Help us watch the Japanese beetle
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Issue: September 1st, 1997


Help us watch the Japanese beetle

Question:

We may have a new pest in New Mexico. The Japanese beetle has been a problem in eastern and north central states for a long time, but its presence was confirmed for the first time in New Mexico this summer. Will you and the readers of "Yard and Garden" assist the New Mexico Department of Agriculture in surveying for additional occurrences of the Japanese Beetle in New Mexico?

Carol Sutherland, New Mexico Department of Agriculture

Answer:

Dear readers: This is an alert as well as a call for assistance. According to Dr. Sutherland, NMDA entomologist, we have been fortunate that the Japanese beetle has taken so long to show up in New Mexico. In states where the pest is established, production of nursery srf are highly regulated by state and federal agencies in an effort to curb its spread. We are asking for your help in monitoring in New Mexico to prevent it from gaining a foothold here.

If you find beetles in your garden which fit the description of the Japanese beetles presented below, please collect a sample, kill it in a leak proof container of rubbing alcohol, and take the specimen to your local Cooperative Extension Office along with a label including your name and the street address where the specimen was collected. This information will be sent to the New Mexico Department of Agriculture to verify that it is a Japanese beetle and to allow them to track this new pest in New Mexico. Your assistance will be greatly appreciated. According to Dr. Sutherland, the Japanese beetles do not bite or sting, but the short spines on their legs may feel prickly. You may prefer to use a cup or jar to capture the beetle.

The Japanese beetle has been a major pest of landscapes and fruit trees in the U.S. since it was first introduced around 1916. It has severely damaged lawns, golf courses, pastures, shrubbery, flowers, and fruits. It is described as one of the most destructive of garden pests and has over 300 species of plant hosts. The beetles are gregarious and can be found in groups of 20 to 30 beetles which quickly defoliate a plant and decimate a landscape. The juvenile forms of this beetle are grubs which live underground feeding on the roots of grasses as well as many other plants, weakening and killing them.

The adult beetles may be recognized as colorful insects with a metallic blue or green pronotum, the area between the head and the wings; one color variant has a metallic copper head and pronotum. The wings are coppery in color. They have two conspicuous white spots and several smaller spots near the end of the abdomen. They are quite active during daylight hours. According to Dr. Sutherland, they are good flyers, but lousy landers. Their ability to fly should increase our apprehension regarding the spread of this pest through our landscapes. To distinguish between Japanese beetles and May and June beetles, the Japanese beetles are about one-half inch long while the May and June beetles five-eighths inch or more in length. The May and June beetle also lack the white spots on the abdomen.

The grubs resemble the familiar white grubs (larvae of the June beetles) which New Mexico gardeners have known for some time. However, the Japanese beetle is a greater threat to our gardens than the May and June beetles. During the warm season the grubs reside near the surface in the soil, feeding on plant roots. When the soil is cool in the winter, the grubs burrow six to twelve inches deep and construct earthen cells in which they pass the winter. In the spring they return to the surface, feed for a few weeks, then form their pupal stage which lasts for about six weeks. The adult beetles then emerge to feed on our gardens and landscape plants. Dr. Sutherland states that there is usually one generation annually with adults emerging from their pupae from mid-May through mid-August.

If it becomes necessary, control may be accomplished by application of appropriate insecticides. At this point in time we need to determine if there are more Japanese beetles in New Mexico and where they are located. The beetle confirmed thus far may have hitchhiked on nursery products originating in an infested area. If so, we may have no need for control efforts. Or, it could indicate a bigger problem. In that case, insecticides labeled for control of beetles may be needed. Spores of milky spore disease are sold under several trade names. Although they are ineffective against our common May and June beetles, they may be used successfully to control Japanese beetle larvae. Hand picking adults, knocking them into jars of kerosene and water can also be helpful. If infestations are severe and you cannot wait for the milky spore disease to work, or your timing is wrong, there are other insecticides labeled for control of beetles and grubs. Be sure you choose an appropriate product for control of Japanese beetles on the plants they are affecting and then follow the directions on the label.