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What’s Eating My Roses? – Hoplia Beetles

Excerpted from University of California Pest Notes

This is the time of year when many people find small, squarish, iridescent beetles happily eating their roses and other white or light-colored blossoms. Don´t worry, they´re not Japanese beetles (there are currently no known populations of Japanese beetle in California). They are, however, close relatives of the dreaded Japanese and Chinese Beetles, known as Hoplia beetles.

The hoplia beetle, Hoplia callipyge (family Scarabaeidae), is a common pest of roses and other plants in many parts of California. Because it has just one generation a year, it is a problem only from late March to May, depending on the weather and area of California. If you can be patient and tolerate the damage, the hoplia beetle-and its associated chewing damage-will go away.

{b” >Identification{/b” >

The adult beetle is oval shaped, about 1/4-inch long. Most of the body is a beautiful iridescent silvery-green in sunlight. The larvae are small, crescent-shaped grubs that live in the soil.

{b” >Life Cycle{/b” >

Female beetles lay glossy white eggs in areas of undisturbed vegetation, such as in fields, along fences and ditches. The larvae feed on decaying vegetation and plant roots but do not damage woody plant roots. They develop slowly, remaining in the larval or pupal stage throughout the winter. In early spring they complete development and adult beetles emerge from the soil. The adults fly to gardens where they feed on roses and other flowers. Adults are generally active from late March to early May. After feeding for several weeks, adults fly back to their egg-laying sites. There is a single generation each year.

{b” >Damage{/b” >

Hoplia beetle adults are especially attracted to light-colored flowers and chew round holes in the petals of white, yellow, apricot, and pink roses. Early buds and flowers of roses may be destroyed by chewing. The beetles do not feed on leaves. Hoplia beetles also feed on the flowers of calla, citrus, irises, lilies, magnolia, olive, peonies, poppies, and strawberries, and on the young leaves and fruit of grapes, peaches, and almonds.

{b” >Management{/b” >

One way to manage hoplia beetles in your garden is to regularly hand-pick them off the flowers they are feeding on and dispose of them in a bucket of soapy water, or shake them out of the blooms directly into the soapy water. You can also just clip off blooms infested with beetles and dispose of them. Regular hand-picking may be an important way of reducing future beetle populations in the immediate area.

Another nonchemical control measure is to fill white, 5-gallon buckets with water and a few drops of detergent to break the surface tension. These buckets are then placed in several locations throughout the rose garden where they attract the beetles, which fall in the buckets and drown. The effectiveness of this method has not been tested by research. Like hand-picking, it may only serve to reduce the beetle population somewhat.

When planting roses in an area where these beetles are plentiful, consider choosing darker-colored varieties such as red roses to help avoid problems with this pest.

Sprays are not generally recommended. It is very difficult to obtain effective control with insecticides because beetles are protected within the blossoms and they must be contacted directly by the spray to be killed. Spray insecticides only kill those beetles present at the time of the spray applications. Do not spray blooming plants where honeybees are present, because most insecticides are very toxic to honeybees.

Chemical control of the larvae in most cases is not possible because they may live in the soil outside the garden or in surrounding landscapes. Systemic insecticides aren´t effective against the adults because concentrations high enough to be toxic do not occur in the blossoms where they feed.

Avoid use of these insecticides when possible. They are harmful to natural enemies and some materials have been found in urban surface water systems at levels that warrant concern.

If chewing damage cannot be tolerated for the two to four-week period that the beetles are present, please contact the Master Gardener office at 209.533.5696 for pesticide recommendations. You can also visit www.ipm.ucdavis.edu to read the complete set of pesticide recommendations and warnings provided by the University of California Integrated Pest Management (IPM) program.