“The Forest Tent Caterpillar is a native insect which is found in forests across North America. About once every decade, their population explodes causing heavy, but usually localized, defoliation, ” said David Carmichael, horticultural technician with the Department of Agriculture, Fisheries, Aquaculture and Forestry. “As a rule, the effects are minimal and short term, and most trees and shrubs recover easily. However, unhealthy or stressed trees, or trees which had been defoliated three or more times in the last few years may experience more damage or mortality.”

The insect’s natural cycle means that populations have been building over the last few seasons setting the stage for this year’s outbreak. Last winter’s conditions were favourable for egg survival and the long, cool Island spring provided plenty of food for the newly emerged larvae.

At this time of year, the caterpillars migrate in search of food. They prefer hardwoods such as poplar, sugar maple, white birch, and willow but will eat other species when food supplies become short. When high populations result in complete tree defoliation, the caterpillars often move around a great deal in search of food and their movements have caused them to be called "armyworms" by some.

Carmichael said that most control methods are impractical once the outbreak occurs. “The sheer numbers of insects means that killing hundreds or thousands can have little or no effect because there are so many more moving in to take their place,” he said.

For people who want to try and deal with the outbreak, he offered the following advice. Water can be used to spray the caterpillars off trees and shrubs. Special insecticidal soaps can be used to kill them but in order to be efficient, the soap must be sprayed on the caterpillars, not just on leaves. Insecticides such as Malathion or Methoxychlor can be effective, but they need to be used with caution. The label contains vital information on toxicities and any potential damage to other garden plants and beneficial insects.

Sticky bands can be wrapped around the trunk to stop insects from traveling up and down the tree. These bands can be purchased from garden centers or made at home by using duct tape and a waterproof sticky material such as petroleum jelly. Bt., a bacterial insecticide, can be applied next spring when the leaves emerge to kill off the larvae which feed on those bacteria coated leaves.

“The good news is that these insects are nearing the end of the feeding stage, so the outbreak should end in the next week,” said Carmichael. For more information, please contact: David Carmicheal, 368-4700.