminate Japanese beetles from your property.  These particular insects are here to stay, we just need to minimize its impact on our environment.

Although the Japanese beetle feeds on almost 300 species of plants, it feeds sparingly or not at all on many cultivated plants. The various kinds of plants on your property can significantly influence the susceptibility of your property and plants to Japanese beetle damage.

Wood Plants Resistant to Adult Japanese Beetles
Hemlock Yew Northern red oak Pine
Arborvitae Spruce Magnolia Sweetgum
Juniper Holly Ash Forsythia
Dogwood Redbud Hickory Boxwood
Herbaceous Plants Resistant to Adult Japanese Beetles
Violet Nasturtium Sedum Poppy
Forget-Me-Not Lantana Impatiens Hosta
Foxglove Larkspur Coreopsis Lily of the valley
Begonia Dusty-Miller Columbine Ageratum

Pesticides which are useful against adult beetles include Permethrin, Deltamethrin, and Bifenthrin. Homeowners and gardeners need first to assess the risks and benefits of pesticide use. This includes application timing, toxicity, and the fate of pesticides in the environment.

pyrethrin chemical structure
Pyrethrin chemical structure is modified to produce insecticides effective against the Japanese beetle’s nervous system.

Biological controls include, Heterorhabditis bacteriophora, is a species of entomopathogenic nematode known commonly as beneficial nematodes. They are microscopic and are used in gardening as a form of biological pest control against Japanese beetles.

A naturally occurring soil bacterium called Bacillus thuringiensis or just Bt is used as a microbial insecticide. The Bt strain used for the Japanese beetle is for grub stage only. Bt is an insect digestive system poison that must be ingested to be effective.

Mechanical traps can easily capture thousands of Japanese beetles. This trapping method is an easy and inexpensive way to reduce beetle populations and reduce egg laying. According to the USDA, under favorable conditions, a trap will capture approximately 75 percent of the beetles that approach it. Because these traps attract more beetles than they capture, be sure to place traps away from your favorite plants and vegetable garden. Not only are you attracting and capturing adults on your property but also from the surrounding area. So install traps at the borders of your property. Trap placement should be timed to coincide with the emergence of adult Japanese beetles in your area usually between early June and late August.

japenese beetle lure
A chemical lure using floral volatiles to attract males and females. Additionally, it contains a sex pheromone to attract male Japanese beetles.

Integrated Pest Management to Reduce Japanese Beetle Populations

  • Remove older fruit from the ground, the odor of such fruit will attract beetles
  • When considering new plantings use trees, shrubs, and other plants that are not preferred by the beetle.
  • Make use of both chemical and biological controls
  • Use of mechanical traps baited with sex pheromone and floral volatiles

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.