Damage Caused by Japanese Beetle
Natural Environment
The JB feeds on a broad range of plants, so if it became permanently established in California it would pose a serious threat to some of our native plants, including some of California’s threatened and endangered species that are related to one or more known host plants. A discussion of these species follows, and those recognized nationally are denoted as federally endangered (FE) or federally threatened (FT), while species on the California lists are state endangered (SE) or state threatened (ST).
Members of the rose family (Rosaceae) are commonly attacked by JB. Roses (Rosa spp.) are preferred hosts. Small-leaved rose (Rosa minutifolia; SE) occurs only in San Diego County in the United States. The Mt. Shasta snow-wreath (Neviusia cliftonii; Rosaceae) is found only in the Mt Shasta region and is closely related to Kerria japonica, a plant that is a known host for JB. Hickman’s cinquefoil (Potentilla hickmanii; FE; SE) is an endangered plant of the Central Coast of California that is in the rose family.
A range of grasses (Poaceae) are attacked by JB, especially in its larval stage. Rare grasses in California that might be attacked by JB include Napa bluegrass (Poa napensis; FE; SE) and Sonoma alopecurus (Alopecurus aequalis ssp. sonomensis; FE). In addition, California is the only home of a group of grasses endemic to vernal pools including such species as hairy Orcutt grass (Orcuttia pilosa; FE; SE) and Tuctoria mucronata (Solano grass; FE; SE).
The mustards (Brassica spp.) are attacked by JB. California is home to many rare, endemic members of the mustard family (Brassicaceae). Examples include California jewelflower (Caulanthus californicus; FE; CE), Metcalf Canyon jewelflower (Streptanthus albidus; FE), and Mt Hermon wallflower (Erysimum teretifolium; FE; CE).
The mallow family (Malvaceae) has many members that are attacked by JB. Examples of California genera containing rare species in this group include checkermallows (e.g., bird‐foot checkerbloom, Sidalcea pedata [FE; CE] and Keck’s checkermallow, Sidalcea keckii [FE]) and California hibiscus (Hibiscus lasiocarpus var. occidentalis).
JBs attack several genera of the legume family (Fabaceae), including theclovers (Trifolium spp.). Rare clovers in California include showy Rancheria clover (Trifolium amoenum; FE)andMonterey clover(Trifolium trichocalyx; FE; SE). The legume family also includes lupines, the larval food plants of several endangered invertebrates. Lupines, especially L. arboreus, are the larval food plant of the Mission blue butterfly (Plebejus icarioides missionensis; FE) and Boisduval’s blue butterfly (Icaricia icarioides; FE).
Several genera of the knotweed family (Polygonaceae) are attacked by JB. In California, Hickman’s knotweed (Polygonum hickmanii; FE; SE) and Ione buckwheat (Eriogonum apricum spp. apricum; FE; SE) are examples in Polygonaceae of rare species that potentially could be attacked by JB. The genus Eriogonum contains several species that are the obligate host plants of endangered invertebrates such as El Segundo blue butterfly (Euphilotes battoides allyni; FE), Smith's blue butterfly (Euphilotes enoptes smithi; FE), and Lange's metalmark butterfly (Apodemia mormo langei; FE; SE).
The exceedingly large daisy family (Asteraceae) contains several known hosts of JB such as sunflower (Helianthus annuus) and horseweed (Erigeron canadensis). Closely related species of concern in California include Algodones Dunes sunflower (Helianthus niveus ssp. tephrodes; FE; SE) and Parish's daisy (Erigeron parishii; FT).