The Japanese beetle is a beautiful flying insect with an iridescent green head and thorax and copper colored wings.
It’s a rather clumsy flyer and also quite noisy; you’ll probably hear the buzz of its wings before you see it.
This insect is a native of Japan where it is kept in check by natural predators.
In North America it is a mostly uncontrolled pest that can harm rose bushes, grapes and many other plants.
What Do They Eat?
You can tell that you have an infestation of Japanese beetles by looking at the foliage of your plants. If they are skeletonized (the material between the veins of the leaves is eaten) there is a good bet that you have these unwanted guests.
The only natural enemy of the Japanese beetle in North America is the Anchor Bug, a distinctively shield-shaped insect that can be green or brown and is quite common in the areas favored by the beetles. Some locales refer to them as “stink bugs” and you should welcome them to your lawn and garden!
Female Japanese beetles begin the life cycle by eating your plants, mating then digging into the dirt of your lawn or garden to lay their eggs. They feed some more, mate again and lay more eggs. Each female can lay about 50 eggs each season.
The eggs of the Japanese beetle are small, white and oval.
As the eggs hatch and grow into larvae they work their way up to the roots of your plants like the grass of your lawn or the vegetables in your garden. When the soil begins to cool in the autumn they move deeper underground until it warms again in the spring.
The larvae appear as white grubs that get longer as they feed and grow. Then they change to pupae and begin their transformation into adult beetles.
Then they enter the pupae stage and progress to emerge in May and June as adults. This is why they are called June Bugs in some locales.
New adult start out the color of cream and become reddish brown as they age. In their final adult stage they are less than ½” long and typically live for about two months. They will eat the foliage of tomatoes, pears, peppers, roses, peaches, all berry bushes, corn, peas, and other vegetables that humans eat.
How Did They Get Here?
It’s believed that the Japanese beetle found its way to the United States sometime before 1912 when the government began inspections for bugs and other non-native pests. The first beetle was found in a nursery in New Jersey 1916 and is thought to have made the journey in a shipment of iris bulbs years at least 4 years before they were first spotted. In 1939 a Japanese beetle in Canada was found in a tourist’s car that had crossed into Nova Scotia on the ferry from Maine.
The Japanese beetle is at its most vulnerable in its larval stage, often dying from milky spore disease. In fact, the USDA developed a commercially available powder to spread milky spore disease which doesn’t affect plants but will kill the larvae.
Natural repellants are garlic, chives, tansy, catnip and the remains of its dead companions. None of these is very effective. You can spray them with soapy water and collect the bodies the next morning or knock them off plants into a jar of soapy water. They tend to feed in groups so you will often find groups of them feeding on your plants. Beetle traps attract more bugs than they actually trap so it could only increase the traffic, not the kill rate.
Look at your lawn in the early spring. Lift up a section about 1 foot square and if there are a dozen or more grubs there you may want to consider lawn treatment with grub control.
The Japanese beetle is a beautiful creature to look at but if you value your lawn and garden you’ll need to get rid of them.