Gypsy Moths

Gypsy moths have been a major problem in the Golden Horseshoe for the past few years. Infestations have been so high that some municipalities have initiated an aerial spray program to try and control the problem. These moths are present in many areas of Ontario including Halton.

As with many of our pest species, this is another non-native insect. It is believed to have been first introduced in Massachusetts in the 1860’s and has become widespread in the Northeastern US and Eastern Canada. It is responsible for feeding on or defoliating millions of acres of trees each year.

Gypsy moths probably were named from their ability to travel and spread by attaching to a wide variety of objects including wood products, vehicles, campers etc. Small caterpillars can also be picked up and carried by the wind. These moths over winter in egg masses attached to the bark of trees. Egg masses, which vary in size from a dime to a toonie are buff coloured, covered with hairs from the female and can contain 100 to 1,000 or more eggs. Trees can have egg mass counts in excess of 800 per tree. This could potentially result in 400,000 to 600,000 caterpillars on an individual tree. The eggs hatch into small caterpillars in the spring and feed till early July growing to about 6cm (2.5 inches) in length. Caterpillars, which are hairy, can be identified by the 2 rows of coloured dots on their backs with five pairs of blue dots and 6 pairs of red dots. Use this dot pattern to distinguish gypsy moth caterpillars from tent caterpillars for which they are sometimes mistaken. The adult moths are present in late July and August. Female moths are whitish with black markings and cannot fly. Males are brownish and are able to fly, being attracted to pheromones released by the females.

Gypsy moth larvae will feed on a wide variety of trees but broad-leafed deciduous trees are preferred. Trees commonly attacked include oak, poplar, birch, apple and cherry. They will also feed on evergreens and shrubs. Heavy infestations can result in severe defoliation of trees. Healthy trees can withstand a single defoliation but weakened trees or defoliation several years in a row can result in the death of the tree. Severe outbreaks in residential areas result in large numbers of caterpillars crawling over sidewalks, decks, the sides of buildings etc. Some people develop allergies to the hairs of the caterpillars.

Control of gypsy moths can be carried out in several ways. If you have red oaks on your property, monitor these trees as they are one of the preferred hosts of the moths. Early in the spring, egg masses can be removed from the bark of trees and destroyed or sprayed with dormant oil. Traps can be placed around the trunk of trees which will catch the larvae as they try to crawl up the trunks. These traps can be made from burlap sacs or with a sticky band encircling the trunk. Pheromone traps are available to attract and kill the male moths. Municipalities in their aerial spraying programs use a biological insecticide known as Btk which affects the caterpillars. Spot treatment of infestations on individual trees can be done with insecticides containing carbaryl or permethrin.