Do Japanese Beetles Have Any Natural Predators

Japanese beetles Popillia japonica has a copper colour back, metallic blue-green head and tan wings. They also have small white hairs covering both sides of their abdomen. Japanese beetles lay eggs, which develop into small white grubs that have six legs and brown heads.

The white grub will stay underground for ten months and come out as an adult beetle and start feeding on plants the following June. Although their life cycle is only about 40 days, they can cause a lot of damage because they feed in groups.

Japanese beetles eat a wide range of crops and flowers, but they usually attack beans, raspberries, rose bushes and grapes. The most common signs of a Japanese beetle infestation include skeletonized flowers and leaves as well as brown patches in your lawn.

The beetles can damage grass because they eat the roots of garden plants and turf grasses during the spring and fall. Their feeding sessions can result in brown patches of dying or dead grass in your lawn, which can be pulled up easily due to the weakened roots.

Some birds eat both the grubs and adult Japanese beetles, so you should attract them to your garden with feeders, nesting boxes and birdbaths when you have a beetle problem.

Starlings are natural predators of Japanese beetles, so do not chase them away when you see them. Other bird predators include:

The Spring Tiphia wasp is another natural predator of Japanese beetles. The female wasp lays eggs right on the grub, eliminating up to 85% of the larvae in a garden. Consider planting firethorn, forsythia, and peonies in your garden to attract these wasps.

Other natural predators of Japanese beetles include:

The Tachinid fly is also a predator of Japanese beetles. It parasitizes the Japanese beetle by attaching its eggs to the body of the beetle. The maggots or fly larvae hatch within a day and move inside the body of the beetle to feed.

Japanese beetles have a lot of natural predators. Researchers are also looking for ways to use these predators to control Japanese beetles instead of harsh chemicals and insecticides.

This method, however, faces a lot of obstacles as the predators cannot eliminate the beetles immediately. So, the best way to deal with Japanese beetles is to keep your lawn healthy. You can do this by removing poorly nourished and diseased trees and fruits that can attract the beetles.

Hand-picking them off your plants is time-consuming, but it is the best way to get rid of these beetles. After picking them off, drop them in a bucket or jar of soapy water to drown them. You should do this in the early morning when they are less alert.

Cover your plants during the beetle’s six to eight-week feeding period. The row cover will keep the beetles out, but it will also keep pollinators out. So, do not forget to remove the covers if your plants should be pollinated.

Sprays that contain potassium bicarbonate and neem oil are effective against Japanese beetles. Neem oil contains a chemical that kills larvae, preventing them from becoming adults. However, you should not apply neem oil near ponds, lakes, and rivers because it can be harmful to aquatic life. 

If you are dealing with many Japanese beetle grub, you should consider using Japanese beetle traps. Geraniol and eugenol are attractive to Japanese beetles and other insects, so you might attract more beetles to your yard as well. However, the traps do not effectively subdue adult Japanese beetles. If you still want to proceed, make sure to place the trap far away from your plants. That way, the beetles will not land on your favourite crops and flowers.

You can also use fruit cocktail traps. Open the fruit cocktail can and place it under the sun for one week to ferment. After a week, place the can on top of wood blocks or bricks in a pail filled with water. Put the pail approximately 25' from the plants that you wish to protect from the beetles. They will drown when they fall into the pail filled with water.

Traps that we recommend are the Japanese Beetle Trap, Green Earth Japanese Beetle Trap, and Safers Japanese Beetle Trap. When choosing the Safers brand, we recommend that you also get the Safers Japanese Beetle 1 Refill Bait and the Safers Japanese Beetle 3 Refill Bags. See recommended products below:

You can use insecticides to deal with Japanese beetles, but make sure to ask the local garden center or cooperative extension about the insecticides that are allowed in your area. Another option is to make a homemade spray by mixing vegetable oil (one cup), rubbing alcohol (one cup), dishwashing detergent (one teaspoon) and water (one quart) together.

Transfer the solution into a spray bottle. Since homemade sprays pose a risk of damaging plant leaves, you should use them sparingly. Test a bit of the solution on a small portion of the plant and leave it there for 24 hours. If there is no adverse reaction, you should spray the rest of your plant with the solution. Apply the solution in the morning. If the plant starts to wilt, you should rinse it immediately with water.

Other insecticides that we recommend for dealing with adult Japanese beetles and their grubs are Botanical Green House Vegetables BUG KILLER 950ml, Botanical Plant & Flower Liq Insect Killer 950ml and POT-It Plant Multi Insect RESIDUAL 400gr.

You can plant geraniums in your garden to save your precious plants from Japanese beetles. They get dizzy when they eat the flowers. When they fall off the plants, you can dispose of them easily with a brush and dustpan.

Beneficial nematodes can kill the white grubs that develop into adult Japanese beetles. You should apply these nematodes in spring before the pests emerge. You should also apply milky spore to kill grubs. It can take a year to get established in the soil, but it will keep working for ten years.