Pest: Viburnum Leaf Beetle (Pyrrhalta virburni)
The Viburnum Leaf Beetle was officially identified in Massachusetts in the summer of 2004. Active populations were present in New York State, Maine, and Quebec Canada for many years prior to that. Both the immature and adult stages are serious defoliators of many viburnums. It is expected that this pest will continue to spread in Massachusetts and other New England states.
This native of Europe feeds exclusively on many different species of viburnum, which include: Viburnum opulus (and cultivars), V. dentatum, and V. rafinesquianum. Adults have also been found feeding and laying eggs on V. lentago, V. acerifolium, and V. trilobu.
This pest over-winters as an egg on the twigs of the host plant. Eggs hatch in May of the following year and the young larvae begin feeding on the host plant foliage. Larvae are usually found feeding together in groups. Pupation occurs 8-10 weeks later and the first adults begin to appear around the middle of July. Adults are active up until the first frost. Mating occurs, starting in July, and the female will chew small holes in the twigs where she lays her eggs. She then proceeds to cover these individual eggs with excrement giving the bark of these twigs a roughened appearance. Each female produces up to 500 eggs. (Source: Insects That Feed on Trees and Shrubs. Johnson and Lyons).
Injury and Appearance:
Both the larvae (immatures) and the adults feed voraciously on the foliage of the host plants. Heavily attacked plants will have every leaf skeletonized by this pest. It is the only pest that causes such injury to viburnums.
Adults are small and brown and somewhat difficult to see. The immatures are dark in color and can be found feeding in groups on the host foliage.
Managers need to be aware of the signs of this beetle's injury along with knowing what the different life stages look like. One should also monitor for the eggs on the stems of viburnums. When found, this pest should be treated to limit its injury and spread. Physical removal of this pest from the host plant is difficult to obtain especially when many plants are involved. Therefore, pesticide treatments may be necessary to manage this pest, once found.