A native of Europe, the viburnum leaf beetle, Pyrrhalta viburni (Paykull) is becoming a serious pest of viburnums in south central Ontario. It was first reported in North America in 1947, but was not found as an established population until 1978. The preferred host is the European highbush cranberry (Viburnum opulus L.) although it has been found on wayfaringtree (Viburnum lantana) and Rafinesque (Viburnum rafinesquianum) viburnums as well as other viburnums (table 1). Both the larvae and adult beetles skeletonize the leaves leaving only the midrib and larger veins. The beetles may cause serious injury to varieties of Viburnum opulus, and 2 to 3 consecutive years of severe defoliation may cause the death of the plant.

The adult beetles are approximately 5.5 mm long, and olive green in colour. They overwinter in the egg stage in holes in the twigs. In May the eggs hatch and the larvae may be found feeding in June. The insect pupates in the ground and adults emerge in July. The complete life cycle requires 8 to 10 weeks. In the late summer until the first frost, the females chew holes (1 x 1 mm) in a straight row (as many as 10 holes to a row) on the underside of twigs of the current years growth. Several eggs are deposited in each hole, and up to 500 eggs can be laid by each female. The holes are covered with a cap made of black excrement mixed with chewed wood and mucus which hardens when exposed to air. As many eggs may be laid on a particular shrub, severe defoliation can occur relatively quickly.