Viburnum leaf beetle larvae can do a great deal of damage early in the season. The larvae begin to feed even before the leaves are fully expanded. They will skeletonize the leaves, eating the tissue between the veins. Infested shrubs may try to produce a new set of leaves during the time when the larvae are pupating and becoming adults. The production of a second set of leaves puts stress on the shrub. The adult beetles, which emerge in mid-summer, also feed on the leaves, producing additional damage and stress. They can feed from mid-summer until frost. Since both the larvae and the adults can feed, damage occurs over the majority of the growing season and it can be quite extensive on highly susceptible species. Heavy feeding for two to three years can lead to the death of a viburnum.

Viburnum leaf beetle has one generation per year. This insect overwinters as eggs in the tips of twigs of the host plant. The female beetles will lay their eggs in cavities they chew into the stems. Three to eight eggs are laid in each cavity, then the cavity is capped with the chewed wood. Egg-laying will occur from late summer into autumn, with each female able to lay as many as 500 eggs.

New larvae will start to hatch out around mid-May in most years, and will move to the new leaves to feed. The larvae are tiny upon hatching and will only reach about 1/3 of an inch in length at maturity. Feeding damage (holes) may be noted before the actual insect is seen. The larvae vary in color from pale green to pale yellow. The body is marked with black dots along the sides and a row of black dashes along the back. As the larvae grow, they will molt and shed their skin, so cast off skins may be noted on the leaves of the host plant. The larvae will go through three instars, growing as they molt.

From early to mid-June, the larvae will crawl down the stems to pupate in the soil. Pupation takes about ten days. After that time, the adult beetles will emerge and they will also feed on the leaves, continuing to skeletonize them. Adult beetles are fairly nondescript and are easily overlooked. They are brown and about ¼ inch in length, with the females being slightly larger than the males. Close inspection reveals that the insect is covered with fine golden hairs. Adults will generally be present from early July until frost.

Egg-laying sites may be seen on twigs from fall until spring. The actual eggs are not visible. The eggs are laid in small holes on the twigs and then the holes are capped with chewed wood. The caps are dark and stand out against the bark of the twig, making them easy to see. They are in rows on the lower side of the end of the twigs.

There are a number of ways to manage viburnum leaf beetle, but most methods need to be timed for a specific stage of the insect’s life cycle. Using more than one management technique may help give better results.

Cultural management: 

Consider planting the more resistant species of viburnums. Susceptible species do not have to be abandoned, but it may be wise to plant them in moderation. Excessive use of any species always has the potential to magnify pest problems.

One of the most effective ways to reduce the population of beetles is to remove and destroy the twig tips that bear the eggs. The egg-infested twig tips can easily be seen once the leaves have fallen. They can be removed from October through April. Once the twig tips have been removed, destroy them by burning (where permitted), chipping, or burying. Destroying the egg-laying sites greatly reduces the insect population and can also reduce the need to use insecticides.

A sticky barrier applied to stems may keep some larvae from crawling to the ground to pupate.

Biological management:

There are some insects that are predators on the viburnum beetle larvae. These include green lacewings, certain species of lady beetles, and soldier beetles. While these may reduce populations, it is not usually enough to be considered an effective management measure.

Chemical management:

If insecticides are used, it is best to treat young larvae as they are the easiest to kill. If larvae can be killed early in the season, the amount of feeding damage can be lessened. Insecticides can be applied to adults, but by that time there may be a lot of damage already done. The insecticides that are effective against the larvae are not always effective against the adults.

The pesticide information presented in this publication is current with federal and state regulations.The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum. Use pesticides safely and wisely; read and follow label directions.

For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).