The Japanese Beetle WebSite

Controlling These Pests

The spread of Japanese Beetles has been steady over the last 80 years since their introduction in New Jersey since they left their natural diseases, parasites, and predators behind in Japan. The United States and several individual state Departments of Agriculture has tried to control the spread with a quarantines of infested areas. Plant producers in infested areas must inspect and certify any shipment containing soil which leaves their area bound for Japanese Beetle free areas. Sometimes containers must be treated and quarantined before shipments can be made. This may have slowed the progress of these pests, but it has not stopped their migration across the country.

Natural Methods

Several natural methods help keep down the populations of Japanese Beetles. Some types of wasps kill them. Many species of birds eat them - being especially font of them in their grub stage. Raccoons and possums like to eat them. Dry weather during their egg stage can reduce their population (so avoid irrigation of nesting areas during this season wherever possible). And planting only varieties of plants which are not food sources that attract the beetles helps keep them away. (The University of Kentucky web site has a list of plants less attractive to beetles.)

Biological Methods

A couple of biological controls are commercially available although their effectiveness is questionable. The longest available and easiest to find is Milky Spore Disease (Bacillus popilliae Dutky and B. lentimorbus Dutky). The grubs become infected when they ingest the bacterial spores while eating roots. Over a period of several weeks the spores germinate into bacteria infecting the grub, form billions of white spores in the grubs blood, and kill it. This is reported to have been effective in some areas although recent tests in both Ohio and Kentucky have not shown it to be beneficially effective over periods of 1 to 4 years in controlling Japanese Beetles outside the laboratory. To be effective the beetle population should not be controlled by any other means (which translates into letting them eat up your plants for one year!) since there must be live grubs present for the spores to infect and feed on to spread the disease throughout the ground. The type of soil may play a role in the effectiveness of Milky Spore Disease and so further testing is necessary to determine where it works and where it does not work in controlling this pest.

The second, and soon to be commercially available, biological control is Entomophagous Nematodes. Several have been tested as far back as the 1940's including Steineranema (=Neoaplectana) glaseri and S. carpocapsae. The newest and reportedly most effective nematode is Heterorhabditis spp. which when applied shortly after the eggs hatch and well watered into the soil has been effective. The nematode enters the grub through its mouth and releases the bacteria Xenorhabdus poinarii into the grub's blood stream. The grub then dies within 24 hours. It has been shown to kill up to 50 percent of the grubs in a 100 square foot university test plot.

Chemical Methods

There are, of course, commercial pest control chemicals that can be used to stop these varmints from devouring the fruits of your many hours toiling in your garden. Perhaps the least harmful of these is commonly known as Sevin so long as the spray residue remains on the leaf surfaces. Sevin has the capacity to decompose in a few days time which will allow safe harvest of most fruits and vegetables after just a few days (be sure to carefully read your label to determine the correct waiting period since it varies by crop). However Sevin should not be used on crops (such as green beans) where beneficial insects such as bees are also present pollinating the blossoms during the period of beetle infestation since they will be killed also. The bees actually gather the power residue like pollen and take it back to their hive to feed their larvae; this can cause major damage to the hive's bee population.

Chemicals do little to control these pests on flowers that attract them. Sprays and powders usually do not get inside the blossom where the beetle feeds and so have little effect on the beetle.

Some long residual life pesticides in the pyrethroid family (like Astro, Decathlon, and Talstar) can protect leaves for as long as three weeks. Other pesticides used against Japanese Beetles include Carbaryl (carbamate), Isazophosphate (organophosphate), Cyfluthrin (synthetic pyrethroid), and Isofenphos. (For a good listing of chemical controls and their side effects see the University of Kentucky Japanese Beetle pages.)

Organic Methods

The organic remedy of spraying plain soapy water on your plants is helpful in controlling many small garden pests. But this is not very helpful in the case of Japanese Beetles. Just plain catching them, especially if done several times each day, may offer the best hope for blooming plants - such as roses and hollyhocks where it is almost impossible (or undesirable) to put chemical controls inside the freshly opening flower buds - where these pests love to congregate inside the flower itself and gorge themselves.

One gardener reports success at killing Japanese Beetles by dusting their plants with self-rising flour from their kitchen. The bugs ingest the flour while feeding on the plants (causing some plant damage) and then die when the baking powder in the flour reaches their acidic stomachs and burst their digestive tract! It was reported that the next day after such a dusting numerous dead beetle lay on the ground around the where the flour had been used. (I would be interested in hearing from anyone who tries this control method or who has other organic methods which they have found to be successful. Just send me an E-Mail note.)

Trapping Methods

Although popular the commercially available traps may not be an effective control. These traps combine the use of two scent lures. The first is an aggregation pheromone given off by all Japanese Beetle which causes them to congregate in large numbers in one place once a single beetle begins to feed on a favorite food plant. And the second is the sex pheromone given off by those virgin females which is so attractive to the male beetles.

Colorized Drawing of Japanese BeetleThis combination proves very good at luring other Japanese Beetles to the area of the traps. But the lure's effectiveness may be as much of a problem as a cure. While the trap may quickly fill with bugs, not all of those drawn by these scents will become trapped - especially once the smell of dead and decaying beetles makes the trap itself as repulsive to newly arriving beetles just as much as it is to humans nearby. So they continue to be drawn to the general area of the trap, but not into it. Once in the area the beetles may begin feeding on your prized plants and mating with other beetles brought there by the same attractants.

Results of tests performed by leading universities have shown that neither traps nor trap captures are effective in reducing local grub populations. The most effective they have shown to be is a reduction of only 30 percent and that is when used over a very large (neighborhood sized) area. And in some tests, such as those by Dr. Dan Potter of the University of Kentucky, there has actually been an increase in the amount of damage to plant leaves by the adult beetles drawn to the area where these traps have been placed since traps are better at drawing beetles than at trapping them. One or two traps in a residential sized lot only draws additional beetles to the site. It might take the involvement of a whole neighborhood to be effective in reducing beetle damage by trapping ... and even that might prove to be counter-productive by being a stronger draw from an even wider area.

It has been humorously suggested that traps are most effective if given to your neighbor to place in their yard! In any case, if traps are used they should be placed well away from any plants that need protection from Japanese Beetles and the bags should be emptied and washed daily to reduce the repulsive odors of the dead bugs.

Catching Japanese Beetles in the Act

Just plain chasing Japanese Beetles off your prized plants - even if you don't kill them - can have some beneficial effect. Even a single beetle on a plant will attract more beetles. They give off scents (especially female beetles) which will cause other beetles to come swarming to join them on your favorite plants. And while a single Japanese Beetle may do little real harm to the plant, the hordes which follow can actually kill smaller plants. They will usually start feeding at the top of the plant and eat their way downward skeletonizing the leaves as they go.

For several years I ... and many other gardeners whom I have seen as I drove down the road ... have filled a pint sized jar or can with soapy water and walked around the yard and garden catching Japanese Beetles. The warmer the temperature the more active and harder to catch these bugs become.

But these beetles have one trait that makes them fairly easy to capture: When first disturbed Japanese Beetles will release their hold on a leaf and free fall downward before taking off in flight. So if a person carefully holds a container just under the bug's perch before gently disturbing the pest it will drop down into the container.

Drawing of beetle catcher bottleThe soapy water in the container will disable the beetle from crawling out and flying away. Plain water will not do the trick; one beetle will just climb up on top of another beetle and escape. However, if left in the soapy water overnight the bugs will die and can be just poured out on the ground to serve as compost ... although very many dead bugs together start to stink pretty bad.

This season I have designed a container to catch Japanese Beetles without using soapy water which can spill water or even the pests themselves. This makes the task easier and the container lighter to handle.

To make my Beetle Catcher Bottle I used a pair of two-liter plastic soda bottles. One bottle was cut around its circumference at the point where the opening widens out to the full diameter. The cut bottle was then turned up side down (forming a funnel) and attached on top of the intact bottle - open neck opening to open neck opening. This arrangement is pictured in the accompanying diagram. To hold them together I slid the threaded parts of the neck of each bottle into either end of a 1-1/2 inch long section of 1 inch plastic pipe which I had split down one side to allow it to expand slightly. Then I spread hot glue all around the threads under the section of pipe to keep the two bottle openings securely together.

My new Beetle Catcher Bottle works well because it allows Japanese Beetles to be captured without fear of them flying away due to the small neck opening while the funnel channels the falling bugs right into the main capture chamber. After catching all the beetles I find in my yard and garden I add soap and water to the bottle and let it stand over night to kill the bugs; the next morning I dump them out and rinse the bottle to keep it smelling fresh and clean for the next use.

What are Japanese Beetles?
Where do they Come From?
Controlling these Pests
Catching Japanese Beetles in the Act
Links to related sites

Latest Update on May 24, 1998 by HTML coding by Roger Baxter.

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