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Ministry of Agriculture, Food and Rural Affairs

Gypsy moth

Mature gypsy moth larva Gypsy moth “shothole” feeding injury on leaves Gypsy moth
Click to enlarge.

Beginner

Scientific Name
Lymantria dispar (Linnaeus)

Identification
Eggs:

  • In masses containing from 300-1,000 eggs,
  • Covered with a fibrous mat of hairs,
  • Buff coloured initially, and later bleach with exposure.

Larvae:

  • Yellow, gray or black with long wispy hairs,
  • Starting just after the head, there are five pairs of blue spots followed by six pairs of red spots down the back,
  • Immature larvae are about 6-7 cm in length,
  • Full grown larvae are 30-65 mm in length and very hairy,
  • When not feeding, they rest on a mat of silk they make on the underside of the leaf.

Pupae:

  • Covered with brown, tear-drop shaped protective shells,
  • About 2.5–5 cm long.

Adults:

  • Black and white,
  • Female has white wings with black patterns,
  • Males have dark gray wings with lighter coloured patterns.

Damage:

  • Shothole feeding on the leaf.

Often Confused With
Starting just after the head, there are five pairs of blue spots followed by six pairs of red spots down the back. These spots distinguish gypsy moth larvae from any other large, hairy larvae like the white marked tussock moth.

Period of Activity
Gypsy moth overwinters as egg masses. The egg masses hatch in the spring and larvae emerge and begin feeding on leaves from tight cluster through bloom. Larvae pass through five to six larval instars, and then enter the pupal stage in mid summer. The larval stage lasts approximately 40 days from egg hatch to pupation, and the pupal stage lasts about two weeks. Overwintering eggs are laid in August and December. There is only one generation per year.

Scouting Notes
Take note of gypsy moth activity during regular orchard inspections while monitoring for other pests. During the period between tight cluster to petal fall, check 5 terminal shoots and 5 fruit buds in each of 10 trees (50 terminals and 50 fruit buds in total) for signs of caterpillar feeding activity. After petal fall monitor 10 terminals on 10 trees for the presence of feeding damage. Gypsy moth are usually only present in orchards until July.

Thresholds
An insecticide is generally recommended when the action threshold of 12-15 larvae per 100 terminals and fruit buds is observed.

Advanced

Scientific Name
Lymantria dispar (Linnaeus)

Identification
Egg masses contain from 300-1,000 eggs and are covered with a fibrous mat of hairs. They are buff coloured initially, and later bleach with exposure. Larvae are yellow, gray or black with long wispy hairs. Starting just after the head, there are five pairs of blue spots followed by six pairs of red spots down the back. These spots distinguish gypsy moth larvae from any other large, hairy larvae. Immature larvae are about 6-7 cm in length. Gypsy moth pupae are covered with brown, tear-drop shaped protective shells about 2.5–5 cm long. Adult moths are black and white. The female has white wings with black patterns, and males have dark gray wings with lighter coloured patterns. Full-grown larvae are 30-65 mm in length and very hairy. Adult females cannot fly and rely on pheromones to attract males for mating.

Larvae chew on the leaves, leaving small holes referred to as shothole feeding on the leaf. When not feeding, they rest on a mat of silk they make on the underside of the leaf.

Often Confused With
Starting just after the head, there are five pairs of blue spots followed by six pairs of red spots down the back. These spots distinguish gypsy moth larvae from any other large, hairy larvae like the white marked tussock moth.

Biology
Gypsy moth overwinters as egg masses of 100-1,500 eggs on tree trunks and the undersides of branches and bark. The egg masses hatch in the spring and larvae emerge and begin feeding on leaves. Larvae pass through five to six larval instars, then enter the pupal stage in mid summer. First to third instar larvae feed from dawn to mid morning, then seek shelter from the heat of the day under bark or in ground cover. Fourth to sixth instars feed at night from sunset to sunrise, but if population density is high larvae will feed day and night. The larval stage lasts approximately 40 days from egg hatch to pupation, and the pupal stage lasts about two weeks. Overwintering eggs are laid in August and December. There is only one generation per year.

Period of Activity
Larvae emerge and begin feeding on leaves in the spring from tight cluster through bloom. In mid summer they enter the pupal stage which lasts about two weeks. Gypsy moth are usually only present in orchards until July.

Scouting Notes
Take note of gypsy moth activity during regular orchard inspections while monitoring for other pests. During the period between tight cluster to petal fall, check 5 terminal shoots and 5 fruit buds in each of 10 trees (50 terminals and 50 fruit buds in total) for signs of caterpillar feeding activity. After petal fall monitor 10 terminals on 10 trees for the presence of feeding damage. Gypsy moth are usually only present in orchards until July.

Thresholds
An insecticide is generally recommended when the action threshold of 12-15 larvae per 100 terminals and fruit buds is observed.

Management Notes:

  • Many predatory and parasitic insects attack spring-feeding caterpillars. Predators include ground beetles (Carabidae), stink bugs (Pentatomiidae), assassin bugs (Reduviidae) and spiders. However, beneficial insects are not usually effective in providing economic control.
  • To conserve and encourage natural enemies of spring-feeding caterpillars, apply insecticides only if the action threshold is reached and then select the most benign and narrow-spectrum materials available. For more information on the toxicity of pesticides to beneficial insects click here.
  • Birds such as chickadees, bluebirds, warblers and woodpeckers also feed on caterpillars, however they do not provide adequate control.
  • Parasitic wasps (Braconidae, Ichneumonidae) and flies (Tachinidae) attack caterpillars and minute Trichogramma wasps often parasitize moth eggs.
  • A number of fungal and viral diseases also impact caterpillar populations, particularly during warm, wet springs.
  • Insecticide options are provided in OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :