Japanese Beetle

Plants that Japanese Beetles DON'T like

Japanese beetle is usually spread to new locations as eggs or grubs in soil surrounding nursery plants. Adult Japanese beetles are often found around airports, presumably transported by cargo planes. Since its introduction, despite quarantines, Japanese beetle has spread to most, if not all, states east of the Mississippi River and into parts of Minnesota, Iowa, Missouri, Nebraska, Kansas, Arkansas and Oklahoma. There are two known pockets of infestation in Colorado, one near Denver and the other in Palisade area on the West Slope, suggesting that the Rocky Mountains are not an insurmountable barrier. Studies predict that Japanese beetle will become established in all states bordering the Gulf of Mexico.

There are a number of control strategies that can reduce beetle populations and feeding, and there is lots of information available on the internet (see for example the following USDA site: http://www.aphis.usda.gov/plant_health/plant_pest_info/jb/index.shtml) and through county agricultural agents and garden shops. Most control recommendations rely on long-term, multifaceted approaches focusing on combinations of chemical, cultural, and biological practices. There is no simple (and effective) one-shot approach.

More knowledge is better than less, and any control strategy should be based on the dynamics of the beetle's life cycle. In the Northeast in June, adults emerge from the soil, where they have overwintered as grubs. They then feed, mate, and lay eggs until a killing frost. The peak of adult beetle numbers is July and August. Eggs are laid in the soil after a few weeks of feeding and mating. A female can lay 40 to 60 eggs during her life. Eggs hatch in July and the resulting grubs feed on the roots of grasses, sometimes causing dead patches in a lawn. Grubs are fully grown by the end of August. Older grubs are quite tolerant to drought and high moisture.

When the soil cools to about 60°F in the fall, grubs move deeper underground, and most overwinter at 2 to 6 inches below the surface. When soil temperature rises above 50°F in the spring, grubs begin to move up into the root zone, feed for 4 to 6 weeks, and undergo pupation (the transformation from grub to adult). Adults emerge and the cycle repeats itself.

There are a number of synthetic insecticides that target different points in the beetle's life cycle. There are also "biorational" insecticides derived from plants or other natural sources that have modes of action different from conventional insecticides; these are considered to have lower risks to humans, wildlife and the environment. Conventional and biorational insecticides have a place in a control strategy. Consult local county agricultural agents and garden stores for recommendations.

Among the cultural practices that are utilized to reduce beetle populations are habitat manipulation and trapping. Japanese beetle feeds on almost 300 plant species, but it will feed on some plants only moderately or not at all. The composition of plants in a lot or garden can thus have a significant influence on the attractiveness of a property to Japanese beetles. This may be cold comfort to those in highly infested areas with mature landscaping, but beetle plant preference should be considered when replacing woody plants and in what herbaceous ones are grown.

Traps are commonly sold in hardware stores and garden shops. They are baited with beetle pheromone or floral scent. They are remarkably effective in attracting beetles. Observing the beetles at traps, it's easy to see that the beetles are not very good flyers. Beetles bounce off the sides of the trap, overshoot it, or simply congregate on its side, mating, sunning, or clambering over each other. For every four beetles that a trap attracts, only three are captured. My belief is that traps attract more beetles to a property than had one not been used; the net effect is more beetle damage. Traps should never be placed near plants that beetles favor.

In its native habitat in Asia, Japanese beetle is not as destructive as it is here. A long-term control strategy that makes good sense is determining and promoting Japanese beetle parasites and pathogens. USDA has introduced several exotic insect parasites of Japanese beetle. These have shown varying degrees of success. There are also nematodes and bacterial pathogens that are effective in checking beetle populations and that are relatively easy for gardeners and homeowners to use.

USDA entomologists imported (1920s and early 1930s) an Asian wasp called spring tiphia (Tiphia vernalis) that is parasitic to Japanese beetle. These wasps attack beetle grubs. In the spring after mating, the female burrows into the soil looking for grubs. When she finds one, she attaches an egg to it. The egg hatches and the larva feeds on and eventually kills the grub. The wasp larva overwinters in the soil in a cocoon from which it emerges in spring to start the cycle over. Spring tiphia were released in Connecticut between 1936 and 1949. Recent surveys show that the wasp is present in every Connecticut county and is attacking Japanese beetle grubs.

Another parasitic insect imported from Asia by USDA is Istocheta aldrichi, a tachinid fly. In North America, tachinid flies are an important group of insect parasites. In Asia, Istocheta aldrichi specifically parasitizes adult Japanese beetles. The fly attaches its eggs to the thorax of the beetle, and the larva hatches within 24 hours, bores into the beetle, and begins to feed.

This fly was introduced to New England at about the same time (1922) as spring tiphia. It is established in much of New England and is found on 20% or more of Japanese beetles tested. In Japan, I. aldrichi is the primary biological control agent for Japanese beetle, but in New England, it is not well synchronized with the beetle's life cycle and tends to emerge earlier than the beetle. In more northern areas (Maine, for example), where I. aldrichi emerge later, synchronization appears to be better. The fly may thus be a good candidate for introduction in the North Central states.

Active research is continuing with both of these insects, and efforts are being made to establish the fly in new areas. To my knowledge, there are no commercial sources of either. But these are living insects with distinct needs and requirements. It's probably most efficient for an agency such as the USDA to release and establish them on a community-wide basis.

Several nematodes (microscopic parasitic roundworms) are effective against Japanese beetle larvae. These nematodes burrow into the grub and proceed with their life cycle, reproducing and ultimately killing their host (the grub), at which time more nematodes are released into the soil. For maximum effectiveness, nematodes are applied when the grubs are small (about 2 weeks after the beetles appear, late June to early July in the Midwest) but can be applied until frost. The two nematode species that are most effective against grubs are Heterorhabditis bacteriophora and Steinernema glaseri. The nematodes do not persist well in the soil, however. Preparations of live nematodes of both species are available commercially and easily applied with a watering can or a garden-hose spray apparatus.

Bacillus thuringiensis (Bt) is a naturally occurring soil bacterium that produces an insecticidal protein. It was made famous in the 1990s when the gene for the insecticidal protein was genetically engineered into corn and cotton. There are many strains of this bacterium that are pathogenic to specific insects. There is no specific Japanese beetle strain, but the protein from several strains is active against Japanese beetle grubs. A powered formulation applied to a lawn like a fertilizer is generally available at garden stores or through catalogs.

The most widely used and effective natural control for Japanese beetle larvae is the native North American bacterium Bacillus popilliae. It causes a disease called "Milky spore" because of the characteristic milky appearance infected grubs exhibit. The bacterium was first registered for use on Japanese beetle grubs in the USA in 1948. When grubs ingest the bacterial spores, they become infected and die and as many as 2 billion new spores are released into the soil. The bacterium, and hence grub-disease potential, builds up in soil over time (2-4 years). Milky spore disease is effective in suppressing beetle populations. This too is widely available and is spread as a powder on lawns.

The short story is that Japanese beetle is here to stay; sooner or later, it will probably infest all 50 states and much of Canada. We must adapt to it. USDA and other agencies continue to explore control strategies. For the gardener or homeowner, the most effective strategy will be long term and rely on combinations of chemical, cultural, and biological practices.

Taken from "Meet the Beetles: Frederick Dobbs on Japanese Beetles," Heronswood Voice, Heronswood Nursery.

Avoiding Japanese Beetles

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