Japanese beetle, Popillia japonica
Order: Coleoptera
Family: Scarabidae
Description
The adult Japanese beetle has an oval body and is about 15 mm (0.6 inch) in length. It is generally metallic green with coppery brown wing covers that do not quite cover the tip of the abdomen. Along the sides are five patches of white hair tufts. The antennae are clubbed at the end and may spread to a fan-like form. As adults, Japanese beetles can be found feeding and mating on foliage and flowers of their host plants.
Japanese beetle larvae are soil dwelling white grubs that feed on the roots of grasses. They are about 2-3 mm (~1/10 inch) long when newly hatched and 30 mm (~1.2 inches) long when mature. They have a creamy white body with a dark head and the legs on the thorax are well developed. Normally the body curves into a C-shape. These features are also typical of other white grubs found in association with turfgrass in Colorado, such as masked chafers and May/June beetles which are discussed in factsheet: ‘Billbugs and White Grubs’. Japanese beetle larvae are slightly smaller than these other species when full grown, but they are best distinguished by their iridescent green and copper color and the pattern of hairs on the abdomen (‘rastral pattern’), which forms a distinctive V-shape. Pupae are 14 mm (1/2 inch) long and range in color from pale white to metallic green. The eggs of Japanese beetle are white and spherical with a diameter of 1-2 mm (<1/10 inch).
Quick Facts
- Adults can feed on over 300 plant species, including a variety of vegetable crops such as basil, corn, and soybean. The larvae are soil dwelling grubs that feed on the roots of grasses.
- All beetles belong to the insect order Coleoptera, which is the most diverse insect order with over 350,000 described species. There are 30,000 species of beetle in the United States alone, though only a small fraction are pests.
- Japanese beetle traps can capture many adults but are not effective in reducing damage to nearby plants. However, trapping can be a useful monitoring tool since Japanese beetle outbreaks are difficult to predict.
Soybean leaf injured by feeding of Japanese beetle. Image credit: Roger Schmidt, University of Wisconsin-Madison, Bugwood.org
Japanese beetles on a soybean leaf. A mating pair is present on the left side of the image. Japanese beetles are an invasive insect pest in the United States and can feed on a wide range of plants. The larvae are soil-dwelling grubs that feed on plant roots, while adults feed on leaves and flowers. In Colorado, adults cause significant defoliation and damage to basil, corn, and soybean. Image credit: Roger Schmidt, University of Wisconsin-Madison, Bugwood.org
White grubs (larvae) of the Japanese beetle. Image credit: David Shetlar, Ohio State University
Homemade trap for monitoring Japanese beetle. Image credit: Jim Baker, North Carolina State University, Bugwood.org
Bean leaves skeletonized by feeding of Japanese beetles. Image credit: Bruce Watt, University of Maine, Bugwood.org
Japanese beetle parasitized by the fly, I. aldrichi. Note the presence of eggs (arrow) on the thorax. Image credit: Whitney Cranshaw. Colorado State University.
Japanese beetle trap with adults. Image credit: Karla Salp, Washington State Department of Agriculture, Bugwood.org
Life history and habits
Japanese beetle has one generation per year. Adults begin to emerge from the soil in early June and are usually most abundant in early summer – from late June through early August. Japanese beetle can attack over 300 plant species, and adults are often found aggregating on the sunny sides of plant foliage, fruit, and flowers where they feed and mate. Feeding tends to begin near the tops of plants from mid-morning until late in the afternoon or longer, depending on temperature. Mated females seek areas where soil is suitably moist to lay a small cluster of eggs among plant roots. A total of 40-60 eggs may be laid, singly, by each female beetle about 15-20 cm (5.9-7.9 inches) beneath the soil surface. The eggs hatch about two weeks later, and the grubs (larvae) begin feeding on nearby roots plants, especially grasses. Eggs and young larvae are susceptible to desiccation and may die if soil temporarily dries out during this period.
The larvae continue to feed on grass roots and develop through three instars until soil temperatures drop to about 16°C (60°F), at which point the mature larvae overwinter in the upper 5-15 cm (2-5.9 inches). In this soil zone, larvae can tolerate temperatures as low as -13°C (9°F) but will tunnel deeper in soil during extremely cold periods. Activity resumes the following spring once soil temperatures reach 10°C (50°F). The mature larvae begin to pupate in earthen cells after feeding for 4-8 weeks, and the pupal stage can last anywhere from one week to 17 days. One generation is produced per year.
Injury
While Japanese beetles can cause injury to plants in both the adult and larval stages, injury by adults is more obvious and is usually the primary concern in vegetables. Adults feed on leaves, buds, and flowers of many commonly grown vegetables. Feeding is usually restricted to the tender tissues between the larger leaf veins, which results in skeletonized leaves. Persistent and severe feeding on young or unhealthy plants can lead to stunted growth or death. Mature, healthy plants can tolerate some feeding, but severe injury can reduce plant growth and yield.
Monitoring
Trapping can be used for management when the pest population is low or as a monitoring tool in areas where Japanese beetle is established. Traps for Japanese beetle consist of a funnel on top of a cylindrical collection vessel containing floral volatiles and a female sex pheromone. These traps capture varying ratios of male/female beetles, with a greater proportion of males captured in the afternoon, and traps that are solid green tend to reduce pollinator by catch. It is important to note that, when Japanese beetle densities are high, the use of traps can lead to a “spill over” effect in which plants near the trap experience an increase in feeding and injury. Research has demonstrated that plants in residential landscapes infested with Japanese beetle experience substantially more feeding injury when one or more traps are deployed, compared with similar landscapes in the absence of traps. Although no specific trapping thresholds have been established for Japanese beetle management in home gardens, traps that capture a large quantity of beetles in a short period of time indicate that an infestation is present. In such instances, further management is warranted.
In addition to trapping, plants can be inspected for feeding injury and the presence of adults in the summer. It is highly recommended that plant inspections be done in areas where an infestation was present the previous year.
Cultural control
Maintain healthy plants with proper irrigation and fertilization. Japanese beetle tends to avoid certain plants such as lilac, forsythia, dogwood, magnolia, and American holly; therefore, incorporating these plants in or around vegetable gardens will provide some additional protection. Intercropping During the warmest part of the day when beetles are most active, adults can be handpicked and placed in a jar of soapy water.
Hand picking
Hand picking beetles can often be effectively employed in small plantings to help reduce feeding injuries caused by Japanese beetles. The beetles can be easily picked or dislodged from plants or can be removed by shaking infested plants over a collecting container in the early morning when temperatures are cool. To be effective, it is recommended that handpicking be performed daily. Since beetle flights peak at midday and plants are colonized in the afternoon, hand picking beetles in the evening will further optimize this approach by maximizing the number of beetles removed. Furthermore, removing beetles in the evening reduces overnight feeding, resulting in decreased emission of plant volatiles that would otherwise attract more beetles to the injured plant.
Biological control
Two species of parasitoid wasp, Tiphia vernalis and Tiphia popilliavora (Hymenoptera: Tiphiidae), and one parasitoid fly, Istocheta aldrichi (Diptera: Tachinidae), have become established in the northeastern United States. However, these parasitoids are not commercially available for purchase and do not provide reliable site-specific control of Japanese beetles.
Foliar spray applications of Bacillus thuringiensis galleriae (Btg) may suppress feeding of Japanese beetles but can be toxic toward lepidopteran species. Therefore, Btg should not be applied in landscapes with lepidopteran host plants, especially those of threatened or endangered species such as the monarch butterfly, Danaus plexippus (Lepidoptera: Danaidae).
Chemical control
Many of the chemical controls for Japanese beetle work to reduce the densities of eggs and larvae in turfgrass. While some insecticides can help control adult Japanese beetles, very few of these are approved for organic pest control, and there is a lot of variation among insecticides with respect to the length of time they persist, what plants they can be used on, whether they act systemically, and their toxicity towards beneficial insects, most notably pollinators. Insecticides that are less toxic to pollinators and persist for only a short period of time can be used on flowering plants when applications are made in the early morning or dusk when bees are not actively visiting plants. While some insecticides are less toxic to pollinators, it is important to note that organic insecticides are not necessarily safer for beneficial insects.
Generally, insecticides should only be used as a last resort when pest densities reach damaging levels and there are no alternative control options. Given the high dispersal activity and wide variety of plant hosts, Japanese beetles will often reinfest areas treated with insecticides. In such instances, multiple applications may be needed, which can result in outbreaks of secondary pests such as mites, whiteflies, and scales, depending on the insecticide. Defoliation can also be reduced with treatments of pyrethrin, but this insecticide should not be applied during flower periods to minimize effects on pollinators.
Azadirachtin is derived from neem oil and acts as a feeding deterrent, and applications have been shown to deter feeding of Japanese beetles. However, beetles tend to habituate after repeated exposure, reducing the effectiveness of deterrents. Saponins are a class of plant defense compound that are especially abundant in Medicago spp. such as alfalfa (M. sativa). Laboratory and field research suggests that these compounds display repellent properties against Japanese beetles and may be incorporated into existing management programs for Japanese beetle.
References
Alston, D., and C. Stanley. 2010. Japanese Beetle. Utah State University – Extension. Available https://extension.usu.edu/pests/uppdl/files/factsheet/japanese-beetle-10.pdf
Althoff, E., and K. Rice. 2022. Japanese Beetle (Coleoptera: Scarabaeidae) Invasion of North America: History, Ecology, and Management. Journal of Integrated Pest Management. 13(1): 1-11. Available https://academic.oup.com/jipm/article/13/1/2/6503655
Cranshaw, W. 2018. Japanese Beetle. Colorado State University – Extension. Available https://cmg.extension.colostate.edu/wp-content/uploads/sites/6/2021/04/Japanese-Beetle-factsheet.pdf
Hahn, J. 2022. Japanese beetles in yards and gardens. University of Minnesota – Extension. Available https://extension.umn.edu/yard-and-garden-insects/japanese-beetles#preventive-insecticides-1592862
Iovinella et al. 2023. Antifeedant and insecticidal effects of alfalfa saponins in the management of the Japanese beetle Popillia japonica. Journal of Applied Entomology. 147: 651-660. Available https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/jen.13153
Pinero, J., and J. Quinn. 2018. Organic Management Options for the Japanese Beetle at Home Gardens. University of Missouri – Integrated Pest Management. Available https://ipm.missouri.edu/MEG/2018/1/organic_management_japanese_beetle/
Redmond, C., L. Wallis, M. Geis, R. Williamson, and D. Potter. 2019. Strengths and limitations of Bacillus thuringiensis galleriae for managing Japanese beetle (Popillia japonica) adults and grubs with caveats for cross-order activity to monarch butterfly (Danaus plexippus) larvae. Pest Management Science. 76: 472-479. Available https://onlinelibrary.wiley.com/doi/epdf/10.1002/ps.5532
Switzer, P., and R. Cumming. 2014. Effectiveness of Hand Removal for Small-Scale Management of Japanese Beetles (Coleoptera: Scarabaeidae). Journal of Economic Entomology. 107(1): 293-298.
USDA. 2015. Managing the Japanese Beetle: A Homeowner’s Handbook. United States Department of Agriculture – Animal Plant and Health Inspection Service. Available https://www.aphis.usda.gov/plant-pests-diseases/japanese-beetle