Japanese beetle grubs represent one species of scarab beetles that present a challenge to turf managers.

Japanese beetle adult

Japanese beetle adult

The Japanese beetle is one species of the white grub complex whose larvae feed on the roots of turfgrasses found in home lawns, golf courses, and athletic fields in eastern North America.

Damage caused by the larvae may begin in mid-to late August in the northeastern United States and can persist through the fall if not properly treated. Damage appears similar to drought and can often be exacerbated by drying conditions.  Damaged areas may continue to spread as the larvae continue to grow and feed through the fall.  In severe infestations, large areas of turf can be easily pulled up, as the connective roots and tissue are destroyed.  This can lead to uneven footing and injuries in sports turf, as the turf can easily slide and give way.

Aside from the larval damage, Japanese beetle adults feed on the leaves of over 250 different ornamental plants.  This damage can also be extensive, and can cause permanent damage to some small trees, as they cannot survive defoliation.

Identification of Stages

Adults

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Japanese beetle adult

The Japanese beetle adult is a striking looking insect--the head, thorax, and abdomen are bright metallic green and the legs are dark green.  Brown wing covers extend to near the tip of the abdomen, where two white tufts of hair can be found. Five similar tufts can also be found along the side of each wing cover.

Eggs

The egg is creamy white, elliptical, and roughly 1/16 inch in diameter. These eggs can be found in moist, well drained soil.

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Japanese beetle V-shaped raster pattern

All white grubs have a series of hairs and blank spaces on their back side called a raster pattern.  This pattern allows identification of the species.  Japanese beetles have a distinct V shaped pattern for their raster pattern.  Other white grub species have different patterns.

Larva

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Japanese Beetle larvae

The soft-bodied grub is "C" shaped, whitish with a brown head capsule, and is approximately 1 inch long at maturity.  The grub has 2 pairs of legs and pronounced mandibles.  A series of reddish dots run down the sides of these grubs.  These dots are actually openings in the body, called spiracles, that allow the insect to breathe. Japanese beetle larvae have three instars before they pupate.

Pupae

Japanese beetle pupae are oblong, segmented orange to brown bodies with no distinguishing features, such as legs, or eyes.  As they progress to adulthood, these pupae begin to look more like the adult.  Eventually, as they take the shape of the adult, they have become somewhat opaque, or clear.  Then as the blood enters the outer exoskeleton, the color begins to show, (melanization) and the outer body becomes hard (sclerotization).

Life History

Japanese beetles produce one generation per year.  The adults emerge from the soil in June through early July, mate, and lay eggs.  The eggs hatch in July, and the young larvae, known as white grubs, begin to feed on the turfgrass roots.  When temperatures decrease in the fall, the grubs dig down as far as 8 inches and spends the winter there.  As temperatures rise in the spring, the grubs resume feeding in the rootzone.  After a pupation period in May, the adults emerge and start the process over for a new generation

Monitoring 

Monitoring Japanese beetle populations is key to a good control strategy.  Knowing when the insect is present and knowing the population density will help you in your control decisions.  Monitoring of adult Japanese beetle populations can be accomplished using a pheromone trap.  These traps consist of a funnel with a small jar or bag attached to the bottom.  Separate lures are then attached, one lure to attract males and females (floral lure), and one to attract males (sex pheromone lure).  The beetles are attracted to these lures and fall into the jar or bag.  These beetles can then be destroyed after counting.  Careful placement of these traps needs to be considered, because huge numbers of beetles can be attracted to these traps, leading to damage of surrounding turf and/or ornamental plantings.

Monitoring white grubs can be conducted with a hand trowel or shovel. Dig a 1 square-foot by 2 inch deep piece of turf.  After removing the sample, you will need to tear it apart.  As you tear it apart, the grubs will begin to fall out.  You can then identify them by looking at the raster pattern.  You can also use a sod knife to take a smaller soil sample to accomplish this.  Golf course hole cutters are also excellent soil dwelling insect monitoring devices.  Simply remove the hole cutter plug and break into quarters over a tray.  Grubs will be near the thatch soil-interface in the fall.

Commonly accepted damage thresholds for Japanese beetle grubs is roughly 10-12 grubs per square foot.  This can vary due to turf species, plant health, and environmental conditions, such as drought or heat.

Control strategies 

Control of Japanese beetles can be done as a curative, or as preventive control.  Preventive control is usually the most optimum.  Curative controls are used once damage occurs.  Preventative control is aimed at young larvae before they have a chance to cause damage.

Cultural control

Japanese beetles prefer moist soil for egg laying.  One cultural practice that can be used is to allow the soil to dry out, making it un-attractive to egg laying females.  Dry soil can also cause the eggs to desiccate and not hatch; if the females lay eggs.  This comes at a cost though, as the turf can also become weak from the drought stress.  Removing and destroying the adult beetles can also help.  Keeping ornamental plantings and beds to a minimum can help keep the adults away as well.  According to studies conducted at Penn State, the use of a hollow- or solid-tine aerifier can provide minimal relief (~10-15% control with ½" diameter tines × 1.5" forward spacing in single events), though may provide indirect benefits to the turf (rooting, air/gas exchange) that increase the tolerance to white grub feeding.

Biological control

Entomopathogenic nematodes, which are microscopic round worms, are effective against many white grub species including Japanese beetle. Species effective at controlling Japanese beetle are cruise nematodes, such as Heterorabditis bacteriophora and Steinernema carpocapsae. Nematodes enter the grub through body openings (mouth, anus, spiracles).  Once inside, they release bacteria that kills the grub, liquifies the interior, and then use the substrate to reproduce. Eventually, the cadaver shatters, and spills forth their offspring that can then attack other grubs. Proper application techniques must be observed for maximum effectiveness, as improper application can result in greatly reduced efficacy. Ensure that nematodes are applied in low UV light conditions or watered in immediately following application. Also, removal of spray nozzles is also recommended, as the nematodes can clog the nozzles. 

Several species of wasps, and one species of fly have proven to be successful biocontrol agents against Japanese beetle grubs. Tiphia vernalis attacks overwintering grubs, whereas Tiphia popilliavora attacks younger grubs in late summer. A tachinid fly, Istocheta aldrichi, has been shown to parasitize adult Japanese beetles. Ant colonies and several species of ground beetles feed on eggs and young larvae. Avoiding broad-spectrum insecticide sprays in spring to maximize the impact that these predators and parasitoids have on white grubs.

Chemical control

Chemical control is best achieved when used preventively.  Several commercial insecticides can be effective against Japanese beetle grubs. All white grub insecticides require irrigation following the application to move the active ingredient to the rootzone where grubs are feeding.   

IRAC Code Class Active ingredient Systemic
Preventive 4A Neonicotinoid imidacloprid Yes
clothianidin Yes
dinotefuran Yes
thiamethoxam Yes
28 Anthranilic diamides chlorantraniliprole Yes
Cyantraniliprole Yes
Curative 1A Carbamate carbaryl No
1B Organophosphate trichlorfhon No
4A Neonicotinoid clothianidin Yes

Warning

The impact of several classes of insecticides on pollinating insects such as honey bees and native bees is a cause for concern. Because they are systemic chemicals absorbed into the plant, some of these products can be present in pollen and nectar, making them toxic to pollinators that feed on them. 

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.