Japanese Beetle History

The Japanese Beetle is an invasive pest to the United States. It  is originally from Japan, where it is not considered a serious pest because of the presence of natural predators and pathogens that naturally control the Japanese Beetle population. This beetle was first discovered in the United States in 1916 in New Jersey and has since spread through the North American continent. It is considered a very serious pest of turf, but it can also damage a wide variety of hosts, affecting both agricultural and ornamental crops.

Japanese Beetle Hosts

One of the reasons why Japanese Beetles are so prolific and widespread in the united states is its wide variety of suitable host plants. Adult Japanese beetles feed on leaves and flowers. Hosts may include fruit and nut trees, small fruit bushes, ornamental shrubs and flowers, garden crops and vine crops. Grape, Apple, Cherry, Peach, Plum, Rose and Corn seem to be preferred hosts for adult feeding. Damage from adult feeding can include skeletonizing leaves, reduced crop through feeding of flowers, or in the case of corn through feeding on the silk which stunts kernel formation. Turf is damaged by the larvae, which can cause large patches of dead grass.

Japanese Beetle Identification

Japanese Beetles are not difficult to identify for experienced insect scouts. Adult beetles are oval-shaped and can be up to 0.5 inches (13 mm) longs, and about 0.25 inches (6 mm) wide. The body is distinguished by the bright, metallic looking, green color. Legs are darker green and wing covers are brown. White tufts of hair can be observed just behind the the wing covers along the sides. Eggs are small, white and oval and are laid in the soil. The Larvae are white and c-shaped with 3 pairs of legs, and can grow up to 1 inch (25 mm). Pupae become light reddish brown.

Japanese Beetle Life Cycle

Japanses beetle females lay eggs in small clusters just below the soil of the surface. Each female can lay up to 60 eggs in a lifetime. Eggs usually take between 10 and 14 days to hatch, after which larvae emerge. Japanese Beetle larvae can feed on the roots of many types of plants, but prefer grass if it is available. As they feed, the larvae move into the soil before overwintering. In spring larvae become active again and resume feeding on roots. There are three instars of larvae that Japanese Beetles develop through before pupating.

Pupation occurs later in spring and adults emerge from 8 to 20 days later. After adults emerge, they feed on foliages, flowers and fruit before mating. In most cases, Japanese Beetles have one generation per year.

Researchers have developed a growing degree day model, available on the Pest Prophet app, which can be used to predict adult Japanese Beetle emergence based on weather data. This can be a very useful tool for determining when to begin adult beetle scouting. Learn more about using the Japanese Beetle Growing Degree Day model.

Observation and Surveying methods

Adult Japanese Beetles

In order to properly execute an integrated pest management program for Japanese Beetles, you must first observe and survey the field or property to determine the insect presence and amount. Adult beetles can be observed through trapping. Traps use chemical lures, pheromones or floral smells, to attract adult beetles to the trap where they are caught. These traps can be used to approximate the beetle population in a given area. If the trap is filled after 1 day, it is a severe infestation. If only a few beetles are caught after a week, the infestation is not severe. However, adult beetles may fly from several hundred yards away, so adult beetle traps cannot be used to definitely assess the amount of beetle larvae present in an exact location.

Larvae

To survey for larvae, samples need to be dug  up from the soil and assessed for larvae. A square hole, 8 by 8 inches and 3 inches deep is recommended. The sod should be turned over, and the area underneath assessed for larvae. If done carefully and watered immediately, it usually possible to put the patch of turf back without it dying. Areas of damage in the previous season should be targeted with soil surveys first. Beyond this, a random sampling method should be used through the field. Using this method, you might be able to observe areas with more larvae present, or “hot-spots’, which can be used to target treatments. Larvae per square foot can be calculate from these 8 in by 8 in samples by multiplying by 2.25. If there are more than 10 larvae per square foot, treatment should be considered. In some cases, an even smaller threshold of larvae may be used for treatment decisions.

Japanese Beetle Control Methods

There are several different approaches that can be used to control Japanese Beetle populations. Chemical, biological, or mechanical control methods may be considered for use on Japanese Beetles. Any control method should be used as part of an integrated pest management program, along with careful scouting, field sanitation and planning.

Chemical Control Of Japanese Beetles

In cases of severe Japanese Beetle infestation, chemical control methods may be needed to decrease population. With any pesticides, there is a risk to people and wildlife if improperly used and when pesticides are properly used, there may also be unintended consequences such as disrupting natural predator populations. When using any pesticide, the label should always be read entirely and all instructions should be followed carefully. Timing of the pesticide application is also very important to how effective it will be.

Chemical control options for adult Japanese Beetles include (active ingredients): Bifenthrin, Carbaryl, Cyfluthrin, Deltamethrin, and Permethrin. For larvae the following may be considered: Imidacloprid, Halofenzide, Thrichlorfon, Chlorantraniliprole. Always check the label for specific location and crop regulations, as these chemicals may not always be suitable for use. There are chemicals that may be considered for Japanese Beetles. Local Cooperative Extension services can help decide which is best for a given location and situation.

Biological Control of Japanese Beetles

There are several biological control options available for Japanese Beetles, such as using parasites, nematodes, or fungi that can target Japanese Beetles. Generally speaking, using biological control options will usually not have as much immediate effect as chemical control, but if done properly and allowed to establish, can provide longer lasting control. There is also less risk of adversely affecting beneficial insect populations.

Nematodes

Nematodes are microscopic parasitic roundworms. Some nematodes feed on insects and can be used for biological control. These nematodes are able to feed on larvae and once they penetrate the larvae, they can inoculate the grub with a symbiotic bacteria that reproduces and kills the larvae. The nematode then feeds on the bacteria as it progresses through its life cycle, eventually killing the larvae. The two nematodes that are work best for biological control of Japanese Beetles are Steinernema glaseri and Heterohabditis bacteriophora, which is commercially available.

The key to having success with beneficial nematodes, and all biological controls, is to keep in mind that they are living organisms and will require a specific environment to survive long enough to control the target pest. Nematodes have a high oxygen requirement, so they will work better in some soils. THey can usually be applied by standard insecticide application equipment, but must be applied quickly after mixing with water.

Bacteria

Bacillus thuringiensis (Bt) is a bacteria that is commonly used as an insecticide on a wide variety of insects. It is a bacteria that must be ingested by the insect before poisoning it. There is a strain of Bt that is registered for use of Japanese Beetle larvae. It can be applied to soils in a similar manner to insecticides.

Bacillus popillae, also known as Milky Spore, is a bacterium that is registered for Japanese Beetle larvae control. These spores reproduce in the larvae’s gut and enter the blood, killing the larvae. When the larvae is killed it releases spores back into the soil which are able to infect other larvae. Through this process, Milky Spore population can build up in soil over a few years, and once the population is successfully established, can control Japanese Beetle very effectively.

Parasites

Parasites are another biological control method that may be considered for Japanese Beetle control. Two different parasites of Japanese Beetles have been introduced in the United States from Asia: Tiphia vernalis, which is a parasite of Japanese Beetle larvae, and Istocheta aldrichi, which is a parasite of the adult Japanese Beetle. Both have been successful in some areas at repressing Japanese Beetle populations, however neither are currently commercial available. To make use of these parasites, they must first be established in a area, then they may be attracted to a field and assisted in its survival to maximize parasitism of Japanese Beetles.

Tiphia vernalis is a small parasitic wasp that lays eggs in Japanese Beetle larvae. Once the egg hatch, the larvae feed on the Beetle grub, killing it. They have populations established throughout the Northeastern United States and in North and South Carolina. Adult wasps feed almost exclusively on honeydew of aphids on maple, cherry and elm trees as well as peonies. Nectar from tulip poplars have also been shown to be a food source for adult wasps. Planting these plants can help increase the likelihood of wasp establishment and parasitism in a given field.

Winsome Fly (Istocheta aldrichi) is a fly that can parasitize adult Japanese Beetles. Female flies lay eggs on the thorax of female Japanese Beetles and can lay up to 100 eggs in a two week period. Once the eggs hatch, the maggots feed on the Beetles, boring into the body and killing it. It is able to suppress populations quickly by killing beetles before they can reproduce. Istocheta aldrichi commonly feeds on aphid nectar deposited on Japanese knotweed.

Cultural Practices

Another important factor in preventing Japanese beetles is to keep trees and plants healthy and watered. Diseased, and water or nutrient deficient plants are more susceptible to damage from Japanese Beetles. Overripe, rotten or diseased fruits are also attractive to Japanese Beetles, and the odor from these fruits can bring Japanese Beetles from neighboring fields. Damaged areas in turfgrass are attractive to female Japanese Beetle for egg-laying.

There are also many plants that are resistant to Japanese Beetle damage. These plants can be used to reduce the potential for large Japanese Beetle outbreaks. When planting ornamental plants, there should be a mix of susceptible with non-susceptible plants to reduce the amount of Japanese Beetle damage.

Mechanical Traps

Another non-chemical control option for Japanese Beetles is mechanical traps. While usually not 100% effective at killing beetles, mechanical traps can greatly reduce beetle populations and reduce egg-laying. One thing to consider is that because traps often can attract more beetles than they can capture, they should not be placed near susceptible plants. Traps should be placed around the borders of a property, away from plants that could be damaged. Optimal trap placement should coincide with emergence of adult Japanese Beetles, which usually occurs in summer. The Pest Prophet app can be used to approximate when adult emergence will occur, based on the weather data of a given area.

Any of these techniques may be used in combination with each other to best prevent Japanese Beetle damage and infestation.

Sources:

https://www.cdfa.ca.gov/plant/pdep/target_pest_disease_profiles/japanese_beetle_profile.html

https://www.aphis.usda.gov/plant_health/plant_pest_info/jb/downloads/JBhandbook.pdf