Do Japanese Beetle Traps Work?

Pros and Cons of Using Lures to Capture Scarab Beetles

Japanese beetle.
Japanese beetle traps cause more problems than they solve. Getty Images/M. & C. Photography

Japanese beetles, those shiny metallic green monsters, are a very destructive bug that can truly wreak havoc on plants, flowers, and roots in gardens. Starting in mid to late June in temperate zones, these beetles hardly discriminate, feeding on more than 300 host plants, including field crops, ornamental trees and shrubs, garden flowers and vegetables, and turf in lawns, pastures, and golf courses.

One recent tool in the war against this polyphage is a Japanese beetle trap, sold commercially and marketed to gardeners. However, Japanese beetle traps hanging in gardens have several drawbacks, most significantly because you might be calling for trouble instead of alleviating it. In most home garden scenarios, Japanese beetle traps are not effective for controlling these pests.

How Japanese Beetle Traps Work

Most Japanese beetle traps are ventilated bags or boxes which contain two chemical attractants: a sex pheromone and a floral lure. Japanese beetles spend their days feeding in groups and mating, and the two chemical attractants in combination do an effective job of luring beetles in large numbers from about a .62 mile (1 kilometer) radius.

The big problem is that studies have shown that these pheromone lures attract far more beetles than they trap—about 25 percent more. In other words, when you hang a Japanese beetle trap in your yard, you are inviting every Japanese beetle in the neighborhood into your yard, but only three-fourths of them will end up in the trap itself. The beetles that avoid the trap will now treat your well-manicured landscaping as a full-service buffet.

When Beetle Traps are Effective

Japanese beetle traps are not entirely without merit. They can be used effectively as a survey tool, to determine whether the numbers of Japanese beetles in an area warrant some kind of control. They also work well for managing isolated beetle populations.

They also have been found to work well for orchards, when a single owner can agree to control large areas. A three-year test with mass trapping systems placed throughout blueberry and elderberry orchards in Missouri trapped 10.3 million adult beetles and decreased the number of adults on plants throughout the season from low to very low levels.

Neighborhood associations might control a problem, if you and your neighbors can agree to place traps throughout the suspected area, beginning in mid-to-late June. If everyone in the neighborhood agrees to hang a beetle trap, that might stop the migration from yard to yard.

Unfortunately, to be effective, the traps need to be monitored at least weekly and cleaned and maintained with fresh lures. To be frank, trap cleaning is a pretty disgusting chore; so that solution is not a perfect one by any means.

Benefits of Traps

One big benefit to using the traps is that the chemicals in the traps aren't harsh, and don't harm any other plant, animal, or insect. The bags are placed above ground so that children or pets can't get to them. The most effective Japanese beetle control method is spraying harsh chemical insecticides on your lawn. If you have kids or pets, this might be a big consideration for you.

If you decide to apply insecticides, you'll need to start when the beetles are first observed and you may need to reapply it multiple times throughout the season. There are other biological and physical controls you can use, such as shaking visible beetles into buckets of soapy water or using a dilution of dishwashing liquid to treat your lawn. That forces the larval stage beetles hiding underground to come up for air, which makes them vulnerable to predators such as visiting birds.

Other Ways to Remove Beetles

Japanese beetles can sometimes be selective with what they eat. If you are planning a landscape design for your property, choose plants that Japanese beetles are known to not like. The most resistant or unattractive plants to the Japanese beetle include American bittersweet, dogwood, forsythia, hydrangea, lilac, paper birch, pine, silver maple, spruce, white poplar, and yew. This can help to keep beetles moving along to find a different spot in the neighborhood to eat.

If you have existing plants that are Japanese beetle favorites, you will have to consider if it makes economic sense to remove and replace those plants versus chemically treating the plants. For example, if you have a flowering cherry tree, consider a kousa dogwood. If you have a linden, consider a red maple instead.

Biological Warfare: Geraniums and Nematodes

Planting geraniums (Pelargonium x hortorum L. G. Bailey) as sacrificial victims for your Japanese beetles has been found to be effective. Japanese beetles are attracted to geranium petals and eating them is an intoxicating experience for them, to the point at which the beetle become paralyzed and easily consumed by predators. After recovery, the silly beetles return to gnaw on your geraniums again, even to the exclusion of other, less toxic plants.

You can also use insect warfare, applying nematodes, specifically Heterohabditis bacteriophora and Steinemema glaseri, to your garden soil. Nematodes actively seek and attack groups of grubs, but they need to be applied in August, near dawn or dusk.