Pyrrhalta viburni adults’ feeding damage consists of irregular circular holes, and severe feeding can nearly defoliate shrub. When disturbed, the beetles will fly away or drop to the ground. Skeletonized leaves in the spring (May-June) and heavily chewed leaves in the summer (July-September) indicate a viburnum leaf beetle infestation. The span from egg hatch to adult can be as quick as two months. Despite this, only one generation per year has been reported. They are mainly moved on infested live viburnums. Hosts include Viburnum species, especially arrowwood viburnum, European cranberrybush viburnum and mapleleaf viburnum.
Spread
Pyrrhalta viburni is a native of Europe. It is known to be established in New York, Maine, New Hampshire, Vermont, Washington State, and a small part of Pennsylvania and Ohio.
Ecological Threat
Heavy infestations of Pyrrhalta viburni cause defoliation, and plants continuously defoliated for two to three consecutive years may be killed. European cranberrybush can be very susceptible to damage by larval and adult feeding. In addition to heavy foliar damage, the inflorescences may be fed upon by larvae.
Adults
Adults are 1\/4 to 1\/3 of an inch long. The head, thorax, and elytra (wing covers) are generally brownish and the shoulders of the elytra are darker. The dorsal (back) surface has small, dense punctures, and the space between punctures is covered with thick, golden-grey pubescence. Females deposit up to five eggs in holes dug in new growth. The hole is capped with cement made from plant fiber, spit and a little excrement. These are visible throughout the summer, fall, and winter months.
Larvae
Egg hatch usually occurs in early May. These young larvae are greenish-yellow and skeletonize viburnum foliage, usually starting with lower leaves and leaving only midribs and major veins intact. As the larvae mature, they grow to about 1\/3 of an inch long, darken and develop a series of dark spots. Mature larvae migrate to the soil to pupate. Adults emerge from the soil and return to feeding on foliage.
Control
The best management option for Pyrrhalta viburni is to prune and destroy the twigs infested with egg masses and while beetles are inactive, usually from October to April. Soil application of systemic insecticides can be effective but their use may be restricted so contact your local Cooperative Extension Service Agent for more information on their use.