CO-Horts Blog

Thursday, July 23, 2015

Beauty is Only Skin Deep

Posted by Deana Wise, Broomfield County Extension

Beauty Is Only Skin Deep

        In our world, beautiful people are envied. They are viewed as being more successful, happier, and lead more interesting lives. In the insect world, some of the most beautiful are the most threatening to our urban landscapes. We seek to destroy them at all cost.
Fig. 1 Japanese beetle adult.
Photograph courtesy of David Cappaert/University of
Michigan and
          One example is the dreaded Japanese beetle (Popillia japonica). This metallic green pest with brown wing covers, white spots and distinctive antennae (Fig. 1) has been a major problem in the eastern U.S. for close to a century. The adults munch on a wide variety of plants (between 200-300) while the larval form feeds on the roots of grasses. This indiscriminate grazer can rid your garden of flowers, buds and leaves from Roses, Virginia Creeper, and American Linden among others. It has settled in Colorado.
Fig.2 Grub
Photo retrieved from
       The grubs are white with dark heads and the thorax has 3 pairs of well-developed legs (Fig.2). They are usually curved in a C shape and have a distinctive V-shaped rastral pattern (Hairs on the hind end). They feed on the roots of grasses, reducing the plant’s ability to absorb water. Heavily infested turf can be easily pulled up, revealing the grubs beneath.

          The adult emerges from the soil in June and feeds for 4-6 weeks. After mating, the female lays 40-60 eggs, 2-3” deep into the soil. The larva remains in the soil for up to 10 months (Fig. 3).   They prefer well maintained, damp turf. The eggs and newly hatched grubs can be damaged or killed by excessive drying of the soil. Older grubs simply move down deeper to survive. They are not affected by overly damp soils.

Fig.3  Japanese beetle lifecycle
Photo retrieved from

          Control of Japanese beetle can be achieved in various ways. One satisfying alternative is to pick the beetles off and deposit them into a container of soapy water or mineral spirits. If you don’t care for hand to hand combat, there are several insecticides labeled for both Japanese beetle stages.

The adults can be killed with various pyrethroid, permethrin, and Carbaryl products.  Neem products or Pyola (pyrethrins in canola oil) are botanical alternatives. As with all chemicals, follow the label and use caution when applying to plants where bees are present.

The grubs can be treated by several methods. Certain parasitic nematodes in the genus Heterorhabditis can be applied to the soil when grubs are present. Another popular biological control is Bacillus popilliae or milky spore. Insecticides include: imidacloprid, chlothianidin, and chlorantraniprole. As with any chemical, it is very important to follow the label.

For more information see fact sheet no. 5.601, Japanese Beetle.


  1. It is also quite satisfying to squish the bugs between one's (gloved) thumb and index finder.

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