Japanese Beetle

Dominique Ebbenga, S.J. Wold-Burkness, E.C. Burkness, & W.D. Hutchison
Department of Entomology, University of Minnesota

Introduction

Japanese Beetle on grape
Figure 1. Japanese beetles on grape leaves (S.J. Wold-Burkness, UMN)

Japanese beetle (Popillia japonica) is an invasive species first detected in America in 1916 in New Jersey after an accidental introduction. Japanese beetle is native to Japan, where it is regarded as a minor agricultural pest. Since first arriving in America, Japanese beetle has spread throughout the eastern U.S., excluding Florida, and has continued to move westward.

Japanese beetle was first found in Minnesota, in 1968. Since their arrival, populations have fluctuated from year to year. Current research demonstrates that in high density years traps can catch >5,000 beetles per day. The Minnesota Department of Agriculture keeps an updated map on their website illustrating the spread within the state. 


Identification

Adult Japanese beetle can be identified by a metallic green head and thorax, copper brown wing covers, five white hair tufts on the side of their abdomen, and two tufts on the rear of their abdomen (Fig. 2). Their size ranges between 1/3 to 1/2 inch. The white tufts of hair distinguish them from the sand chafer or false Japanese beetle as the sand chafer does not have the hair tufts but otherwise look very similar in size and shape (Fig. 3).

Japanese Beetle
Figure 2. Japanese beetle adult (Joseph Berger, Bugwood.org)
False Japanese Beetle
Figure 3. False Japanese beetle adult (Whitney Cranshaw, Colorado State University, Bugwood.org)

Larvae, also known as white grubs, are found in the soil where they feed on grass roots. They are c-shaped, with a white to cream colored body, tan head capsule, and covered in small brown hairs (Fig. 4). Depending on the larval stage, they can be anywhere from 1/8 to about an inch long. They can be very difficult to distinguish from other grub species found in the soil. Proper identification of Japanese beetle larvae requires looking at raster patterns and slit shapes on the rear of the insect (Figure 5). 

Japanese Beetle larva
Figure 4. Japanese beetle larva (David Cappaert, Bugwood.org)
Japanese Beetle larva
Figure 5. Close up view of Japanese beetle larva showing raster pattern (Michael Reding, USDA Agricultural Research Service, Bugwood.org)

Life Cycle

Japanese beetle overwinters below the soil surface as larvae between 1 and 6 inches deep (Figure 6). Once spring begins, the larvae will begin to move up to the soil surface to resume feeding on grass roots until they reach pupation. Once they have pupated, you can expect to see adults emerging from the soil at the end of June to early July and begin feeding on host plants, including ornamental and agricultural crops. While adults feed, they will mate and move from host plants to areas of sod or other grasses to lay eggs beneath the soil. Eventually, the eggs will hatch, and larvae will undergo three larval stages (instars) and remain in the soil feeding as they burrow deeper into the soil to overwinter.

Diagram of Japanese Beetle life cycle
Figure 6. Life cycle of Japanese beetle (Marlene Cameron, Michigan State University)

Damage

Damage can be caused by both adults and larvae. Adults feed on the above ground plant parts, including flowers, leaves and fruit of >300 plant species. However, the larval stage feeds exclusively on grass roots.

Preferred fruit crops include grapes, raspberries, and apples. In addition, many ornamental plants are impacted as well, including rose, linden, and crab apple. When adults feed on crop foliage, they create a distinctive pattern of defoliation on the leaf known as “skeletonization” (Fig. 7). They do this by eating the tissue in between leaf veins. In some cases, leaves can become severely defoliated, turn brown, and drop off the plant, reducing photosynthesis. As beetles feed chemical signals are released which attract other beetles to the crop (Figs. 8-10). Feeding will usually begin at the top of the canopy on new foliage and may eventually move to older foliage when populations are high. 

Adult Japanese beetle damage can be alarming when beetle density is high and can lead to severe defoliation. However, it has still not been determined if this damage will impact crop yield. For perennial crops such as grapes and raspberries, older, well established plants seem to be able to recover from feeding damage, but long-term effects are unknown. Younger, less established plantings, however, may have stunted growth if feeding damage is severe. As populations continue to increase and spread across Minnesota, it is important to determine the potential economic impact this pest could have in the future. 

Japanese Beetle damage
Figure 7. Skeletonizing of leaves caused by Japanese beetle feeding (S.J. Wold-Burkness, UMN)
Japanese Beetle on sweet corn
Figure 8. Japanese beetles feeding on sweet corn silk (E.C. Burkness, UMN)
Japanese beetles on raspberry
Figure 9. Japanese beetles on raspberries (S.J. Wold-Burkness, UMN)
Japanese beetles on raspberry
Figure 10. Japanese beetles feeding on raspberry leaves (E.C. Burkness, UMN)

Adults prefer to lay eggs in grassy areas and due to the limited mobility of the larvae, they are typically found feeding on grass roots. Overwintering larvae feed on grass roots from April to the end of May, and once newly laid eggs have hatched, larvae feed from August to November. Larvae damage grass by pruning off the roots which reduces water uptake. This feeding damage can result in brown patches of sod that easily lift up from the ground when larval densities are high.


Management

Adults

Due to the lack of research on the impact of Japanese beetle feeding on crop yield and quality, economic thresholds have not been established for this pest on many crops.

If populations are high and growers are concerned about excessive defoliation in a crop, the use of insecticides, such as carbamates and pyrethroids, or organic options such as Entrust or Pyganic can be effective management tools. Always be sure to read labels carefully and follow recommended rates for application.

Alternative managment options have not been studied extensively, however, the use of physical barriers, such as exclusion netting or high tunnels, may be used to prevent the beetle from infesting the crop.

In its native range, biological control agents have been a major help in reducing the pest status of this insect. However, when Japanese beetle was introduced to the U.S., these biological control agents were not present to help manage population levels. Currently, one native biological control agent that has been found in Minnesota, is the winsome fly (Isocheta aldrichi). This fly lays its eggs on the heads of adult Japanese beetle (Figs. 11 and 12). Once eggs hatch, larvae burrow into the host and feed, eventually killing the beetle. Unfortunately, life cycles of the two insects are not in synchrony (i.e., as Japanese beetle is just beginning to emerge, the winsome fly is within the last three weeks of its activity for the year). Continued monitoring and studies on this biological control agent will help to better understand the potential of this being a feasible control option in the future.

Parasitized Japanese beetle
Figure 11.
Japanese beetle parasitized by Isocheta aldrichi (Whitney Cranshaw, Colorado State University, Bugwood.org)
Parasitized Japanese beetle
Figure 12. Egg and pupa of Isocheta aldrichi (Whitney Cranshaw, Colorado State University, Bugwood.org)

Larvae

Typically, larval control is pursued with the intent of impacting next seasons populations. So, when controlling larvae, it is important to keep in mind this will not have an impact on the current season's adult population. Also, it is important to keep in mind, beetles can fly from surrounding locations, therefore controlling the larval stage may not be effective if neighboring areas are not treated. Larval management focuses on turf areas where eggs are laid, and larvae develop. Applications of conventional insecticides or biologicals such as Bacillus thuringiensis can be made to turf in late August to early September (see Fig. 2) to control larvae in the early growth stages and before they travel too deep in the soil.


Related References

Japanese Beetle in Yards and Gardens, Jeff Hahn and Julie Weisenhorn 2018: https://extension.umn.edu/yard-and-garden-insects/japanese-beetles

Japanese Beetles (E0010TURF), Davis 2018: https://www.canr.msu.edu/resources/japanese_beetles_e0010turf

Biology and Management of Japanese Beetle (Coleoptera: Scarabaeidae) in Corn and Soybean, H.N. Shanovich et al. 2019: https://academic.oup.com/jipm/article/10/1/9/5454734

Biology and Management of the Japanese Beetle, Potter and Held 2002: https://www.annualreviews.org/doi/full/10.1146/annurev.ento.47.091201.145153 

Biology of the Japanese Beetle, Fleming 1972: https://naldc.nal.usda.gov/download/CAT87201410/PDF