Japanese Beetle Fact Sheet No. 5.601 Insect Series|Home and Garden by W. Cranshaw* For close to a century, the Japanese Quick Facts beetle (Popillia japonica) has been one of the most seriously damaging insect • Japanese beetle adults chew pests of both turfgrass and landscape flower blossoms and leaves plants over a broad area of the eastern of many commonly grown US. Recently, there have become a few plants. permanent, reproducing populations of this insect in some communities • Japanese beetle larvae are a along the Front Range of Colorado. At type of white grub that feeds some of these sites high numbers of on the roots of grasses. Japanese beetles now regularly occur • Adults are best controlled and adult beetles are causing significant by handpicking or by use of damage to leaves and flowers of many Figure 2. Japanese beetle damage to leaves of grape. susceptible landscape plants. certain insecticide sprays. body with a dark head and the legs on • Japanese beetle traps can the thorax are well developed. Normally capture many adults have Description of the the body curves into a “C-shape”. never been shown to reduce Japanese Beetle These features are also typical of damage to nearby plants. The adult Japanese beetle has an other white grubs found in association oval form is about 7/16-inch in length. It with turfgrass in Colorado, such as • Japanese beetle larvae can is generally metallic green with coppery- masked chafers and May/June beetles. be controlled with certain brown wing covers, which do not quite (Extension fact sheet 5.516, Billbugs insecticides or by insect and White Grubs discusses white grubs cover the tip of the abdomen. Along the parasitic nematodes. sides are five patches of whitish hairs. of turfgrass in more detail.) Japanese The antennae are clubbed at the end beetle larvae are slightly smaller than and may spread to a fan-like form. these other species when full grown but Japanese beetle larvae are a type they are best distinguished by closely of white grub that feeds on the roots examining the pattern of hairs on the of grasses. They have a creamy white hind end of the abdomen (‘rastral pattern’), which forms a distinctive V-shape. Japanese Beetle Damage Japanese beetle can be damaging to plants in both the adult and larval stages. However the type of injuries produced by adults and larvae are very different. Injury by the adults is more obvious and is usually the primary concern in Figure 1. Rose blossoms are one of the most Colorado. Adults feed on leaves, buds © Colorado State University highly favored foods of Japanese beetles. and flowers of many common garden Extension. 5/07. Revised 3/18. and landscape plants (Table 1). On extension.colostate.edu leaves feeding is usually restricted to *W. Cranshaw Colorado State University Extension the softer tissues between the larger leaf entomology specialist, and professor, bioagricultural veins, which results in a characteristic sciences and pest management. 3/2018 Table 1. Some plants that are most commonly damaged by Japanese beetle adults. Virginia creeper* Grape Rose** Linden* Silver lace (Polygonum aubertii)** Gaura** Rose of Sharon** Hollyhock* Raspberry* Crabapples (some) Japanese maple Peking cotoneaster Beans (edamame) Basil (green) Figure 3. White grubs (larvae) of the Japanese beetle. Photograph courtesy of David Shetlar, Plants that are in flower during part of the time the Ohio State University. when Japanese beetle adult are present are indicated by a single asterisk *. Plants that may be blooming the entire time when Japanese beetles are present on the plant are indicated by Figure 6.. White grubs feed on the roots of two asterisks **. grasses. Photograph courtesy of David Shetlar, the Ohio State University. established, adding to the damage done by native white grubs present symptoms of injury may be present in Colorado turfgrass (e.g., masked at this time, with damaged grass chafers, May/June beetles). appearing drought stressed. Larvae continue to feed until soil o Japanese Beetle Life temperatures drop to about 60 F at Figure 4. The rastral pattern that is distinctive which time the larvae move deeper for white grubs of the Japanese beetle. The History in the soil where they remain through rastral pattern is located on the underside of Japanese beetle has a one year winter. All activity ceases when soil the tip of the abdomen. Photograph courtesy of o David Shetlar, the Ohio State University. life cycle. Adults may begin to temperatures drop below 50 F. Activity emerge from the soil in early June and resumes as soils warm in spring and, are usually most abundant in early after a feeding period of about 4-6 summer - from late June through early weeks, the larvae form an earthen cell August. However, some adults may be and pupate. A few weeks later the found into September. pupal stage is completed and the new As adults, Japanese beetles can adults emerge. be found feeding and mating on foliage and flowers of their host plants. Periodically, mated females will move Control of Adult in late afternoon to areas of turfgrass to Japanese Beetles lay eggs. They seek areas where soil is Japanese Beetle Trapping. Traps are Figure 5. Japanese beetles that feed on leaves suitably moist and then dig 2-3 inches produce a characteristic skeletonizing pattern. available that can capture Japanese where they will lay a small cluster of beetle adults. These typically have a feeding pattern known and described eggs among the plant roots. They vane of yellow panels at the top with as “skeletonizing”. More generalized subsequently emerge and will resume a funnel underneath into which the ragged feeding occurs on softer feeding on host plants, returning to beetles fall after impacting the panels. tissues, notably flower petals; rose turfgrass later to lay more eggs. A total A lure of floral-based compounds is flowers are particularly susceptible of 40-60 eggs may be laid by each used that is highly attractive to adults. to Japanese beetle injury. Damage Japanese beetle female during the on individual plants may be patchy, course of her 4-8 week life span. concentrated where aggregations of Upon hatching from the eggs feeding beetles occur. the grubs (larvae) seek out nearby Japanese beetle larvae feed on plant roots and feed. During the roots of grasses, in a manner similar time Japanese beetles are in the to other turf damaging white grubs. egg and earliest grub stage they are These injuries produce root pruning quite sensitive to drying and may that limit the plant’s ability to acquire die if soils temporarily dry during Figure 7.. The life stages of the Japanese water. Damaged areas of turfgrass are this period. Later stage larvae are beetle. From left to right: egg, larva (stage I), more susceptible to water stresses and less sensitive to drying. Japanese larva (stage II), larva (stage III), pupa, adult. Photograph courtesy of David Shetlar, the Ohio severely pruned roots can lead to plant beetle larvae become nearly full-size State University. death by drought. It is likely that there by early September and their rapid will be increasing turfgrass damage development during late summer can in areas where this species becomes cause extensive root pruning. Surface can be particularly productive. The Some insecticides, which are less regular removal of beetles prevents toxic to bees or persist for only a the feeding damage produced by short period, can be used on plants the beetles, which can reduce the that are in flower if applications are production of chemicals produced by made during times of the day–early wounded plants that are attractive to morning, dusk–when bees are not the adult beetles. active and visiting plants. Examples Insecticides.There are several include pyrethrins, azadirachtin, and insecticides that can be used to help acetamiprid. control damage by adult Japanese A couple of insecticides do not have beetles (Table 2). These different restrictions for use on plants in bloom insecticides vary considerably in because they have very little, if any, features such as how long they can toxicity to bees. These include Bacillus persist and control beetles, what thuringiensis var. galleriae (beetleJUS, plants they can be used on, whether beetleGONE!) and chlorantraniliprole they move systemically in the plant, (Acelepryn). At present (2018) the and their hazard to desirable insects, former are only available through mail notably pollinators. order and Acelepryn is only marketed for commercial/agricultural uses. Control of Japanese Beetle Grubs in Lawns Japanese beetle grubs can damage Figure 8. Typical trap used to capture adults of turfgrass in the same manner as other the Japanese beetle. turfgrass white grubs. (See Extension Large numbers of adult beetles Fact Sheet 5.516, Billbugs and White can be captured in these traps and Grubs). Some cultural practices can they are useful for detecting the limit damage and applied chemical or presence of Japanese beetle for biological controls may also be useful. survey purposes. The traps also have However, control of Japanese beetle some value in control where Japanese larvae in a yard will have very little, if beetles are restricted to a very limited any, effect on the number of Japanese location; mass beetle trapping was beetle adults feeding on trees, shrubs a component of the Japanese beetle and garden plants. The insect is highly eradication in Palisade, CO. mobile so that problems with adult Unfortunately, Japanese beetle beetles typically involve insects that traps are ineffective for control where have moved a considerable distance. Japanese beetle is well established Cultural Controls. Mowing can affect over a large area, common now in the susceptibility of lawns to grub many Front Range locations.