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FloraQuest 2011: If We Cantelope, Lettuce Marry!

(Popillia Japonica), the "Japanese Beetle," as it is known in the United States, is native to Japan where it is are called Mamekogane and commonly referred to as Koganemushi which means "gold beetle". In the United States and Canada the Japanese Beetle is an invasive species. It is among the most destructive pests to ornamental, fruit and vegetable plants in its adult form. In its larval form it is one of the most destructive pest to and turf and pasture grasses to the eastern half of the continental United States and Canada.


Adult Japanese Beetles are about the size of a fingernail with metallic copper-green wing covers. A row of white tufts of hair project from under the wing covers on each side of the body. The adults emerge from pupation from late June to early July and begin to feed on the foliage of a disturbingly wide variety of plants from four to six weeks.

The University of Kentucky has an excellent table of plant species that are susceptible to damage by the Japanese Beetles and grubs.

The Beetles are excellent flyers and can detect edible crops and sexual pheromones of other beetles from considerable distances. These abilities make the beetles capable of congregating in alarming numbers upon a given crop where they skeletonize the leaves and damage the flowers and fruits of the plants.

Upon finding a suitable crop and/or and existing population, the beetles will cluster; mating as they eat. In the evening the female beetles retire to grass or pasture to deposit eggs two to four inches beneath the soil.

The larval stage of the Japanese Beetle are white C-shaped grub which feed upon the roots of grasses. The grubs can be distinguished from other similar grubs by a light brown exoskeleton of a head and three pairs of arms.

The grubs eat until the soil cools below 50F degrees. They then burrow below the frost line and are dormant for the winter.

Once the soil thaws in the spring the beetle resumes feeding on the roots of grass roots. They will eat until the summer where they will pupate and emerge as adults.

The grubs are among the most damaging pests to turf grass in the northeastern quarter of the United States. Heavily infested lawns and pastures can be completely destroyed.


The Japanese beetle was first discovered in the United States near Riverton, New Jersey at the nursery of Henry A. Dreer, Inc. The beetles were likely imported as grubs in iris roots which the nursery had imported from Japan five or six years before. By 1918 the insect had been identified the beetle's potential for damage to agriculture and efforts were undertaken to quarantine it by The United States Department of Agriculture, The state of New Jersey, and Federal Bureau of Entomology.

This plan proposed to limit the spread of the beetle by spraying, with arsenate of lead, a half mile-wide band of non-economic foliage around the heavily infested area, leaving patches of unsprayed grassland for egg deposition. These grassland areas were to be saturated with sodium cyanide in water to kill the immature stages. Twelve light trap stations each of 400 candlepower were to be used to attract beetles to pans of kerosene. All food plants of the beetle were to be dusted with powdered arsenate of lead in a suitable carrier. The beetles were also to be hand-picked and killed. Clean cultivation of farm lands was advocated and infested sod land was to be treated with carbon bi-sulphide. All green sweet corn in the area was to be removed under quarantine regulations.

By 1921 the quarantine had failed. Funding had been inadequate to keep the quarantine area sprayed and the beetles proved that they were able to fly outside of the quarantined area to feed on unsprayed foliage. By the end of the failed quarantine the beetle had infested 213 square miles of New Jersey and had entered Pennsylvania.

The adult Japanese Beetle was found to be destructive to over 200 food plants, including practically all the economic crops grown in New Jersey. The grubs began to become a serious pest to lawns, golf courses, and pastures. Some pastures had as many as 700 grubs in a square yard.

By 1924 the infested area grew to over 500 square miles. A carbon bi-sulphide emulsion was found effective in killing the grubs as was a process of coating foliage with an arsenate of lead in an insoluble soap such as lead oleate to kill the adults. Nine hundred thousand packages of farm products were treated in this manner and certified for shipment to points outside the quarantine area. Other treatment methods included the development of traps using a mixture of geraniol, eugenol, bran, molasses, and glycerin for bait. Carbon bisulphide vapor was used as a fumigant to treat produce. Natural parasites from Japan were released.

By the 1930's, farmland scouting and trapping activities were discontinued. Paradichlorobenzene, carbon bi-sulphide, arsenate of lead, and steam were in use as soil treatments. Fumigation of refrigerator cars and trucks with methyl bromide had replaced the manual inspection of white potatoes, peppers, blueberries, and apples. Nursery stock was being treated with an ethylene dichloride emulsion.

Once the entire state of New Jersey had been infested and the Japanese Beetle had spread far into adjoining states the state quarantine was lifted. A Federal Japanese Beetle Quarantine was put in place designed to retard the artificial spread of the insect.

Today the Japanese Beetle continues to spread naturally across the eastern half of the continental United States. This map shows the extent of widespread Japanese Beetle infestation. The beetle also has been discovered in other areas far outside of its year-to-year range of flight, suggesting that the continued practices of the federal quarantine are less than totally effective.


The federal quarantine includes the inspection, treatment and certification of millions of items including farm, nursery, and greenhouse products, and even soil, moss and sand.

Agricultural products and nursery stock may be certified in various ways, such as by freeing the roots from soil, growing the plants in certified areas which have been chemically treated, fumigation with gaseous insecticides, treatment with liquid insecticides, and using an insecticide with potting soil. Cyanide, methyl bromide, ethylene dibromide, ethylene dichloride, carbon disulphide, chloropicrin, arsenate of lead, and DDT are used in the certification work. Farm products are given certification after approved methods of grading and packing have been met, after fumigation or after manual examination, depending upon beetle conditions.

For the casual gardener and home owner who do not have access to controlled agricultural compounds, the ascribed methods for controlling the Japanese Beetle can be maddeningly ineffective.

A common method ascribed is to knock off the beetles in the early morning into soapy water. This is impractical unless the amounts of affected plants are small because of the quantities in which the beetles congregate. I have given my pole bean trellis a shake and emitted swarms of beetles some of which I find in my clothes hours later. They also have a talent for rolling off of the plant to the ground or flying away (only to return shortly.)

Chemical sprays such as Sevin and Danitol are effective in killing the beetles but they also kill pollinating bees and beneficial predators as well. For organic growers, insecticidal soaps and pyrethrins provide some benefit, but they are not highly effective. They also kill indiscriminately.

Chemical traps will only increase the number of Japanese Beetles in the vicinity. As the entomologists in New Jersey discovered, Japanese Beetles are good flyers and will swarm to both the scents of palatable foliage and to the sex pheromones of other groups of beetles. This makes the use of commercial beetle traps a very bad idea indeed.

One of the commonly ascribed methods to control the beetles is to inoculate the soil with nematodes which attack and devour the grubs in the soil from within. While effective in combating heavy infestations of grubs, it is less effective in controlling populations of adult beetles as it requires the application of nematodes over a very large area to be effective. It is also an expensive option and must be repeated over several years.

I have had success in controlling Japanese Beetles with Neem Oil. Neem Oil is extracted from the seeds of the Neem Tree (Azadirachta indica), which is a semi-tropical tree native to the Indian sub-continent. The active compound in Neem Oil is a potassium salt of fatty acids.

When sprayed upon plant tissues, that plant will absorb the active compound which is harmful to any insect which then consumes the treated plants, disrupting their reproductive and digestive systems on the hormonal level. How these compounds in Neem Oil work is still a matter of speculation in the scientific community. I have read conflicting conclusions and will decline to reference them in favor of my own observations which you may find in the following write-up.