Forest Tent Caterpillar

Forest Tent Caterpillar has extensively defoliated trees in Onondaga County in 2005 and 2006. More to come?

FOREST TENT CATERPILLARS

Natural History
They have beautiful colors and patterns, but they come in such astounding numbers that their beauty is often lost on us. Known for their voracious appetites, forest tent caterpillars can be identified by their bright bluish-green bodies with a black stripe that is covered with a single row of white spots.

In the Northeast, adult moths lay their eggs on sugar maples and red oaks. The eggs are coated in a hard, glue-like substance that allows them to survive harsh winter conditions. The egg mass is squarish at each end, in contrast to that of the eastern tent caterpillar which has more tapered ends. The caterpillars emerge in the spring around the time that trees in the forest are beginning to leaf out. The timing isn’t coincidental; the caterpillars are ferocious feeders for two months, and may completely eat through the leaves of entire trees. Groups of caterpillars often leave the sugar maples or red oaks they were born on to feed on the leaves of a variety of hardwood trees.

Unlike the Eastern Tent Caterpillar, the Forest tent caterpillar doesn’t quite live up to its name. Rather than building tents, the caterpillars lay down a silken pad on leaves where they congregate. Scout caterpillars that are looking for new sources of food will also lay down silk trails that signal to other members of the group where a new food source is located.

After about two months, individual caterpillars form cocoons in folded leaves. Adult moths emerge about three weeks later. Shortly after, moths lay their egg masses and die.



Damage
The relationship between forest tent caterpillars and trees is a natural one. Most trees can survive occasional bouts of caterpillar damage. Even trees that have lost all of their leaves respond by growing new leaves shortly after being defoliated. However, trees that are repeatedly attacked, or that are further stressed by factors such as drought in the summer, may lose branches or eventually die. Sugar maples may produce less sap or sap with a lower sugar content as a result of just one year of leaf loss.

Records show that Forest Tent Caterpillar outbreaks occur in NY every ten to eleven years. Outbreaks may last several years, depending on many factors, including weather. In 2005, caterpillars defoliated 650,000 acres in NY, and at least 80,000 acres in Central New York . This is the largest forest ten caterpillar outbreak in NY since 1953. The current outbreak, which started in 2002 in St. Lawrence County, appears to be winding down.

By the time we see them moving around much damage has been done to the host tree. Control is most effective before or just after hatch.

Natural Controls
Larger and slower than a house fly, Sacrophaga aldrichi is an important predator of the forest tent caterpillar. The adult fly deposits live maggots on caterpillar cocoons. The maggots move into the cocoons, bore into the pupae and feed on them. More caterpillars mean more food for the flies, and growing fly populations eventually help to curb forest tent caterpillar outbreaks. If you had a large caterpillar infestation followed by annoying flies, the “friendly fly”, be optimistic that you infestation will be low this year.

Mild winters can work against the caterpillars, as warm winter weather often prompts caterpillars to emerge before trees have leafed out. Without a food source, early emerging caterpillars may starve before the first leaves appear. Extremely wet and cold conditions in early spring also play a part. Viruses and a bacterial disease known as “wilt” can also reduce caterpillar populations.

Count Egg Masses to Assess Potential for Defoliation Next Year


New York State DEC has a protocol for sampling egg mass numbers that you can use in your woods or neighborhood. Data collection instructions, form and interpretation form (pdf, 230 KB). Contact CCE Onondaga for more information (phone and email information below).

Treatment Options
Homeowners could remove egg masses from small infested trees before caterpillars emerge in the spring. The current year’s egg masses are shiny and appear to be varnished. This can be a difficult option for large trees as the egg masses tend to be in the top third of the canopy.

Best control is before eggs hatch (mechanical) or when the caterpillars are small before they have done serious damage (insecticide sprayed on foliage and ingested by the caterpillars). Bacillus thuringiensis subsp. Kurstaki and aizawai are effective biological insecticides. Chemical options are acephate, carbaryl and malathion. Apply to foliage when redbud blooms in your neighborhood. Treating large trees is best done by a tree service. Aerial application is possible and the best option for large wooded tracts.

Sticky barriers can prevent migration of caterpillars up a tree or keep a cohort of caterpillars from leaving one tree for new forage. Tie a 4-6” wide strip of craft paper or burlap around the tree then spread a sticky substance such as Tanglefoot® on the material. The caterpillars will not cross the barrier. This will not prevent damage to the tree from caterpillars that hatch in that tree, but they will be unable to leave the tree to damage others.

Removing the caterpillars when they congregate on tree trunks is a satisfying option, but much of the damage is already done.

For larger trees in residential settings, consult with a certified arborist about treatment options. Visit the New York State Arborists website to find a local certified arborist. Follow the menu to Consumer Information and the Membership Directory.

Landowners with large areas to treat may want to look at the NYS Department of Environmental Conservation website for a list of Aerial Pesticide Applicators registered with NYSDEC.

Hiring a pesticide applicator
Visit the U.S. Environmental Protection Agency website for tips on hiring a pesticide applicator

EASTERN TENT CATERPILLARS:
Will the Real Tent Makers Please Step Forward?


Natural History
Of the two ‘tent’ caterpillars in NY, it is only the Eastern tent caterpillars that are actually tent makers. They are dark in color, with a white stripe along the back and a row of oval, pale blue spots on each side.

Adult moths lay a mass of eggs that encircles the twigs of plants. Like the egg mass of the Forest tent caterpillar, this insect covers its eggs in a shiny, glue like substance.

Caterpillars emerge in early spring when the first leaves begin to appear on trees. They make conspicuous silken tents in the crotches of trees. Caterpillars that emerge from a single egg mass stay together in the same tent, expanding the tent as they grow larger. Tents are filled with black spots of excrement and molted skins.

Caterpillars feed on the leaves of black cherry, choke cherry and scrub apple. They may also defoliate other fruit trees as well as deciduous forest and shade trees including birch, oak, willow, poplar, and beech.

In six or seven weeks each larva spins a whitish cocoon that is filled with a yellow powder. Adult moths emerge after 10-14 days.

Treatment Options
Destroy worthless apple and wild cherry trees to help reduce infestations of eastern tent caterpillar on neighboring trees. Homeowners can remove and destroy tents in early spring during daylight hours when the caterpillars are in these shelters. Removing egg masses before caterpillars emerge is also an effective way to reduce populations on small trees.

Hiring a pesticide applicator
Visit the U.S. Environmental Protection Agency website for tips on hiring a pesticide applicator

References/Links
Cornell University IPM Newsletter
New York State Department of Environmental Conservation
Penn State Entomological Notes
SUNY ESF
SUNY Cortland
Digital Librarian