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Invasion of Beetles

False Japanese Beetle (Strigoderma arbicola)

University of Minnesota Extension, Stearns County News
June 25, 2014       
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties

Invasion of Beetles
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (6/25/14) — The season of False Japanese Beetles, Strigoderma arbicola, has started.  False Japanese beetles are a member of the Junebug family and are native to Minnesota and often called spring rose beetles.  In addition to the False Japanese Beetle, potential recent discovery of the Japanese Beetle, Popillia japonica, have been detected in Stearns County.  Both beetles are destructive to yards and gardens.

False Japanese Beetles are often found in grassy, sandy areas especially in Anoka, Sherburne, Benton, and Stearns counties. These pests are about 7/16 inch long and the beetle’s thorax and head are a dull metallic green while its wing covers are a brown.  False Japanese Beetles feed, mate and lay eggs in the spring and generally disappear from the garden by the end of July.

Damage can be significant; the adults feed on blossoms but may also feed on the foliage and fruit of the plant.  The False Japanese Beetle seems to prefer roses, specifically light colored blossoms.  They will also cause damage to blackberries, clover, coreopsis, hollyhock, iris, lilies, peonies, honeysuckle, and a variety of vegetable plants including beans, cantaloupe, corn, cucumbers, and peas.

Management of the beetles can include both physical removal or restraints, or chemical treatment.  If the concentration in your yard is minimal, simply remove with gloves and crush, or put into a cup of soapy water. Placing a light fabric cover such as a cheese cloth over the plants can also prevent flower damage. Chemical sprays that contain carbaryl (Sevin) or permethrin (Eight) can be effective, however because the beetles are very mobile and strong flyers, repeat inspection and treatment may be necessary. Gardeners may choose to focus on protecting and treatment of high value plants rather than using repeat insecticides. Caution should be used when using any insecticide; read the label thoroughly before use and treat only plants listed on the label. To minimize harm to beneficial insects such as bees, apply during early morning or late night when bee activity is minimal.

Japanese Beetles are an introduced species to Minnesota and cause serious problems to turf and ornamental plants. They were first introduced to North America in 1916, and have continued to expand in range.  Japanese Beetles are about one-half inch in length and one-quarter inch in width; their thorax and head are a bright green metallic with copper wing covers.  The distinct characteristic to differentiate them from the native False Japanese Beetle are the five small tufts of white hair along the sides of the body with an additional two white tufts at the rear of the beetle. 

Japanese Beetle larvae (grubs) are “C” shaped and are destructive to the roots of turfgrass, feeding August through October. The adult beetles feed on over 300 species of plants and have even caused damage to some tree species such as maple, oak, birch, and mountain ash to name a few.  Adults become active in June and persist through August, feeding on the leaf tissue between the leaf veins. Japanese Beetles typically begin feeding at the top of the plant and work their way down as the foliage is consumed. Approximate life span of the beetles is 60 days, in which feeding can cause severe damage and the females lay eggs for the life cycle to continue.

Management of the Japanese Beetle requires proper timing.  Insecticides to exterminate the grubs should be applied from May through mid-June, to control overwintered grubs as they start to feed. By mid-July the pupae are typically too large to be impacted by these insecticides.  By the end of June/early July the adults emerge to feed on plants, and then mate, and lay eggs.  Adult control includes physical removal when populations are low.  Be aware, the presence of beetles attracts more beetles. Carbaryl, acephate, pyrethrings, and pyrethroids can be used as a foliar contact spray to kill adults immediately. Grub control can be applied mid-July through the end of September to control the grubs hatched from the eggs laid in July. All products should be used with caution, and according to the label.

Homeowners should be watchful of both the False Japanese Beetle and the Japanese Beetle, and if discovered begin management to help protect your yards.  For more information, including trade names of the insecticides visit





Beth Berlin
Extension Educator, Horticulture
(320) 255-6169
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