Asiatic Garden Beetle
Order: Coleoptera
Family: Scarabaeidae
Maladera castanea
Overview
A native of China and Japan, where it is not an important pest, the Asiatic garden beetle (AGB), Maladera castanea, has been known in the Northeast since the 1920s (established in New Jersey by approximately 1921). In Massachusetts, the AGB is commonly seen in the Connecticut River Valley and throughout southeastern Massachusetts, particularly on Cape Cod, but is likely widespread. AGB feeds on many plants in the landscape, causing widespread damage on both foliage and the blossoms of its hosts. It goes undetected perhaps more often than other beetles because it feeds nocturnally.
Host Plants
Over 100 plants are potential hosts for the Asiatic garden beetle. This includes many fruit, vegetable, perennial and annual flowering plants, trees and shrubs, as well as weeds and grasses (preferring longer, overgrown areas to short, well-maintained turf). As an adult, this scarab beetle will feed on both agricultural and horticultural species, including beet, boxelder, carrot, cherry, eggplant, peach, pepper, strawberry, turnip, viburnum, and flowers such as aster, chrysanthemum, dahlias, goldenrod, and roses. As an immature grub, Asiatic garden beetle prefers to feed on the roots of ornamentals, garden plants, and blueberries, especially when found in or near weedy areas. While grubs do not historically prefer turf as a host, they will utilize it if necessary.
Identification/Life Cycle
In the Northeast there is one generation of Asiatic garden beetles per year. In warmer climates, such as parts of Florida where this insect has also been introduced, it is possible that multiple generations may occur per year. AGB overwinters 8-17 inches beneath the soil as an immature larva (grub). This is somewhat deeper than other, similar grubs. Larvae then pupate in an earthen cell the following May/June (late-June in MA), and emerge from the soil at night in late-June/July as adults. Pupae are white or tan in color and approximately 5/16 - 3/8 of an inch in length. Adult AGB’s shape is similar to the Japanese beetle (Popillia japonica), though slightly smaller. (They have been described as having a similar size and shape to a coffee bean.) They have chestnut brown, lightly iridescent wings, and their abdomen extends slightly beyond their wing covers. AGB adults feed at night on leaves and flowers throughout the remaining summer months and are most abundant in July and August, but may be present until October. (During the day, adult beetles hide in the soil until dusk when they emerge again to feed.) When temperatures are above 70 degrees Fahrenheit, adult beetles fly from host to host; below 70 degrees Fahrenheit, they crawl from host to host. AGB tends to feed close to the ground. Asiatic garden beetle adults are also highly attracted to light when active at night. They may become numerous at doors, windows, or wherever there is a bright light. During this time AGB is also mating. Female AGBs lay eggs 1-2 inches deep in the soil in clusters of 3-15 eggs, glued together with a gelatinous secretion. In a single season, a single female lays up to 60 eggs over the course of several weeks. The eggs absorb water from the surrounding soil, becoming spherical, then hatch about ten days later into young grubs. Young larvae are approximately 1/16th of an inch long with light brown head capsules, six legs, and C-shaped. Larvae also possess a branched anal opening (slit) and a single row of curved spines that extends across the underside of the last abdominal segment. These dig to the soil surface and feed on roots and other organic material until October, when they tunnel deeper in the soil to overwinter. Mature larvae are white or tan and ⅜- ½ inch long.
Damage
The Asiatic garden beetle is often considered to be a minor pest in the immature stage, with the feeding damage caused by larvae (grubs) less significant than that of the adult beetles or other grubs of similar species (ex. Japanese beetles, Popillia japonica). However, this is not always the case. When populations are very large, Asiatic garden beetle grubs can potentially cause noticeable damage as they are able to burrow deeper to feed than many other similar grub species. Larvae are often not uniformly distributed through a single landscape. They often prefer weedy, grassy areas but may also be found in flower beds and vegetable gardens. Moist, loamy to sandy loam soils are preferred. Orange hawkweed (Hieracium spp.) is a favorite host for Asiatic garden beetle larvae, with records of up to 100 grubs per square foot in nearby soils.
Adult AGB's cause damage by eating the leaves and flowers of their host plants. Heavy infestations can lead to complete defoliation except for leaf midribs, especially on preferred host species such as butterfly bush, rose, dahlia, aster, and chrysanthemum. Adult beetles begin to feed first at the margins of the leaves. Adult beetle feeding creates ragged damage to host plant leaves, not leaf skeletonization like Japanese beetles. Eventually, foliage and flowers may be completely destroyed.
Monitoring
Asiatic garden beetle adults are difficult to observe because they feed at night and conceal themselves in ground litter or soils during the day. However, they are attracted to light, making them a prime target for light traps. At home, a light trap may be fashioned out of an outdoor-safe light bulb suspended above a flat pan of soapy water. Because AGB tend to feed closer to the ground, the water should be placed on the ground with the lightbulb 6 inches above it. Adult beetles attracted to the light will become trapped in the soapy water and drown. This technique can be used to monitor for the presence of this insect if it is a suspected cause of damage on high-value host plants, however it is unknown whether or not this will effectively reduce damaging populations of the Asiatic garden beetle adults. It may also be important to place traps away from favored host plants to avoid accidentally attracting this insect to suitable hosts.
Management Strategies:
Asiatic garden beetles (particularly the immature grub stage) may not cause enough damage to require action, (especially chemical use); however, in the case of a severe or damaging infestation, see strategies below.
Cultural/Mechanical Management:
Handpicking AGB at night can reduce small populations. Adult beetles may drop to the ground when disturbed, so capturing them in a bowl of soapy water when hand collecting (place the bowl beneath the infested foliage before disturbing the beetles) may be useful. Use a light trap as described above to draw AGB towards a pan of soapy water. Fabric covers in ornamental and vegetable garden beds may also help deter adults, unless they are already present in the soil beneath the plants. Sanitation in the fall (removing weeds and tall grasses) may help deter AGB populations the next season.)
Biological Control/Natural Enemies:
There are no known biological control measures or effective natural enemies for the Asiatic garden beetle at this time.
Chemical Management:
In lawns and other turf areas, the Asiatic garden beetle grub (immature) may be managed as with other white grubs found in turf. For recommendations with turf management, see UMass Extension's Professional Turf IPM Guide under "White Grubs".
Asiatic garden beetle adults are not known to be resistant to insecticides, and are able to be managed with products labelled for this use. Several insecticides are labelled for management of this insect on woody ornamentals. Read and follow all label directions carefully.
Active ingredients labelled for use against adult Asiatic garden beetles in Massachusetts include but are not limited to: bifenthrin, clothianidin*, cyantraniliprole, cyfluthrin, dinotefuran*, imidacloprid*, and lambda-cyhalothrin.
Always read the entire label of any pesticide product before use. Ensure that you are using it in a manner consistent with the labeling. The label is the law. No product should be used in a manner that is contrary to its label. Read and follow all label instructions for safety and proper use. Make sure that the product you select is labelled for use against the pest you wish to manage, on the site to which it will be applied. Do not apply systemic insecticides, such as neonicotinoids, to plants in bloom. *Neonicotinoid insecticides cannot be applied to trees or shrubs in Massachusetts except by an individual with the proper licensure or certification from the MA Department of Agricultural Resources.
