When used improperly, insecticides can pose serious hazards to people, wildlife, and the environment. There is also increasing concern about the fate of insecticides in the environment and the potential for pesticide runoff to cause water contamination. Because of these concerns, scientists believe that biological control agents are preferable to pesticides in the suppression of turf insects.
Homeowners who choose biological methods to control Japanese beetle populations can successfully use parasites, nematodes, fungi, or other biologically based approaches. Some of these agents are commercially available to homeowners; others are not. While they take a little longer to produce the same results as insecticides, biological control agents last longer in the environment. More importantly, they do not adversely affect nontarget or potentially beneficial organisms.
Nematodes: Insect-eating nematodes - microscopic parasitic roundworms - actively seek out grubs in the soil. These nematodes have a mutualistic symbiotic relationship with a single species of bacteria. Upon penetrating a grub, the nematode inoculates the grub with the bacteria. The bacteria reproduce quickly, feeding on the grub tissue. The nematode then feeds on this bacteria and progresses through its own life cycle, reproducing and ultimately killing the grub.
The two nematodes that are most effective against Japanese beetle grubs are Steinernema glaseri and Heterorhabditis bacteriophora. The latter is commercially available.
When using nematodes, remember they are alive and have a fairly high oxygen requirement. They are typically sold on a carrier, which they can survive on for a month or 2 under cool conditions. They can be applied with any standard insecticide applicator. Once mixed with water, nematodes must be applied fairly quickly. Follow accompanying directions carefully for best results.
Nematodes may be purchased in lawn and garden shops or through biological mail-order catalogs.
Bacillus thuringiensis (Bt): Bt is a naturally occurring soil bacterium typically used as a microbial insecticide. The Bt strain registered for the Japanese beetle is for use on the grub stage only. Bt is a stomach poison and must be ingested to be effective. Apply it to the soil as you would insecticides. Effectiveness is similar to that of insecticides. Check with your extension agent regarding the availability of Bt.
Milky Spore: Milky spore is the common name for spores of the bacterium Bacillus popillae. This bacterium was first registered for use on turf in suppression of the Japanese beetle grub in the United States in 1948.
Upon ingestion, these spores germinate in the grub's gut, infect the gut cells, and enter the blood, where they multiply. The buildup of the spores in the blood causes the grub to take on a characteristic milky appearance.
Milky spore disease builds up in turf slowly (over 2-4 years) as grubs ingest the spores, become infected, and die, each releasing 1-2 billion spores back into the soil. Milky spore disease can suppress the development of large beetle populations. But it works best when applied in community-wide treatment programs. Check with your extension agent regarding the availability of milky spore material.
Parasites: Releasing natural enemies or parasites of an exotic insect is a successfully proven method to reduce pest populations. Introduced parasites must be shown to be host specific (that is, to parasitize only the target pest) before USDA approves releasing them. Two such parasites of the Japanese beetle have been brought to the United States from Asia. Researchers have successfully established these insects in areas inhabited by the Japanese beetle, and the parasites are now functioning as important biological control agents of the beetle.
Tiphia vernalis, a parasite of the Japanese beetle grub, and Istocheta aldrichi, a parasite of the adult, have been shown to be important in regulating the population dynamics of the beetle in the Northeastern United States.
These parasites are not yet commercially available; however, you can contact your local extension agent to see if they are established in your area. If they are, planting the appropriate food plants will attract these parasites and increase the rates of parasitization, and thus help control the Japanese beetle on your property.
Tiphia vernalis - This small, parasitic wasp of Japanese beetle grubs resembles a large, black, winged ant. Its current distribution is believed to be throughout the Northeastern United States and south to North Carolina.
After a brief period of feeding and mating during the spring, the female wasp digs into the soil, paralyzes a beetle grub by stinging, and then deposits an egg on the grub. When the egg hatches, the emerging wasp larva consumes the grub.
Food sources: Adult wasps of this species feed almost exclusively on the honeydew of aphids associated with the leaves of maple, cherry, and elm trees and peonies. In North Carolina, the nectar of tulip poplars has been found to be an important food source for the adult wasps.
Istocheta aldrichi - This solitary fly is an internal parasite of the adult Japanese beetle. The female flies are capable of depositing up to 100 eggs during a period of about 2 weeks. The eggs are usually laid on the thorax of the female beetles. Upon hatching, the maggot bores directly into the beetle's body cavity, killing the beetle.
Because it does not take this fly long to kill the beetle, I. aldrichi can suppress Japanese beetle populations before beetles can reproduce.
Food sources: I. aldrichi is commonly seen feeding on aphid nectar deposited on Japanese knotweed (Polygonum cuspidatum), a persistent perennial weed native to Japan.
Habitat Manipulation: Sometimes people can suppress the population of pest insects by making the habitat less suitable for them. Cultural methods typically employed in the control of the Japanese beetle include planting resistant plant species and using mechanical traps designed to attract and trap the adult beetles.
Diseased and poorly nourished trees and plants are especially susceptible to attack by beetles. Therefore, keep your trees and plants healthy. Also, prematurely ripening or diseased fruit is very attractive to beetles. Remove this fruit from the trees and the ground. The odor of such fruit will attract beetles, which are then in a position to attack sound fruit.
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. Having a well-dispersed mixture that favors nonpreferred species can reduce the level of beetle-caused damage.
Susceptible and Resistant Flora
When beetles are abundant, damage to plants can be minimized by using species that are immune to or seldom attacked by the insect. When planting a new ornamental or modifying established plantings, make more extensive use of trees, shrubs, and other plants that are not preferred by the beetle. Select plants that are least likely to be seriously injured. Use the following list as a guide for determining what plants to cultivate on your property, and what plants to stay away from.
Keeping Japanese Beetle at Bay: Best and Worst Plants to Have in Your Yard
|Plants Resistant to
Adult Japanese Beetle Feeding
|Plants Susceptible to
Adult Japanese Beetle Feeding
|| Magnolia sp.
||1. American linden
|| Tilia americana
|| Cercis sp.
|| Malus sp.
|| Cornus sp.
|| Malus sp.
|4. Red maple
|| Acer rubrum
||4. Japanese maple
|| Acer palmatum
|5. Northern red oak
|| Quercus rubrum
||5. Norway maple
|| Acer platanoides
|6. Burning bush
|| Euonymus alatus
|| Rosa sp.
|| Ilex sp.
||7. Crape myrtle
|| Lagerstroemia sp.
|| Buxus sp.
||8. Pin oak
|| Quercus palustris
|| Tsuga sp.
||10. Plum, Apricot,
|1. False cypress
||1. Black walnut
||9. Virginia creeper
Courtesy of the USDA