The white-marked tussock moth, scientifically known as Orgyia leucostigma, is a moth belonging to the family Erebidae. The genus name Orgyia originates from the ancient Greek word ὄργυια, meaning 'outstretched arms'. This moth is native to North America and can be found from Alberta to the maritime provinces. The white-marked tussock moth is known for its periodic outbreaks in large numbers. While primarily a pest of broad-leaved trees, it also attacks coniferous species when its population is high.
Appearance and Identification
The larvae of the white-marked tussock moth are brightly colored and possess distinctive tufts of hair-like setae. Key features include:
- A bright red head.
- Yellow or white stripes along the body.
- A black stripe along the middle of the back.
- Bright red defensive glands on the hind end of the back.
- Two long black tufts of hair on each side of the head and one near the hind end.
- Four greyish brush-like tufts and two bright red spots on its back
- Four dense white clumps of short setae on the top of the first four abdominal segments
Mature caterpillars can grow to about 38 mm long. The caterpillars spin a grayish cocoon in bark crevices and incorporate setae in it. The males are gray with wavy black lines and a white spot on the forewings. The antennae are very feathery. The females have reduced wings and do not leave the vicinity of the cocoon.
Feeding Habits and Host Plants
Tussock moth caterpillars are herbivorous, feeding on the leaves of various trees and plants. They are generally diurnal, actively feeding throughout the day and resting at night. The caterpillars have a wide range of host plants, including both deciduous and coniferous trees, shrubs, and other plants.
The white-marked tussock moth caterpillar is known to feed on a diverse diet of woody plants. Some of their preferred host plants include:
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- Oak
- Cherry
- Hackberry
- Willow
- Balsam fir
- Tamarack
- American Elm
- Yellow Birch
- Witch-hazel
- Various oaks and hickories
- Eastern Hemlock
- Apple
When trees are severely defoliated, the caterpillars may migrate to gardens or fruit trees and feed on almost every green crop, sometimes invading summer residences in the process of migrating. The caterpillars' food preferences may vary from time to time and in different places.
Impact as a Pest
The white-marked tussock moth can be a significant pest, particularly during outbreaks when their numbers are high. They primarily infest broad-leaved trees but also attack coniferous species such as fir, spruce, and larch. Severe infestations can cause significant defoliation, leading to damage to Christmas trees and other economically important plants. Moderate to severe infestations of this defoliator have occurred in the past over extensive areas exceeding 500,000 hectares. In New Brunswick it has been found mainly in Westmorland and Albert counties, while in Nova Scotia the infested counties have been Cumberland, Colchester, Lunenburg, Hants, and Halifax. In both provinces, defoliation is most evident on balsam fir, tamarack, and hardwoods, but field crops can also be affected.
Life Cycle
The eggs hatch in late June or early July. The caterpillars feed for about 6 weeks growing to about 38 mm long. After feeding for several weeks, the caterpillars eventually grow 1 to 11/2 inches long. They spin loose grey cocoons within which they transform to pupae. Greyish moths emerge about 2 weeks later. The males are winged and the females are wingless. The female lays its eggs on or near the cocoon. The insect overwinters as eggs in a mass laid in or on the mother's cocoon. In spring, the eggs hatch and the tiny, hairy caterpillars begin to feed and grow.
Control Measures
When the caterpillars are young and actively feeding, Bacillus thuringiensis formulations can give adequate control. Young caterpillars are also susceptible to pyrethroid insecticides available at most garden centers.
Natural Enemies
Whitemarked tussock moth caterpillars are plagued with diseases, parasites, and predators, which may explain why they are seldom wide spread pests. Tussock moth caterpillars face a variety of predators, including birds, mammals, and insects. Birds such as chickadees, nuthatches, and woodpeckers are known to feed on tussock moth caterpillars. Many species of mammals, including squirrels, chipmunks, and deer, also feed on tussock moth caterpillars. Additionally, insects, such as lady beetles, lacewings, and wasps, prey on tussock moth caterpillars. Parasitic Braconid wasps, like the Cotesia melanoscela and Apanteles melanoscelus, lay their eggs on the tussock moth caterpillars, and when the wasp larvae hatch, they feed on the inside of the caterpillars, eventually killing them. The fungus Entomophaga maimaiga was introduced to North America to control the spongy moth (Lymantria dispar). The fungus also infects O. leucostigma and could possibly have an impact in years when E. maimaiga is abundant.
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Potential Allergic Reactions
Some of these setae contain urticating material that can cause dermatitis on sensitive skin. CAUTION: Avoid handling the caterpillar, as its hair is known to cause allergic reactions, especially in areas of the body with sensitive skin (e.g. back, stomach, inner arms).
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