- Scientific Name: Popillia japonica Newman [Phylum Arthropoda: Class Insecta: Order Coleoptera: Family Scarabaeidae]
- Common Names: Japanese beetle
- Climatic Zone: temperate
- Geographic Distribution: This imported pest is generally found east of a line roughly running from Michigan, southern Wisconsin and Illinois south to Alabama. Established, localized populations are also known in Nebraska, Iowa, Missouri and northern Arkansas. Occasional introductions are made into western states such as California, Nevada and Oregon when the adult beetles or larvae are shipped in commerce. The original population was detected in New Jersey in 1916 having been introduced from Japan.
- Damaging Stage: adults (on ornamental plants) and larvae (in turf)
- Hosts: The adult beetles are general herbivores and are known to feed on over 400 species of broad-leaved plants, though only about 50 species are preferred. The grubs will also feed on a wide variety of plant roots including ornamental trees and shrubs, garden and truck crops, and turfgrasses. They seem to especially relish Kentucky bluegrass, perennial ryegrass, tall fescues and bentgrass.
- Damage Symptoms: The adults are skeletonizers, that is, they eat the leaf tissue between the leaf veins but leave the veins behind. Attacked leaves look like lace which soon withers and dies. The adults will often attack flower buds and fruit. The grubs can kill small seedling plants but most commonly damage turf. The turf first appears off color as if under water stress. Irrigating often masks infestations, but when withdrawn, severe damage soon appears. The turf feels spongy under foot and can be easily pulled back like old carpet to reveal the grubs. Large populations of grubs kill the turf in irregular patches.
- Description of Stages: The life stages of the Japanese beetle are typical of white grubs.
Eggs: The white oval eggs are usually about 1/16 inch (1.5mm) long and 3/64 inch (1.0mm) wide. They are placed singly or in small clusters in the soil where they absorb moisture and become more round.
Larvae: The larvae are typical white grubs which can be separated from other soil dwelling white grubs by the presence of a V shaped series of bristles on the raster. First instar larvae are about 1/16 inch (1.5mm) long while the mature third instars are about 1-1/4 inch (32mm) long.
Pupae: The pupae are cream colored first and become light reddish brown with age. The average pupa is about 1/2 inch (14mm) long and 1/4 inch (7mm) wide.
Adults: The adults are a brilliant metallic green color, generally oval in outline, 3/8 inch (8-11mm) long and 1/4 inch (5 7mm) wide. The wing covers are a coppery-brown color and the abdomen has a row of five tufts of white hairs on each side. These white tufts are diagnostic. The males have a sharp tip on the foreleg tibia while the female has a long rounded tip.
- Life Cycle and Habits: Larvae that have matured by June pupate and the adult beetles emerge during the last week of June through July. On warm sunny days the new beetles crawl onto low growing plants and warm for a while before taking flight. The first beetles out of the ground seek out suitable food plants and begin to feed as soon as possible. These early arrivals begin to release an aggregation pheromone (odor) which is attractive to adults which emerge later. These odors attract additional adults to gather in masses on the plants first selected. In cool weather, the adults may feign death by dropping from the plants but normally they will take flight.
Newly emerged females release an additional sex pheromone that attracts males. The first mating usually takes place on the turf with several male suitors awaiting the emergence of a new female. Mating also is common on the food plants and several matings by both males and females is common. After feeding for a day or two, the females leave feeding sites in the afternoon and burrow into the soil to lay eggs at a depth of 2 to 4 inches. Females may lay 1 to 5 eggs scattered in an area before leaving the soil the following morning or a day or two later. These females return to feed and mate. This cycle of feeding, mating and egg laying continues until the female has laid 40 60 eggs. Most of the eggs, 75% of a population, are generally laid by mid August though adults may be found until the first frost of fall.
If the soil is sufficiently moist, the eggs will swell in a day or two and egg development takes only 8 to 9 days at 80 to 90 °F or as long as 30 days at 65 °F. The first instar larvae dig to the soil surface where they feed on roots and organic material. If sufficient food and moisture are available, the first instars can complete development in 17 days at 78 °F or as long as 30 days at 68 °F. The second instars take 18 days to mature at 78 °F and 56 days at 68 °F.
During development, grubs may tunnel laterally in search of organic matter and fresh roots. This creates a very spongy feel to the soil and turf. Generally most of the grubs are in the third instar by early mid-October and are ready to dig into the soil to spend the winter. The grubs move down 4 to 8 inches into the soil as cold temperatures arrive. At this depth the soil rarely gets below 25 °F and the grubs survive with no difficulty. If the soil begins to cool further, the grubs may dig deeper. Japanese beetle grubs have been recovered at a depth of 30 inches in Canada during the winter months.
The grubs return to the surface in the spring as the soil temperature warms. Generally the grubs can be expected to be active at the surface when the surface soil temperatures are about 60 °F, usually in mid April. The grubs continue their development in the spring and the few second instars seem to mature in time to pupate along with the third instars. The mature grubs form a prepupa in late May to early June. The prepupa voids its gut contents and has a translucent appearance. The pupa is formed in the split skin of the prepupa in an earthen cell 1 to 3 inches in the soil.
- Control Approaches:
Cultural Control - Quarantine - Japanese beetle quarantines are currently operated by the USDA-APHIS and states involved with shipping materials out of infested areas to uninfested places. Though this has not stopped the slow progression of Japanese beetles westward, it seems to have slowed the process. Nurserymen and sod producers shipping plant material with soil out of Japanese beetle infested areas must obtain an inspection and certification. Often airports and rail yards are under quarantine and transporters must treat their containers before shipping.
Cultural Control - Habitat Modification - Japanese beetle eggs and young grubs are very susceptible to desiccation in dry soils. Therefore, omitting irrigation during the time eggs and first instar larvae are developing is detrimental to the insect. However, if natural rainfall occurs this tactic will not work. Do not plant trees or shrubs highly attractive to adult Japanese beetles near the turf. This is especially true along golf course fairways. Trees and shrubs most attractive to adults include: Japanese and Norway maple, birch, pin oak, horsechestnut, rose of Sharon, sycamore, ornamental apple, plum and cherry, rose, mountain ash, willows, lindens, elms, and Virginia creeper. Trees and shrubs rarely attacked include: red and silver maple, holly, boxwood, euonymus, flowering dogwood, cedar, juniper, arborvitae, red oak, tuliptree, magnolias, red mulberry, forsythia, ashes, privet, lilac, spruces, hydrangeas, and taxus (yew)
Cultural Control/Mechanical Control - Trapping - Several traps have been developed to capture the adults. These traps generally use a mixture of the aggregation and sex pheromones. Recent data indicate these traps do not significantly reduce grub populations and in some cases may actually contribute to increased foliar plant damage. There has been no correlation between trap captures and reductions in white grub populations in surrounding turfgrass areas.
Biological Controls - Insect Parasites - Several parasitic wasps, especially Tiphia popilliavora and T. vernalis, and the winsome fly, Hyperecteina aldrichi, have been imported and are now known to be established in several eastern states. Unfortunately, these parasites do not seem to be reliable in reducing Japanese beetle populations below damaging levels. However, the Tiphia appear to be more efficient in southern states.
Biological Control - Bacterial Milky Disease - The bacterial milky disease, caused by Phaenobacillus popilliae Dutky and P. lentimorbus Dutky, has shown some effectiveness at controlling the grubs in certain areas of the eastern United States. The spore count in the soil requires 2 to 3 years for some effectiveness. During this time grubs should not be killed with insecticides in order for the bacterium to complete its cycle. There are recent data that suggests these bacterial diseases may not be performing well in certain areas. This may be due to reduced virulence or adverse soil conditions. More commonly, different white grub species have displaced the Japanese beetle grubs. In Ohio and Kentucky, test trials with milky diseases have not produced satisfactory results. Additional experiments are needed to determine the causes of this lack of efficacy.
Biological Control - Insect Parasitic Nematodes - The insect parasitic nematode, Steinernema glaseri Steiner, was used before 1940 and had considerable promise but this agent was not developed further because of problems of rearing and expense. This nematode may be economically available in the future. Commercially available products containing strains of S. carpocapsae' have been marginally effective. Preparations containing Heterorhabditis spp. seem to be the most effective of the currently available nematodes. Nematodes should be applied when white grubs are in the second instar. Irrigation before and after nematode application with 1/4 inch of water minimum increases efficacy.
Chemical Control - Insecticides -
Targeted Treatments. Insecticides are most effective when small stage grubs are the target. First instar Japanese beetle grubs are present from late July through mid-August. Applying an insecticides at this time, followed by sufficient irrigation to move the insecticide to the grubs usually yields satisfactory results.
First instar grubs molt into second instars which feed from mid-August through September. These middle stage larvae are also very susceptible to control, but if not controlled, turf damage may begin to appear in mid-September. From late September through October, most grubs reach the third instar stage and are 40 to 60 times the body weight of the newly hatched, first instars. By this time, significant damage may be evident and skunks and racoons often dig up infested turf to feed on the grubs.
Curative Treatments. Most insecticide applications made in late September and October yield poor control of third instar grubs. At this time, insecticides known to have rapid action and are least affected by thatch binding are effective.
In late April and May, Japanese beetle grubs return to the upper soil level to briefly feed. Though grub damage may be evident at this time, skunk and racoon digging is usually the major problem.
Preventive Treatments. The recent labeling of long residual (>120 days) insecticides has made it possible to obtain grub control with a single application in May, June, July or August. Depending upon the time of application, some of these new insecticides simultaneously provide control of a broad range of insect pests other than grubs. Unlike carbamate or organophosphate insecticides, these new materials have low inpact on beneficial organisms that live in the turf. Both liquid and granular formulations are available. Some require posttreatment irrigation, others do not. Read and follow label instructions for optimum results.
Preventive treatments are most warranted where the risk of grub infestation is greatest. Recent research has shown that turf areas that have experienced a damaging grub infestation are more likely to experience a reoccurring damaging infestation. Likewise, certain golf course areas and lawns in neighborhoods often have reoccurring infestations. These are likely candidates for preventive treatments.
Grub infestations should be evaluated as early as possible by monitoring, accurate identification and mapping of infested areas. The standard golf course cup cutter is a convenient tool to survey for infestations in golf courses, sports turf and home lawns. If care is exercised, sampling can be done with minimal damage to the turf. Once removed, samples can be examined carefully on the spot. Each soil and turf core is placed back in the hole made by the sampler. The sample does not have to be completely torn apart to determine the number of grubs present. If the soil is dry, it is advisable to add water to the sample hole before replacing the sample to improve the turf survival.
The standard cup cutter is 4-1/4 inch in diameter. Therefore, to convert the number of grubs found per sample to the number of grubs per square foot, multiply the average per sample by a factor of 10.15.
Golf Course - Starting at the tee end of a fairway, take the first sample five feet in from the rough, the next sample in the center of the fairway, and the next at the edge of the rough on the other side of the fairway. Zig-Zag sample in this manner to the green. For roughs, number each sample and note the direction of the sample pattern on a rough drawing for later mapping. Record the number, size and species of grubs found in each sample. Do not leave blanks on the recording form; if no grubs, enter a zero. If identification is in doubt, keep a generous sample of the grubs, place them in 20% alcohol and send them to a specialist for identification.
Lawns, Grounds and Athletic Fields - Sufficient samples should be taken to determine the location and severity of grub infestation (i.e., mapping). Samples taken on a 10 foot grid pattern (larger distances for very large lawns) is often recommended. Concentrate samples in areas that are predominately sunny sites. While using a cup changer works well, using a knife or spade to cut V-shaped cuts in the turf which are pulled back, examined for grubs and replaced, also works well. Though less precise, this method will provide a general map of infested areas.
Many books and extension publications on grub management often mention “population thresholds.” Thresholds are the numbers of pest insects present in a given area (usually per square foot) that warrant control. The principle behind using thresholds is to reinforce the IPM principle that application of a pesticide is not always warranted simply if pests are present. Pests must be present at populations high enough to eventually cause damage.
The generally accepted level for Japanese beetle is 6 to 10 grubs/ft2, before control is warranted. However, well maintained turfgrass with regular irrigation and fertilization can “tolerate” much higher grub populations. On the other hand, moles, skunks and racoons often find less than six grubs per ft2 sufficient to dig up the turf in search of them.
Thresholds must be adjusted for each turf situation. For golf courses, damage in roughs is more tolerable than damage in fairways, and damage in fairways is more tolerable than damage on tees and greens. Likewise, some course or home owners demand high turf standards while others may tolerate some periodic, localized damage.