What is the natural enemy of the Japanese beetle?

The Japanese beetle (Popillia japonica) is an invasive insect pest that has become established in many parts of North America. Originally from Japan, these metallic green and bronze beetles were first discovered in the United States in 1916 in New Jersey. Since then, they have spread to many states east of the Mississippi River, where they feed on over 300 species of ornamental and agricultural plants. Japanese beetles are a serious pest that can quickly defoliate plants, leaving them weakened and vulnerable. Understanding the natural predators and parasites that help keep Japanese beetle populations in check in their native range can help guide biological control efforts in invaded regions.

What eats Japanese beetles?

In their native Japan, Japanese beetles are kept in check by a number of natural enemies. Some of the most important natural predators and parasites of Japanese beetles include:

Parasitic wasps

Several species of tiny wasps lay their eggs inside Japanese beetle grubs living underground. The wasp larvae hatch and consume the beetle grubs from the inside out, killing them. Some of the most common parasitic wasps that attack Japanese beetles include:

– Tiphia vernalis
– Tiphia popilliavora
– Istocheta aldrichi
– Oomyzus sokolowskii

These wasps can parasitize up to 75% of grubs in heavily infested areas in Japan, playing a major role in biological control. Releasing these parasitic wasps at invaded sites in North America may help reduce Japanese beetle numbers.

Predatory beetles

Certain ground beetles will feed on Japanese beetle grubs in the soil. Two predatory beetles that have proven effective at reducing Japanese beetle numbers in Asia are:

– Anomala testaceipennis
– Blitopertha orientalis

These beetles populate the soil and hunt for grubs, piercing their tough outer shells with powerful mandibles. Each predatory beetle can consume up to 60 beetle grubs in its lifetime. Releasing large numbers may significantly cut down Japanese beetle populations by attacking them underground.

Predatory flies

Several flies are natural enemies of the Japanese beetle. These include:

– Istocheta aldrichi – These flies lay eggs near beetle grubs in the soil. When the eggs hatch, the fly larvae burrow into the grubs and devour them.
– Sarcophagid flies – These flesh flies lay eggs in soil. The larvae attack and consume nearby beetle grubs.
– Tachinid flies – Parasitic tachinid flies lay eggs on the back of adult beetles. When the eggs hatch, the larvae bore into the adult beetles’ bodies and kill them.

Using releases of these predatory flies may help reduce damage from Japanese beetles in two ways – by attacking both the grubs in the soil and the mature beetles feeding above ground.

Entomopathogenic fungi

Certain soil-dwelling fungi are lethal to Japanese beetle grubs. Species like Metarhizium anisopliae and Beauveria brongniartii infect and kill the grubs while they are feeding underground. Applying spores of these fungi to lawns and gardens has been shown to reduce Japanese beetle numbers in Asia. This microbial insecticide approach holds great potential as a biocontrol treatment.

Entomopathogenic nematodes

Some roundworms in the soil can act as parasites of Japanese beetle grubs. The nematodes Heterorhabditis bacteriophora and Steinernema glaseri enter grubs through natural openings and release symbiotic bacteria that kill the beetle larvae. Applying parks with these nematodes to lawns can cut down grub populations. The nematodes persist in the soil and provide ongoing control.

Birds, raccoons and other vertebrates

Many birds, mammals and reptiles opportunistically prey on adult Japanese beetles. These include:

– Crows
– Starlings
– Skunks
– Raccoons
– Opossums
– Garter snakes
– Mice

While they may eat some beetles, they do not provide effective pest control. But avoiding use of pesticides will allow these generalist predators to continue attacking Japanese beetles and other pests.

Table: Key natural enemies of Japanese beetles

How can natural enemies be used for biocontrol of Japanese beetles?

Researchers and land managers are working to weaponize these natural enemies as biocontrol agents to combat destructive Japanese beetle infestations. Some approaches include:

Conservation of native predators

Avoiding broad-spectrum insecticide use allows native and introduced predators and parasites to persist and continue attacking beetles in the area. Pesticides harm these beneficial species that keep beetles in check in their native range.

Classical biological control

This involves deliberately importing natural enemies from the pest’s native range and releasing them at invaded areas lacking these predators. Parasitic wasps, predatory beetles and flies have been introduced from Japan to the US to control Japanese beetles with some success.

Augmentative biological control

This relies on mass-rearing natural enemies in laboratories and repeatedly releasing them at infested sites. Fungal spores, nematodes and predatory insects can be produced this way. Regular releases boost biocontrol agent numbers to suppress beetles.

Habitat management

Creating suitable habitats encourages native and introduced biological control agents. Features like beetle banks, cover crops and flowering plants provide resources that enhance biocontrol populations.

Conclusion

A suite of natural enemies including wasps, flies, beetles, fungi and nematodes play an important role in controlling Japanese beetle numbers in their native range. By studying these interactions, researchers hope to identify the most promising biological control options to suppress invasive beetle populations. Using conservation, importation, augmentation and habitat management to employ these agents can lead to sustainable, ecological pest management. While biocontrol has already had some successes against Japanese beetles, further research and integration with other IPM tactics will provide the greatest impact.