Complete Guide To The Japanese Beetle
Quick Facts About Japanese Beetles
|
Scientific Name |
Popillia japonica Newman |
|
Common Name(s) |
Japanese Beetle |
|
Animal Type |
Herbivore |
|
Diet |
Foliage, fruits, and flowers of more than 400 different plants |
|
Lifespan |
1-2 years |
|
Notes |
Invasive, non-native species and major agricultural pest |
Japanese Beetle Image Gallery
How To Identify Japanese Beetles
- Adult Japanese Beetles are broadly oval, grow to 0.4 inches (1.1 cm) in length.
- Female Japanese Beetles tend to grow a little bit bigger than males, who grow to about 0.8 cm long.
- Japanese Beetles have:
- Metallic green heads, thoraxes, and abdomens
- Hardened, ridged, bronze wing covers (called “eytra”) that don’t cover the entire abdomen
- 5 tufts of short, white hairs on both sides of the abdomen and an additional pair of hair tufts on the abdominal tip.
- Japanese Beetle larvae are called “grubs”. They hatch from eggs, start out small, and grow to 1.3 inches (3.2 cm) over three separate growth periods, called “instars”.
- Japanese Beetle grubs have:
- Soft, translucent, creamy white bodies that curl into C-shapes
- Yellowish-brown heads with chewing mouthparts
- Three pairs of jointed legs
- Dark abdominal tips due to ingested soil showing through their thin, soft skin
- Japanese Beetle grubs have:
How To Find Japanese Beetles
Japanese Beetles are invasive, non-native species that were accidentally introduced into the United States in 1916. Since their first appearance in New Jersey, they’ve spread across the eastern and central United States and are major agricultural and garden pests.
In North Carolina, adult Japanese Beetles appear from June through August in large numbers. These beetles are easy to find in the wild. They feed voraciously on more than 400 species of wild and cultivated plants, feed out in the open on top of leaves, and prefer to position themselves on the highest leaves of their chosen plants and chew their way down.
Look for Japanese Beetles on the leaves of bushes and trees in sunny locations. It’s almost guaranteed that if you find one Japanese Beetle, you’ll find many others in the same area because the beetles congregate in large numbers.
Japanese Beetle grubs are easy to find if you’re willing to dig into the soil at least 8 inches (20 cm) deep. Look for Japanese Beetle grubs in soil under grass growing in sunny areas in the early spring.
What Japanese Beetles Eat
How Do Adult Japanese Beetles Eat?
Adult Japanese Beetles eat plant leaves. They start feeding on the highest leaves then work their way down. They perch on top of the leaves and chew through the soft tissue between the leaf veins at a rate of 30-40 square millimeters per hour (Capinera 2001), leaving lace-like skeletons.
Japanese Beetles congregate in huge numbers on certain plants because the plants release odors in response to the damage to their leaves that attract more and more Japanese Beetles (Resh and Carde 2009). These volatile chemicals are considered “kairomones” in this context because they hurt the “sending species” (the plants) and help the “receiving species” (the Japanese Beetles).
It’s a vicious cycle that usually kills the host plants. Plants depend on the surface area of their leaves for photosynthesis; when the Japanese Beetles skeletonize the leaves beyond a certain tipping point, the plants can’t keep themselves alive anymore.
Female Japanese Beetles tend to arrive at food plants and start feeding first, so are considered the “pioneers” that initiate feeding aggregations. Larger male Japanese Beetles arrive later in the day, likely attracted to both the food source by the kairomones and the presence of females as potential mates (Kowles and Switzer 2012, https://doi.org/10.1007/s10905-011-9291-7).
What Do Adult Japanese Beetles Eat?
Adult Japanese Beetles feed on more than 400 different plants, although they prefer only about 100 or so of these when given a choice. No other insect is known to eat as many different kinds of plants as the Japanese Beetle and this is one reason why this species is such a pest to American farmers and gardeners.
Adult Japanese Beetles feed on:
- Trees:
- Birches, like:
- River Birch (Betula nigra),
- Sweet Birch (Betula lenta),
- Paper Birch (Betula papyrifera),
- Yellow Birch (Betula alleghaniensis)
- Black Walnut (Juglans nigra)
- Crab Apple (Malus spp.)
- Elms, like:
- Winged Elm (Ulmus alata),
- American Elm (Ulmus americana),
- Slippery Elm (Ulmus rubra)
- Horse Chestnut (Aesculus hippocastanum)
- Maples, like:
- Black Maple (Acer nigrum),
- Mountain Maple (Acer spicatum),
- Norway Maple (Acer platanoides),
- Red Maple (Acer rubrum),
- Southern Sugar Maple (Acer saccarum va. saccarum)
- Sassafras (Sassafras albidum)
- Birches, like:
- Cultivated fruits:
- Apples
- Apricots
- Blueberries
- Cherries
- Grapes
- Nectarines
- Peaches
- Plums
- Raspberries
- Blackberries
- Cultivated vegetables:
- Asparagus
- Beets
- Broccoli
- Corn
- Lima Beans
- Okra
- Potato
- Rhubarb
- Snap Beans
- Poison Ivy
- Garden flowers, especially roses.
How Do Japanese Beetle Grubs Eat?
Japanese Beetles live under the soil and chew on the roots of turf grass and other plants. They burrow through the soil using their jointed legs and tough head capsules. When they encounter plant roots, they curl themselves around the roots, anchor themselves with their jointed legs, and begin feeding.
Feeding Japanese Beetle grubs do tremendous damage to the plants upon which they feed in two ways: directly and indirectly.
How Japanese beetle Grubs Cause Direct Damage To Plants
Japanese Beetle grubs cause direct damage to plants because their feeding destroys the roots’ ability to absorb water and nutrients from the soil. The grubs sever the connection between the root hairs and the soil by tunneling around underground and also chew the roots away completely. This causes nutrient deficiencies and water stress that cause the plants to wilt, become stunted and eventually die.
In some cases, the grubs can actually chew through the entire anchoring stem of a plant, causing it to topple over and die quickly. Until they’re ready to overwinter, Japanese Beetle grubs stay in the upper portion of the soil, where the roots of their food plants tend to be, and tunnel sideways. In heavy infestations, the grubs can sever so many individual grass plants that the turf can be lifted up like a rug laid on top of the soil.
How Japanese Beetles Grubs Cause Indirect Damage To Plants
Japanese Beetle grubs do plenty of damage to plants directly but they also hurt the plants upon which they feed indirectly. As the plants weaken thanks to the Japanese Beetle grubs chewing up their roots, they become more susceptible to other pests, like other plant-feeding insects, fungi, and bacterial infections.
Eventually, the damage become too great for the plants to withstand, and they die.
What Do Japanese Beetle Grubs Eat?
Japanese Beetle grubs feed on the roots of turf grasses—both wild and cultivated. These include:
- Kentucky Bluegrass
- Perennial Ryegrass
- Tall fescues
- Bentgrass (Watschke, Dernoeden, and Shetlar 2013)
They also feed on strawberry roots and a wide variety of other ornamental and garden plants.
Is There Anything Japanese Beetles Won’t Eat?
Japanese Beetles are so abundant across the eastern United States—and do so much damage to our wild, garden, and agricultural plants—that they seem like they eat everything.
While this insect species does do tremendous damage every year, surprisingly, there are some plants that they don’t seem to care for, probably because these plants manufacture some kind of chemicals that deter the beetles (Resh and Carde 2009).
These include (courtesy of “The Handbook of Vegetable Pests”, by John L. Capinera):
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Artichoke |
Brussels Sprouts |
Cabbage |
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Cantaloupe |
Carrot |
Cauliflower |
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Celery |
Cucumber |
Eggplant |
|
Lettuce |
Onion |
Peas |
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Parsley |
Pepper |
Pumpkin |
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Spinach |
Squash |
Sweet Potato |
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Turnip |
Watermelon |
Interestingly enough, one type of plant damages Japanese Beetles in return when its chewed up by the adult insects.
Geraniums are a type of very pretty flowering plants in the genus Pelargonium used extensively in home landscaping and gardens. Its leaves are toxic to Japanese Beetles. After beetles eat geranium leaves, they become paralyzed (Resh and Carde 2009).
What Eats Japanese Beetles?
Many animals eat Japanese Beetles, although they don’t control the population very well. Even though Japanese Beetles are entirely edible insects, they aren’t native to the United States so no natural predator evolved to prey upon them.
The predators that do eat Japanese Beetles have learned to consume them but also consume many other native insects as well, so this invasive species has spread across the central and eastern United States.
Predators of Japanese Beetles include:
- Mammals, like Virginia Opossums, Common Raccoons, Striped Skunks, moles, and shrews
- Birds, like Grackles and Starlings
- Predatory insects like ground beetles, assassin bugs, and ants
- Lizards like Green Anoles
- Predatory fish like trout and bass
For detailed information about all the different animals that eat Japanese Beetles, check out this Now I Wonder post, “The Complete Guide To The Animals That Eat Japanese Beetles“.
Japanese Beetle Behavior And Life Cycle
Like all insects, Japanese Beetles develop through four distinct life stages: egg, larva, pupa, and adult.
Egg Stage
Mated female Japanese Beetles lay approximately 40-60 eggs in their lifetime, but lay only a few eggs at a time and alternate periods of feeding and egg-laying.
Japanese Beetles lay their eggs in the top 8 cm of soil, usually in moist areas near preferred larval food plants. Females burrow down using special spurs on their forelegs, lay a few eggs, then abandon the eggs to develop on their own.
Japanese Beetle eggs must remain moist or they’ll desiccate and die.
Larval and Pupal Stages
Japanese Beetle eggs hatch into larvae called “grubs”.
Japanese Beetle grubs are soft-bodied, translucent or creamy white, and have brown head capsules, three pairs of jointed legs, and long, segmented abdomens. They feed underground on plant roots and develop through three growth stages called “instars”.
In North Carolina, Japanese Beetle grubs overwinter as second or third instars. As fall approaches, the grubs leave the upper few inches of soil and dig themselves deeper into the soil, where they remain through the winter. In the spring, they burrow back towards the surface and feed for a few more weeks. Then they return to deep soil, pupate, and eventually emerge as adults.
Adult Stage
Adult Japanese Beetles live for only one summer season in North Carolina and can be found June through August.
As soon as adults emerge, they have two primary goals: eating and mating. Scent is important to both activities.
Adult Japanese Beetles are attracted to certain food plants by the feeding activity of other beetles. When they emerge in the spring, adult Japanese Beetles immediately find food plants and settle in for serious feeding. They chew out the tissue between the leaf veins, which causes the plants to release chemicals that attract other Japanese Beetles. Large numbers of Japanese Beetles end up feeding in small, concentrated areas.
Virgin females release pheromones that attract males from long distances. Males attempt to mate with the females and often form large balls consisting of a single female Japanese Beetle surrounded by many, many males.
In my experience, Japanese Beetles pair off for mating more often in the morning when temperatures are cooler than they will be later in the day.
Not every pairing results in copulation, and some pairs are actually male-male instead of male-female. The only way to know for sure which is which is to inspect the forelegs of the bottom beetle; female Japanese Beetles have flattened, spatula-shaped spurs on their forelegs that they use to dig soil for egg-laying, while males have sharper spurs.
May i Cut In? Male-Male Japanese Beetle Competition For Females
Mating is serious business in the animal world, and Japanese Beetles are no exception.
The habit of Japanese Beetles to congregate in small areas for feeding also helps them reproduce. In the world of Japanese Beetles, proximity to members of the opposite sex matters. In general, the first male to pair with a female mates successfully, so it pays off for individual beetles to stay close to one another.
Female Japanese Beetles may mate with more than one male over the course of a season, so male to male fights for the right to mate are not very common in this species. But they do happen.
One research study completed by Kipp C. Kruse and Paul V. Switzer published in the Journal of Insect Science found that fights between males occurred in only a small percentage of Japanese Beetles studied (Kruse and Switzer 2007, https://doi.org/10.1673/031.007.3401).
When fights did occur, intruding males attempted to pry resident males off their females by sheer force. Intruding males approached the male-female pair from the front or from behind, shoved their heads between the two insects, and used their legs to try and lever the resident males off the females.
Japanese Beetles seem to fight by brute force only; the researchers observed no evidence of males biting each other during fights (Kruse and Switzer 2007, https://doi.org/10.1673/031.007.3401).
Unfortunately for the intruding males, their efforts failed often. In 74% of the fights, the resident males maintained control of the females with whom they were paired, thwarting the intruding males’ takeover attempts (Kruse and Switzer 2007, https://doi.org/10.1673/031.007.3401).
However, sometimes the strategy worked and the intruding males successfully pried resident males of their chosen females. In these cases, the displaced males attempted to regain the females but failed every time.
So even though the strategy doesn’t often work, it works often enough that male Japanese Beetles seem to feel it worth their time and energy to try.
Once mated, female Japanese Beetles fly off to lay their eggs in the soil, then return to their food plants to eat, and repeat the cycle up to 15 times in a season (Resh and Carde 2009). Adults are killed off by the first frost but the grubs survive the winter by resting deep in the soil until warm weather returns.
Japanese Beetle Classification
|
Phylum |
Arthropoda |
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Class |
Insecta |
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Order |
Coleoptera |
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Family |
Scarabaeidae (Scarab Beetles) |
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Genus |
Popillia |
|
Species |
P. japonica |
Binomial Name |
Popillia japonica |
