The Gypsy Moth

by: Dr. T.D. Smith
SPRING 1987

The gypsy moth Lymantria dispar (Linn.) was introduced to Massachusetts from Europe in 1869 to part of a silk-making experiment. Some of the larvae escaped and the gypsy moth has been an increasing problem in Canada and the United States ever since. It arrived in Nova Scotia in 1980 and has settled in.

The forests of Nova Scotia have enough of the tree species gypsy moths like to support a major infestation. Larvae feed voraciously on the leaves of a wide variety of both hardwood and softwood trees but oak, poplars, birch, alders, beech, apple and sugar maple are preferred. It is known to successfully complete its life cycle on 500 species of plants in the world.

The insect passes the winter in the egg stage, frequently on the bark of trees, but also in protected places (e.g. in rock piles, beneath logs, and on the under surfaces of recreational vehicles or equipment, which are instrumental in the spread of the insect). The eggs hatch in spring and the larvae ascend the trees to feed on young leaves. Initially the larvae feed during the day, but as they grow older, they feed mainly at night. Then they tend to congregate in sheltered niches of trees, and larger larvae may even move down to the ground litter.

Feeding is complete in July. The full-grown larvae, 35 to 60 mm long, are dusky or sooty coloured and hairy, and have a double row of five pairs of blue spots, followed by a double row of six pairs of red spots down the back. They seek sheltered places in which to pupate. Pupae may be found attached by silken thread to branches or trunks of trees, rocks, forest debris, buildings or fences. the moths emerge in 10 to 14 days. the light brown male moth is slender and has a wingspread of about 37mm. It is quite unlike the larger, light coloured, heavy-bodied female. Mating and egg laying occur near the pupation site. The eggs are laid in masses of 100 to 1000 and are covered with a mat of buff-coloured hairs from the female's body.

Since female moths do not fly, natural spread can occur only in the caterpillar stage. Young larvae are particularly light and buoyant because of their long hairs. When disturbed, they spin down on a silken thread and are readily blown about by the wind, sometimes for considerable distances. Man also involuntarily helps the spread of this pest by transporting logs, trees, firewood, lumber or stones on which eggs have been laid. Recreational and other vehicles travelling in or from infested areas also carry eggs, larvae or pupae.

There are several things that a homeowner can do to reduce gypsy moth around their property.

REMOVE NESTING SITES

Gypsy moth caterpillars like to rest in dark, dry spots during the day, especially as they grow larger. Also, when the caterpillar stage is completed they will use these sheltered areas to pupate, after which the female moths will emerge and lay eggs close by. Unfortunately, the natural enemies of the gypsy moth, which include mice and other small mammals, birds, various reptiles and amphibians, wasp and fly parasites, ants, beetles and spiders, work more efficiently when they don't have to search for their prey. Therefore, the fewer hiding places there are, the more gypsy moths will be removed by these parasites and predators and the fewer you will have on your trees and shrubs.

The gypsy moth utilizes any natural resting sites including the undersides of living and dead limbs, loose and deeply fissured bark, rocks and fallen trees. For the most part, it is impossible to eliminate a significant number of these natural site. However, the gypsy moth also utilizes any available artificial resting site, and it is here that the homeowner can make an impact.

Anything that a caterpillar can crawl under that is placed on or near a favoured gypsy moth food plant can become a resting site. Some common backyard gypsy moth "hot spots" are tree houses, trespass signs, stacked fuelwood and lumber, junk piles, old tires, rock piles, picnic tables, and outbuildings. Eliminating these preferred hiding spots can help slow gypsy moth buildups. Even beneficial items such as bird boxes and feeders, which should be provided to encourage the presence of birds, are excellent resting sites. Examine and remove any resting caterpillars from them frequently.

DESTROY FEMALE MOTHS AND EGG MASSES

Each female moth or egg mass you destroy eliminates an average of 500 caterpillars from next year's gypsy moth population. Female moths are flightless and crawl from their pupation sites to mate and lay eggs. Look for the white females and buff-coloured, nickel-to-quarter size egg masses beginning in mid-August in Nova Scotia. Carry a spoon and a jar or tin can half full of strong detergent solution with you as you search the tree trunks, loose bark flaps, and other dry, sheltered sites. Scrape any moths and egg masses you find into the solution and let it stand a day or two before discarding. You may remove and destroy egg masses any time between September and the following May, since the eggs usually don't begin hatching until mid-May in southern Nova Scotia. Do not merely scrape them onto the ground. This will not kill the eggs, and winter snows will actually blanket and protect them from natural enemies.

Vegetable cooking oil will effectively kill the eggs if properly applied. The egg masses need only to be wetted with the vegetable cooking oil to the point of dripping. Oil can either be applied with a basting brush or a window washing fluid sprayer. The vegetable oil will not harm thin-barked trees. However, do not use petroleum-based substances like grease, oil, tar or creosote as these and many other household products can soak through thin tree bark and kill the living tissue beneath.

The hairs covering gypsy moth egg masses, as well as caterpillar hairs, can cause temporary rashes on some people. Wear gloves to prevent this.

Most homeowners don't realize that they have a gypsy moth infestation until they begin to see caterpillars or the damage they cause. There are several proven ways to reduce the number of caterpillars and protect your landscape plants.

TRAP CATERPILLARS

Technical gypsy moth controls do not involve the use of insecticides to kill caterpillars. The most widely used mechanical device is the burlap skirt. Burlap skirts are actually traps designed to provide sheltered resting sites for caterpillars. because you install them at chest level, the resting caterpillars are easy to collect and destroy with your spoon and detergent. Avoid slicing or stabbing the caterpillars with a sharp instrument, since you may puncture and damage tender tree bark! The burlap skirt is simply a 30 -45 cm wide band of burlap cut a little longer than the distance around the tree. Wrap the band around the tree, overlapping the ends, and tie securely around the middle with baler twine. Fold the top half of the band down over the bottom half to form a loose skirt. Make sure that the skirt flares out and that the bottom edge hangs loosely. Band all trees and check every day or two by lifting the skirt to collect hiding caterpillars.

Gypsy moth life forms (eggs, larvae and pupae) have been found in Nova Scotia. If you find or suspect that you have gypsy moth on your property, telephone the nearest Department of Lands and Forestry and ask for or leave a message for the Pest Detection Officer. The PDO will return your call as soon as possible. Remember that one destroyed egg mass means 500 fewer larvae to feed on your tree next spring.