Clever Bugs

Garden Clippings for June 9, 2018

Bugs are clever little buggers.  Case in point is the Viburnum Leaf Beetle.

The female adult Viburnum Leaf Beetle spends its summer in search of food and looking for a spot to lay its eggs.  She searches the landscape until she finds a Viburnum bush (snowball) and then begins to deposit nests of about 5 eggs.

The beetles know enough to understand that the best bet for survival for her young is a Viburnum bush.  Carefully she will make a hole at the end of a limb and will drop about 5 eggs per hole.  To protect the eggs, she will cover the hole with a mix of her own excrement and branch fibres.  She will drop about 100 groups of eggs.

At the end of summer, she will realize that her life of feeding and laying eggs has been good, and she’ll give up the ghost.  Her eggs will remain on the plant all winter long and will hatch precisely when the Viburnum sprouts its leaves in spring.  The larvae gorge on the tender leaves, eating voraciously, skeletonizing the foliage.  The green flesh is consumed, and the veins are left behind.  Feeding occurs for about 3 weeks.  In some cases, the entire bush is eaten up.

Once the larvae have had their fill, they will migrate down the limbs heading for soil.  In short order the larvae pupate and emerge as adults.  The adults, resembling a small beetle, immediately begin munching on whatever Viburnum foliage might be left behind.  Once again, the female will go on a hunt for a perfect spot to lay her eggs in summer.  The life cycle repeats itself.

Fortunately for the Viburnum, even if all the foliage is eaten up, the bush will likely produce a new set of leaves to replace the old ones that have been eaten up.  Most shrubs and trees have a second set of leaves in their back pocket that can be pulled up in case of an emergency.  Some horticulturalists will suggest that the act of pruning a bush with a pruning tool will have the same impact on the plant as an insect eating the foliage.

We do know that an insect’s decimation of a plants’ leaves for a few consecutive years will cause the host plant to die.  We also know that the life cycle of most insects is like that of the Viburnum Leaf Beetle.  The adult lays eggs in summer, eggs remain viable over the winter and emerge in spring as a small larva which soon morphs into an adult.

Controlling the Viburnum Leaf Beetle is not easy.  Chemical pesticides such as Carbaryl, Malathion and Sevin will provide good control, but these pesticides are not available for cosmetic use in Ontario.  Safer’s Soap, an organic pesticide will keep the larvae in check provided they are sprayed soon after the larvae emerge.  Diatomaceous earth, made from natural sources will also provide control, but since it is in dust form, might be awkward to apply.  The friendliest way to control Viburnum Leaf Beetle is to look for and prune off the small nests of eggs.  Be sure to take away or burn off the infected limbs.

Gardeners might not like the Viburnum Leaf Beetle for the damage it does to Viburnums, but we might give it top marks for cleverness.