1. European Gypsy Moth (Lymantria dispar)

2. Why be Concerned about Gypsy Moth?
Tree defoliator
Attacks over 300 species of woody plants
Increases host susceptibility to secondary pests and pathogens
Native range and established areas: appears as an outbreak pest
Greatest damage occurs at first introduction
Over 1 million acres defoliated in the U.S. in 2010
Why is gypsy moth an important invasive species? It is a defoliator that strips trees of their leaves and it has a very broad diet, feeding on over 300 species of woody trees and shrubs. Complete defoliations can stress trees and leave them vulnerable to secondary pests and pathogens. As the first wave of gypsy moths come into Minnesota, trees that are not vigorous or are already under stress are more likely to die as they are impacted by gypsy moth.
In its native range in Europe and north Africa, gypsy moth is an outbreak pest that appears in pockets. The cyclical nature of the populations along with the impact of natural predators (NPV virus, Entomophaga fungus) keeps outbreaks localized. Defoliation topped 1.5 million acres in the US in 2008.

3. Local Impacts July ! Leaves are stripped
Trees are stressed, leaving them susceptible to other pests and diseases
Each caterpillar consumes 9 square feet of foliage!
Currently, gypsy moth defoliation averages of 880,000 acres annually (over the past 10 years).
July !
Photo courtesy of Garrett (MD) County extension Office

4. Landscape Impacts
The images depict heavy defoliation in Maryland in It is not uncommon to see complete defoliation during heavy outbreak years. Deciduous trees can and will re-leaf after a gypsy moth defoliation. Conifers do not have this ability which leads to greater tree mortality in that group.
Multiple years of gypsy moth defoliation can stress trees leaving them vulnerable to insects and disease. The presence of gypsy moth will eventually impact forest species composition. Gypsy moth has been in the U.S. for over a century and it has only covered 1/3 of the area where extensive impacts are likely to occur once infested. Minnesota has thousands of acres of prime host trees for gypsy moth to munch on.
Photo courtesy of Garrett (MD) County Extension Office

5. Human Nuisance
In addition to being detrimental to tree and forest health, gypsy moth infestations can have impacts on humans. Large numbers of caterpillars may be intolerable and can negatively impact tourism and outdoor recreation. Tiny hairs from shed skins can provoke rashes and respiratory ailments in sensitive people.
Property values may drop due to tree decline and death; trees planted for timber may suffer stunted growth after repeat defoliations. Gypsy moth is a federally regulated pest and quarantine restrictions require costly inspections (mills, lumber companies, nurseries, movers).
The top photo shows hundreds of caterpillars crawling over a home. The picnic table in the bottom photo is covered in leaf fragments, shed caterpillars, and frass; not pleasant for outdoor dining. Burlap bands around individual trees can indicate where gypsy moths hide during the day to avoid predators.

6. Where is Gypsy Moth Established?
Europe and north Africa (native)
U.S. and Canada (invasive)
Apart from its native range in Europe and northern Africa, gypsy moth has gained a foothold in North America. It was introduced to Medford, Massachusetts in 1869 and now, 140 years later, has established itself west to Wisconsin and south to North Carolina. Canadian officials have found gypsy moth in several provinces. Normally, entire counties are designated as infested, but Maine regulates by township, resulting in their “partially regulated” status.

7. Identifying Gypsy Moth
Egg Masses
Caterpillars
Pupae
Adults (males vs. females)
Unlike the other invaders you have been/will be hearing about today, gypsy moth is associated more with the leaves than the bark of trees. To identify gypsy moth correctly you have to know 1)what time of year is it? 2)what time of day is it? and 3)what is it doing?
We will go over the four stages of development the gypsy moth goes through during its 1-year-long lifetime.

8. Gypsy Moth Life Cycle
The gypsy moth has one reproductive cycle per year, and the life stages are synchronous which means that they are all hatched about the same time, molt about the same, etc. As you can see, most of their year is spent in an egg mass. This chart is geared toward the life cycle in Minnesota; if you go to Virginia or North Carolina you can catch eggs hatching in April and adult moth activity is wrapped up by August.
Let’s go through these stages one by one…

9. Egg Masses (laid in late summer, hatch in late spring)
Each female lays one mass containing eggs
Overwinter in a protected spot
Eggs are laid in August or September in a fuzzy, buff-colored mass which are about the size of a quarter. The fuzz is actually hairs from the female’s abdomen that she uses to insulates the eggs and protect them from parasites and predators. Each egg mass contains between eggs which will hatch in late spring. Females will lay their egg masses on tree trunks and branches, on automobile wheel wells, on outdoor household articles or almost any convenient surface. This is what makes them so hard to find sometimes.
Emergence

10. Spot the Egg Mass
This egg mass was very well camouflaged on a tree with peeling bark, lichens, and fungal growths. Lucky for us, it was at eye-level facing a walking trail. Egg mass searches in rural areas or forests can be very difficult!

11. Caterpillar (late spring through early summer)
First instar larvae
6 pair of red spots
5 pair of blue spots
Newly-hatched caterpillars are about 1/8” long, hairy and mostly dark brown to black. They say that eggs hatch when an oak leaf is the size of a squirrel’s ear if that’s helpful to you. The caterpillars are voracious feeders and can grow to 2” in length. As they grow, their markings become more evident--five pair of blue spots and six pair of red spots along their backs. They typically feed in the treetops at night but migrate down the trunk to the ground each day as protection from the heat and birds.
Larger caterpillars rest by day, eat at night

12. Caterpillar Lookalikes
Spiny elm caterpillar
fg = 2”
Whitemarked tussock moth
fg = 1 1/3”
Eastern tent caterpillar
fg = 1 3/4”
Gypsy moth, fg = 2”
MN Dept of Ag.
Here is a look at some caterpillars that often get accused of being gypsy moths. Many of them are gregarious, they are found in large groups like the gypsy moth, but see if you can tell what sets the gypsy moth apart. Remember the colored markings on the back, the absence of a web, and the host tree it is feeding on.
Fall webworm, fg = 1”
Yellownecked caterpillar
fg = 1 3/4”
Forest tent caterpillar
fg = 1 3/4”
Whitney Cranshaw

13. Feeding Damage Entire leaf to midrib Can cover acres of woody habitat
Gypsy moth caterpillars are very messy eaters. Some caterpillars eat leaves systematically but the gypsy moth seems to feed indiscriminately, a bite here and a bite there. They will eat the leaf tissue right down to the midrib. In high populations, these hungry caterpillars can move through the treetops and quite rapidly defoliate huge tracts of forest.

14. Host Preference Preferred Less-preferred Avoided
eaten by all stages of larvae
Oak, aspen, willow, white and river birch, basswood, larch, mountain-ash, alder and apple
Hawthorn, hazelnut, hophornbeam, hornbeam, serviceberry, witch-hazel
Less-preferred
eaten only by older larvae
Yellow birch, boxelder, butternut, black walnut, cherry, eastern cottonwood, elm, hackberry, hickory, red and sugar maple, pine, and spruce
Blueberries, pin cherry, chokecherry, sweet fern
Avoided
rarely fed upon
ash, cedar, fir, silver maple, catalpa, mulberry and many urban species
Dogwood, elderberry, grape, greenbrier, juniper, raspberry, viburnum, and buckthorn!!
The gypsy moth caterpillars can consume about 9 square feet of foliage as they develop. The species of choice for feeding are oak, aspen, willow, white and river birch. Younger larvae will develop best on the preferred species; however, as they get older they can tolerate some of the less-preferred woody species.

15. Pupa (Cocoon) (summer months)
Males smaller than females
Sparse silken threads
Found in protected spots
Bark crevices
Duff layer
2 weeks
After feeding for 5-6 weeks, gypsy moths pupate to transform from caterpillars to adult moths. The pupa is hairless and you can see that it only uses sparse silk strands to keep it attached. It is dark reddish-brown and leathery, and ranges from ¾” to 1 ½” long and ¼” to ½” wide. Females are larger than males as you can see in the photo. Pupae are usually found in crevices in the tree trunk or on larger branches, however, they also love to hide in tree collars, on fences, or really any solid substrate.

16. Adult (mid-summer to early fall)
Female
(does not fly)
Feathered antennae
After about two weeks in the cocoon, the adults emerge. Adults do not feed and there is only one other thing to focus on—mating. Females cannot fly so they simply crawl to an open area to release their pheromone. The males are intent on picking up that scent and are strong fliers so will flutter about for about two weeks to find a female.
Distinct “commas” on both top and underside of wings
Male (daytime flier)

17. Mating Behavior Females do not fly Pheromone attracts males
Females lay one egg mass
Adults die, eggs overwinter
This (**animated**) slide depicts the mating behavior of the gypsy moth. It is extremely important to know about both insect life cycle and behavior when developing a management plan. Gypsy moths have been in this country for 140 years so we have gained tremendous knowledge about both.
The female gypsy moth does not fly but must mate to fertilize eggs for the next generation. She emits a pheromone into the air from where she is and waits. The males are strong fliers and can sense the pheromone from up to a mile away. They follow the pheromone plume back to the female and mate. The female lays eggs and both the adults die shortly thereafter, leaving the eggs firmly attached to overwinter.