Japanese Beetles

Often homeowners notice the skeletonization of the leaves of plants and trees or brown patches of grass. Flower blossoms may look stunted or you might see a jagged pattern around the edges of the petals.

It is easy to see the adult Japanese beetles as they land and feed on the leaves of plants and trees.

Unlike May or June beetles, Japanese beetles are most active during the day. However, the adults are known to be less active in the early morning or late evening.

Adult Japanese beetles about 1/3” to ½” long and have a shiny, metallic-green body and bronze-colored elytra (wing covers). The copper or bronze colored elytra appear metallic in the sunlight. There are six small tufts of white hairs along its side.

Japanese beetle larvae, often referred to as grubs or white grubs, have a brown head and grayish-black rear end. They are C-shaped and reach about 1” long at maturity. Hairs on the last body segment (raster) have “V” shape pattern just below the anal opening.

Pupae are about ½” long with a cream color and become light reddish-brown with age.

Japanese beetle eggs are creamy white, oval and about 1/16” long when first laid. As the embryos develop, eggs normally enlarge to double their initial size and become almost round.

There is no evidence to suggest that Japanese beetles bite.

They may try to pinch you with their mandibles, but the Japanese beetles’ mandibles of are too weak to hurt you or to damage human skin.

Japanese beetles have rough spines on their legs that might feel prickly against your skin.

It is unlikely that Japanese beetles will do any damage to structures.

However, Japanese beetles can cause significant damage to outdoor plants.

A single beetle doesn’t eat much, but large congregations of feeding Japanese beetles are what really destroy plants.

While adult beetles cause the most visible damage to plants’ leaves, the beetle larva can also be particularly harmful to plants’ roots.

Large numbers of Japanese beetle larvae can attract predators like skunks and moles, which will dig up turf to unearth grubs and cause more damage in the process.

Japanese beetles produce sex and aggregation pheromones. Virgin females emit the sex pheromone to lure males for mating purposes. The aggregation pheromone is used to attract other Japanese beetles to new feeding sources.

Wounded leaves and flower petals also release a chemical (kairomones) that adult Japanese beetles can detect. This explains why Japanese beetles are normally seen feeding in groups.

Japanese beetles can fly as far as five miles for ideal conditions.

Turf that is regularly irrigated can also attract egg-laying Japanese beetle females

Japanese beetles feed on foliage, flowers, or fruits of more than 300 plant species in 79 plant families.

Favorite plants of the Japanese beetle include roses, hibiscus, grapes, raspberries, linden, sassafras, Japanese maple and Norway maple.

Evergreens, red maple, flowering dogwoods, and lilacs, as well as many truck crops, field crops, ornamental flowers, and grains, are seldom damaged by Japanese beetles. For example, Japanese beetles normally avoid pear trees.

Japanese beetles usually start at the top of a plant and work their way downward. Adults feed on the upper side of the leaves leaving only the veins and midribs undamaged. This typically gives the leaves a skeletonized appearance.

Japanese beetles feed on the low plants in the beginning before they move to feeding on foliage of trees.

Larvae feed on surrounding grass roots and decayed organic matter in the soil.

The life cycle of the Japanese Beetles consists of four stages of development called complete metamorphosis. These stages are egg, larva, pupa and adult.

Adult Japanese beetles have a short lifespan: 30-45 days on average.

Mating is common on the food plants during feeding and several matings by both males and females are common.

Female Japanese beetles will leave the plant on which they are feeding to find ideal soil conditions in which to lay their eggs.

At each egg laying, female Japanese beetles deposit one to five eggs 2 to 4 inches deep in the soil.

Females feed, mate and lay eggs — repeating the process every 24 to 48 hours. This process will repeat itself until the female lays 40 eggs throughout her life cycle.

The eggs develop into larva, often called “grubs”, and can spend the fall and winter months in the ground developing toward the pupation stage.

The larvae go through 5 instars or molts before pupating into the adult form.

The larvae survive on proper soil moisture and often feed on the nearby grass or crop roots.

Once the larvae fully develop, they enter the pupation stage and become adults.

The adult stage is typically reached in the early summer months, and the adult Japanese beetles leave the ground and immediately look for plants on which to feed.

These newly formed adult Japanese beetles begin to release pheromones to attract other adult Japanese beetles.

Once other adult Japanese beetles arrive, they begin the feeding/mating cycle over again.

Both grubs and adults need to be managed.

The timing of the insecticide applications is crucial to managing Japanese beetles. This requires the understanding of the pest life cycle and continuous observation of the weather conditions.

To manage adult beetles, treatments to infested foliage should be done June through August.

Adam’s does not treat edible plants infested with Japanese beetles.

Adult Japanese beetles like the sun – they prefer to feed and mate on warm, sunny days.

The coppery-green beetles were accidentally introduced to New Jersey in 1916, allegedly hidden in a shipment of iris bulbs from Japan.

Japanese beetles are still invading the United States by hitching rides on freight, vehicles, and even air cargo. Eggs and grubs travel in the soil of nursery stock.

Japanese beetles are not a major pest problem in its native Japan because of natural predators.

Japanese beetles are also known to be attracted to roses, mostly yellow ones.

When approached, Japanese beetles lift up their hind legs in an effort to scare off predators.

All species of beetles chew their food thoroughly before swallowing. A common trait all adult beetles and most beetle larvae share are mandibulate mouthparts, made just for chewing. In fact, the common name beetle is thought to be derived from the Old English word “

bitela,” meaning little bitter.

True beetles – those that resemble our modern-day beetles – first appeared about 230 million years ago, when dinosaurs still roamed the earth.