Oriental Beetle

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Oriental beetle adults showing common color forms.
Oriental beetles have two parallel rows of small bristles in the raster pattern, often with another adjacent set of larger bristles.
  • Scientific Name: Anomala (Exomala) orientalis Waterhouse. [Phylum Arthropoda: Class Insecta: Order Coleoptera: Family Scarabaeidae]


  • Common Names: Oriental beetle


  • Climatic Zone: temperate


  • Geographic Distribution: This native of Japan was first detected in the United States in Connecticut in 1920. This pest moved little from that time to the mid 1970s. It has since moved, mainly in soil of nursery stock, to periodically damage turf in northeastern Ohio, New York, Pennsylvania, New Jersey, most of the New England States and down to the Carolinas.


  • Damaging Stage: The larvae damage turf, and the adults often feed on flowers.


  • Hosts: The larvae readily attack the roots of cool-season turfgrasses such as Kentucky bluegrass, perennial ryegrass and fescues where they often occur in mixed populations with the Japanese beetle. Occasionally, they will feed on roots of weeds and are known to damage full grown nursery stock and outdoor potted plants.


  • Damage Symptoms: Grubs feed destroy turf roots as the feed on the organic matter close to the surface (e.g., thatch) causing typical grub damage consisting of wilting turf which may die in irregular patches. This pest prefers to feed on turf in sunny areas. Oriental beetle grubs in container plants can almost completely destroy the fine roots causing the plant to wilt and not hold onto the pots.


  • Description of Stages:


Eggs: The white eggs are first oval in shape, being 3/64 by 1/16 inch (1.2 by 1.5 mm), and swell to 1/16 by 5/64 inch (1.5 by 1.9 mm) after a few days in moist soil.

Larvae: Mature third instar Oriental beetle grubs are approximately the same size and externally resemble Japanese beetle grubs. Mature grubs are about 1 inch (25 mm) long. The anus is transverse and the raster has two parallel rows of about 14 short stout spines. These could be confused with young May-June beetle larvae. However, the difference is that May-June beetle larvae have a broad V shaped anal opening and that of the oriental beetle is a transverse curve.

Pupae: The pupa is about 3/8 inch long and 1/4 inch wide (10 by 5 mm). They are first cream colored and turn to light brown. The tip of the abdomen has a thick fringe of hair like setae.

Adults: The adults are 3/8 to 7/16 inch long (9 to 10 mm) and vary considerably in intensity of the markings on the thorax and wing covers. Individuals may be entirely brownish black to entirely straw colored except for a brown head and mark on the pronotum. Usually the head is solid dark brown, the pronotum is dark in the center outlined in straw color, and the wing covers have longitudinal grooves and are mottled with patterns of dark brown on straw. The head and prothorax are usually iridescent bronze in bright light.


  • Life Cycle and Habits:

The adults begin to emerge in late June and some may be found as late as September. Adults are most active in July. They may fly short distances in the morning but are most active in the evenings where they are commonly found chewing on petals of flowers. Some of the adults are attracted to lights but never in large numbers. A few days after mating, the females burrow into the soil to lay eggs. Females lay an average of 26 eggs in small groups between 3 and 9 inches in the soil. The eggs must be in moist soil so that water can be absorbed and development continued. At normal soil temperatures in July and August, the eggs take 18 to 24 days to hatch. The young grubs move to the soil surface to feed on roots and organic material. The second instar larvae are found in 3 to 4 weeks and these usually molt into third instars in another 3 to 4 weeks. The majority of the larvae overwinter as third instars but some overwinter in the second instar. Larvae burrow down late October and November and return to feed the following April and May. The pupae are present from mid- to late June and usually take about two weeks to mature.


  • Control Approaches:

Cultural Control - Habitat Modification - Since the eggs require moisture for development, restricting irrigation in late June into early August may significantly reduce survival.

Natural Control - Milky Diseases - Milky diseases caused by strains of Phaenabacillus popilliae are known but commercial preparations do not contain Oriental beetle-specific strains.

Biological Control - Entomophagous Nematodes - The insect parasitic nematode, Steinernema glaseri, 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. As with most soil-inhabiting insects, insecticides are most effective when small stage grubs are the target. For Oriental beetles, the small first instar grubs are present July through early August, unless a severe drought has occurred. In this case, the adults may delay egg laying and sampling should be performed about four weeks after normal soil moisture returns. Applying an insecticide 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 that 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 by mid-September. From late September to October, Oriental beetle 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 caused by skunks and racoons who dig up infested turf to feed on the grubs.

Curative Treatments. 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, Oriental beetle grubs return to the upper soil level to briefly feed. Though grub damage may be evident at this time, skunk and racoon damage is usually the major problem. If necessary, insecticides with rapid action may be used.

Preventive Treatments. The recent labeling of long residual (>120 days) chloronicotinyl and diacylhydrazine 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 impact 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.


Monitoring

The adults can be monitored using a recently developed pheromone. This pheromone is not readily available on a commercial basis, but may be so in the near future. If drought conditions occur in late June and July, Oriental beetle adults may delay laying eggs. Traps may assist in determining if adult flights are normal or delayed. When the trap capture has decreased for ten days, mark the date of peak activity. The grubs will be most susceptible to controls about six weeks after this peak.

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 which are usually concentrated in sunny, actively growing turf. 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.


Thresholds

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 concept 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 Oriental beetle is 8 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 square foot 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.