Last summer, an invasive insect from the eastern half of the United States was found in the Treasure Valley, brought into Idaho and surrounding states. The insects were Japanese Beetles (Popillia japonica), probably the most destructive insect of urban landscape plants in the eastern half of our Country. Less than 150 insects were found here but that was enough to cause alarm for the Idaho Department of Agriculture and the Idaho Nursery industry.

The insects were scattered but the majority of these insects were found in the east end of Boise. If you’ve been through that area you may have wondered about the bright yellow cone shaped traps, as there are hundreds of them. Homeowners have given the Department of Agriculture permission to treat the area where the highest concentration of those insects were found.

Japanese Beetle

People who have lived in places that have Japanese Beetles know the headache they can be. Here’s some Japanese Beetle biology. The adult insect is a brilliant metallic green. The wing covers are a coppery color and there are five tufts of white hair along each side. The white hairs are an important diagnostic feature. The adult insects are about 1/2 inch long and live for about 30-45 days. The larvae, found in turf, are typical white grubs that curl into a ‘C’ shape when disturbed. They have three pairs of legs and grow to be about 1-1/4 inch long.


The adult insects begin to feed on plants and laying eggs shortly after they emerge from the ground, normally for four to six weeks beginning in June. The females leave plants in the afternoon and deposit one to five eggs two to three inches deep in the soil of a grassy area. They can lay as many as 40 to 60 eggs during their lifetime. The larvae feed on grass roots causing damage similar to billbug damage. Bluegrass is a preferred variety but all grasses are susceptible. The grubs overwinter in the soil, and can survive in almost any soil plants live in.

Japanese BeetleThe adult Japanese Beetle will feed on over 300 species of plants eating the leaves, flowers, overripe or injured fruit. They feed en masse, starting at the top of a plant and working their way down. They prefer plants in full sun and are most active on warm sunny days. Food of choice would be roses and linden trees. As bad as it would be for the homeowner if the Japanese Beetle got established here, it would be doubly bad for the nursery industry. All plants from Idaho would be quarantined. That means any plants shipped out of state would have to be inspected and certified Japanese Beetle free, an added expense for the nursery. If you suspect an insect in your garden of being a Japanese Beetle, please call Jodie Ellis at the Idaho Department of Agriculture (332-8620) and get the instructions for having her take a look at your insect. Let’s be vigilant and stop this insect in its tracks.

Thank you to Jodie Ellis and the Idaho Department of Agriculture for all the images. Please see credits below.

Clemson University – USDA Cooperative Extension Slide Series,

John A. Weidhass, Virginia Polytechnic Institute and State University,

David Cappaert, Michigan State University,

William Fountain, University of Kentucky,

Beetle-trap Colorado State University

Japanese beetle trap Farm and Fleet

JB Life Cycle University of Kentucky

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes:

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>