Japanese Beetle, Popillia japonica
Order: Coleoptera
Family: Scarabidae
Description
The adult Japanese beetle (order: Coleoptera, family: Scarabaeidae) has an oval body and is about 15 mm (3/5 inch) in length. It is generally metallic green with coppery brown wing covers, which 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. Japanese beetle larvae are white grubs that feed on the roots of grasses. 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. The eggs of Japanese beetle can be cylindrical or spherical.
Quick Facts
- The Japanese beetle is an invasive species in the United States. It is currently established in 28 states and is continuing to expand its range. It was first detected in Colorado in 1997.
- Japanese beetle adults feed on fruit, foliage, and flowers of over 300 plant species. The larvae primarily feed on grass roots.
- Some examples of ornamental plants susceptible to attack by Japanese beetle include various conifers, roses (Rosa spp.), crabapple (Malus spp.), linden (Tilia spp.), maple (Acer spp.), crapemyrtle (Lagerstroemia spp.), and elm (Ulmus spp.).
- Adults are best controlled by handpicking or by the use of certain insecticide sprays
- Japanese beetle traps can capture many adults but have never been shown to reduce damage to nearby plants
- Japanese beetle larvae can be controlled with certain insecticides or by insect parasitic nematodes
Japanese beetles have been one of the key insect pests of both turfgrass and landscape plants in the eastern US and now in the western U.S. These beetles cause significant defoliation and damage to leaves and flowers of many plants. Image credit: USDA ARS Photo Unit, USDA Agricultural Research Service, Bugwood.org
Japanese beetles feeding. Image credit: Ada Szczepaniec, Colorado State University, Fort Collins, CO
White grubs (larvae) of the Japanese beetle. Image credit: David Shetlar, Ohio State University
Japanese beetles mating. Image credit: Ada Szczepaniec, Colorado State University, Fort Collins, CO
Japanese beetle parasitized by the fly, I. aldrichi. Note the presence of eggs (arrow) on the thorax. Image credit: Whitney Cranshaw. Colorado State University.
Life history and habits
Japanese beetles begin to emerge from the soil in early June and are usually most abundant from late June through early August. Adults can attack over 300 plant species and 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 after feeding for 4-8 weeks. The pupal stage can last anywhere from one week to 17 days. One generation is produced per year.
Injury
Japanese beetles can cause injury to plants in both the adult and larval stages. However, the type of injury caused by adults and larvae are very different. Injury by the adults is more obvious and is usually the primary concern. Adults feed on leaves, buds, and flowers of many commonly grown vegetable and landscape plants. Feeding is usually restricted to the tender tissues between the larger leaf veins, which results in a characteristic skeletonizing type of injury. More generalized feeding occurs on softer tissues such as flower petals. Rose flowers are particularly susceptible to Japanese beetle injury.
Japanese beetle larvae feed on the roots of turf grasses, limiting the plant’s ability to acquire water. It is likely there will be increasing turfgrass damage in areas where this species becomes established, adding to the damage done by native white grubs present in Colorado turfgrass (e.g., masked chafers, May/June beetles).
Trapping
Correct timing and application protocols are necessary for effective chemical control of Japanese beetle. 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. It is important to note that, under high populations, 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 beetles experience substantially more feeding injury when one or more traps are deployed, compared with similar landscapes in the absence of traps.
Cultural control
When beetle populations are low, roses with yellow flowers are more susceptible to feeding injuries than roses with red flowers. In addition, removing blooms from rose plants during peak beetle flights can reduce feeding injury. Two species of crabapple, M. hupehensis and M. baccata, are less susceptible to defoliation than other crabapple varieties. Between these two species, beetles prefer to feed on M. hupehensis over M. baccata. Of the linden trees, T. tomentosa is more resistant to defoliation when beetle populations are low. Regarding maples, crapemyrtles, and elms, research suggests that there is no difference between the susceptibility of green- and red- leafed cultivars. However, there are cultivars with differing plant physiology with respect to plant odors, foliar secondary compounds, and leaf pubescence, that are more resistant to Japanese beetles.
Hand picking
Hand picking beetles can often be effectively employed in small plantings to help reduce feeding injuries of Japanese beetles. Such feeding injuries induce the emission of plant volatiles that attract more foraging adults to the injured plant, and one major benefit of hand picking is that it reduces the emission of these volatiles. The beetles can be easily picked or dislodged from plants or can be removed by shaking infested plants over a collecting container in 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.
Biological control
Natural enemies of Japanese beetle include predators and parasitoids. Ants feed on the eggs of Japanese beetle, while birds and mammals feed on adults and larvae. Several parasitoid species, Tiphia vernalis, T. popilliavora, and Istocheta aldrichi, are native to Asia and Australia have been released in the United States in the east coast and as far west as Missouri. The Tiphia spp. are wasps that lay eggs on the larvae of Japanese beetles, while I. aldrichi is a fly that attacks adults.
Chemical control
Some insecticides commonly used for managing Japanese beetle include pyrethroids, organophosphates, carbamates, neonicotinoids, and anthranilic diamides. These different insecticides vary considerably in features such as how long they can persist and control beetles, what plants they can be applied to, whether they move systemically in the plant, and their degree of hazard to beneficial insects, notably pollinators. Insecticides that are highly toxic to bees and can persist long enough to kill insects for days are hazardous to foraging pollinators. Some insecticides, which are less toxic to bees or persist for only a short period, can be used on flowering plants if applications are made during early morning or dusk–when bees are not active and visiting plants. A couple of insecticides do not have restrictions for use on plants in bloom because they have very little, if any, toxicity to bees.
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. Certain anthranilic diamides can be used to reduce defoliation of woody ornamentals and have low toxicity toward bees. 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 on Tilia cordata, a species of linden, up to 14 days after treatment. However, its effectiveness may be reduced after multiple applications since Japanese beetles tend to habituate after repeated exposure. 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. Foliar spray applications of Bacillus thuringiensis galleriae (Btg) may also 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.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
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
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
Redmond, C., L. Wallis, M. Geis, R. Williamson, and D. Potter. 2019. Strengths and limitations of 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.