The Japanese beetle, Popillia japonica, is an invasive insect first detected in the United States in 1916 and has become a highly destructive pest. This insect poses a significant threat to both agricultural crops and ornamental landscapes due to its exceptionally broad diet. The beetle’s life cycle includes two distinct stages—adult and larval—each causing different forms of damage by feeding on entirely different parts of plants.
Feeding Habits and Damage Identification
Adult Japanese beetles begin to emerge from the soil in late June and feed actively through August, targeting over 300 plant species during this period. The beetles use their chewing mouthparts to consume the soft tissue of the leaves, while consistently avoiding the tougher, structural veins.
This selective feeding behavior results in a distinctive pattern known as “skeletonization,” where the leaf is reduced to a lace-like network of veins. The damaged leaves soon turn brown and wither, which can lead to significant defoliation of trees and shrubs when large populations of beetles are present. Adult beetles also aggregate on plants, often attracted by scents released from previously damaged foliage, resulting in concentrated feeding that can quickly destroy flowers and ripening fruit.
Preferred Host Plants of Adult Beetles
The adult Japanese beetle is an opportunistic feeder, but it shows a strong preference for plants that are easily digestible and have soft, tender foliage. The most heavily favored host plants can be grouped into categories based on their role in the landscape.
Ornamental Plants
Roses are one of the most famous targets, with the beetles often congregating on the petals and leaves, rapidly skeletonizing the foliage and destroying the blooms. Other flowering shrubs and perennials with tender leaves are also frequently attacked, including hibiscus, cannas, and purple coneflower (Echinacea spp.). The damage to these decorative plants is often the first sign of an infestation that homeowners notice.
Shade Trees
Several popular shade and landscape trees are highly susceptible to adult Japanese beetle feeding. American and little-leaf linden trees (Tilia spp.) are major hosts, often suffering extensive skeletonization across their entire canopy. Birch trees, especially susceptible varieties, frequently sustain heavy damage, which can weaken them and predispose them to other secondary pests. Other favored woody plants include crabapples and Japanese maples, particularly those with softer leaf textures.
Fruit Crops
The beetles’ appetite extends significantly into agricultural settings, where they can cause economic damage to fruit-bearing plants. Grapevines are a primary target, with beetles consuming the leaf tissue between the veins and occasionally feeding directly on the fruit clusters. Various stone fruits are also susceptible, including the leaves and fruit of cherry, peach, and plum trees. Small fruits like raspberries and blackberries are likewise attractive to the adults, which can cause severe defoliation and fruit damage during the summer feeding period.
The Diet of Japanese Beetle Grubs
The larval stage of the Japanese beetle, commonly known as a white grub, has a fundamentally different diet than the adult, living entirely below the soil surface. These C-shaped larvae primarily feed on the fine roots of grasses, making turfgrass the main target of this developmental stage. They show a strong preference for the roots of high-quality turf, such as Kentucky bluegrass, perennial ryegrass, and tall fescue.
Grubs are present in the soil for about 10 months of the year, with the most significant root-feeding occurring during the late summer and early fall as they grow larger. When grub populations are high, their consumption of roots can severely limit the grass’s ability to absorb water and nutrients.
This results in localized patches of turf that turn brown and die, often mistaken for drought stress. A tell-tale sign of severe grub damage is that the affected turf can be easily lifted and rolled back like a piece of loose carpet because the roots holding the sod to the soil have been completely severed. This root damage not only kills the grass but also attracts digging animals, such as skunks and raccoons, which tear up the lawn to feed on the grubs, causing further destruction. The feeding of grubs is a significant concern for both homeowners and golf course managers maintaining large areas of manicured lawn.
Plants They Avoid
While the adult Japanese beetle feeds on a vast array of plants, there are many species that they reliably avoid, which provides practical options for gardeners in affected areas. These avoided plants often possess physical characteristics, like tough or leathery leaves, or chemical properties that make them unpalatable to the beetles.
Many common evergreens are rarely attacked due to their needle-like or tough foliage, including:
- Arborvitae
- Hemlock
- Pines
- Junipers
Several deciduous trees and shrubs are also relatively safe from feeding, such as:
- Boxwood
- Magnolia
- Lilac
- Flowering dogwood
Certain maple varieties, particularly red maple and silver maple, are generally considered resistant, in contrast to the heavily damaged Japanese and Norway maples.