The usual moth life cycle has four stages. Moth eggs hatch into immature insects called larvae; for moths and butterflies they are better known as caterpillars. The caterpillar molts or ‘sheds its skin’ to increase in size. So the caterpillar stage is divided into substages and the different sized caterpillars are called instars. The instars are designated as 1st instar, 2nd instar, 3rd instar, 4th instar and 5th instar. These instars feed over a period of five to six weeks. The 5th instar stops feeding altogether wandering about looking for a place to spin a cocoon. Surrounded by the cocoon, the caterpillar molts to the pupa stage. The inactive pupa does not feed while undergoing changes to become an adult. The adult insects live less than a week to mate and the females lay eggs.
Now for a more detailed view of the forest tent caterpillar life cycle. The eggs ‘hatch’ into minute caterpillars within three weeks but the caterpillars will bide their time within the egg mass to overwinter. In spring as leaf and flower buds begin to unfold, the caterpillars leave the egg mass and begin feeding. The caterpillar is the feeding machine. These social caterpillars coordinate their movements on one branch of the tree with pheromones (chemical scent) deposited along the strand of silk produced by individual caterpillars. As individuals return from a good feeding site the stronger scent produced directs the others to food. When not feeding the caterpillars gather on the branch or trunk on a silk pad to rest and molt before moving out to the food source. The caterpillar prefers sugar maple and aspen or ‘popple’ here but may eat a variety of hardwoods except red maple. It does not eat conifers. As they consume leaves, more waste material is eliminated than nutrients are utilized. The droppings known as frass can be heard as they rain down from the tree branches to the ground.
If the food supply in the tree runs out, the caterpillars move on together in search of food. On the ground, coordination among the caterpillars may be lost; a terrain of grasses and herbs presents a confusing landscape for the dispersing older instars. Many caterpillars may wander off and simply starve to death if no suitable food is found. Others succumb to natural diseases caused by viruses and fungi. By the last instar the caterpillar has consumed many times its original weight in food. Now the caterpillar stops feeding and begins the search for a suitable sheltered place. It’s also the time to eliminate the remaining frass from the gut. Full-grown caterpillars about two inches in length find their way onto roads, driveways, houses and outbuildings. Feeding is over. It’s time to make cocoons.
After twenty-four hours with the pale yellow silk cocoon successfully spun, the encased caterpillar molts to become a pupa. An examination of a pupa reveals a very different looking insect with the compound eyes and antennae on the head and the wings and legs of the adult closed pressed around the body. It would be during this stage that fly and wasp parasites are common. During caterpillar outbreaks, the common native insect dubbed the ‘friendly fly’, seeks out cocoons and deposits a live maggot on the cocoon. The maggot burrows in to feed on the pupa and eventually kill it. The pupal stage lasts about three weeks in June.
In early July the surviving pupae emerge as adult moths. Males seek out the females using the female pheromones and visual cues. After mating, the females move to the host trees to deposit all their eggs in a single batch of about 150 eggs on a twig in the upper third of the crown of the tree. The egg mass completely encircles a twig in the upper crown of the tree and eggs are covered with a shiny shellac-like layer. The egg mass has a distinctive shape in that the ends of the cylinder that surround the twig are straight. These half-inch egg masses on twigs are the objects sought for a count when winter monitoring is used to predict possible outbreaks of the caterpillar in spring. Unable to feed, the moths are short time visitors in the forests. The cycle continues the following spring when caterpillars emerge to feed.
NUISANCE
Two basic strategies should be adopted: First, identify the trees or buildings that you want to protect. Then work to protect the things you selected and ignore the rest (or at least try to). It takes a lot of time and energy to try to protect everything on your property. Second, be persistent. Some treatments may require daily monitoring or retreatment.
How can I keep them off my house, patio, lawn furniture, etc.?
1. Brush caterpillars off the house with a stiff broom or knock them down with a stream
of water. If possible, do this daily. Avoid squashing caterpillars on the house. Clean off
lawn furniture, patios, decks, screens, etc. with either of these two methods. The longer
caterpillars sit on painted surfaces, the more difficult it is to remove stains.
2. Dispose of dead caterpillars by burying them or mixing them into the compost pile.
3. Cocoons are difficult to remove by water pressure. Brush them off the house with a
stiff broom. Bag, burn, or bury the cocoons.
REDUCE DEFOLIATION
While maple and other hardwoods are the preferred hosts, FTC will feed on any broad- leaved tree except red maple. In forests, outbreaks usually collapse before tree damage occurs. FTC can consume 60% of a tree's foliage for 2 to 3 years without ill effect. In the suburban landscape, the situation is a little different. First of all, the trees are much more valuable and secondly, they are apt to be subjected to many other stressing agents (soil compaction, construction damage, other insect and disease pests, lawn herbicides, etc.). So trees in your yard may be at a greater risk of damage than forest trees.
How can I tell if my tree(s) are at risk?
1. Defoliation of birches and oaks makes them vulnerable to stem boring insects. If your
birches or oaks have suffered 2 years of heavy defoliation or have branch tieback, then
treatment to prevent defoliation could be warranted.
2. Newly planted woody ornamentals and tree saplings are very vulnerable to any type of
stress and with the loss of leaves, some may be killed.
3. The production from fruit trees, raspberries, strawberries and other fruit and vegetable
crops will be greatly reduced or lost if moderate defoliation occurs.
4. Shade trees and ornamental shrubs are vulnerable if they have been recently damaged
by construction, trenching, soil compaction, blacktopping, etc.
5. Drought stressed trees are also at risk when defoliated or attacked by stem borers.
What can I do to protect my trees, shrubs and garden from heavy defoliation?
1. Before they hatch (any time from July of last year to early-May of this year) hand pick
all the egg masses off of valuable plants. Destroy or dispose of them.
2. Hand pick caterpillars off plants and dispose of them. A bucket of detergent water is
an effective collection container.
3. If there are no egg masses in a tree or if you have sprayed the tree, you may prevent
migrating caterpillars from climbing up the trunk by the use of barriers. Construct a
barrier band around the trunk made of duct tape, plastic, or tar paper and coat it
generously with grease (Tanglefoot or Vaseline). Never apply grease directly to the tree
bark. Place the barrier band in the shade or you risk killing the bark and cambium under
the band. Check daily to see if more grease or Tanglefoot is needed. Remove the band in
early July after the caterpillars form cocoons.
4. Spray an insecticide to kill caterpillars. Each product has restrictions as to which
plants and sites where it can legally be applied. If applying to shade and ornamental trees,
the label should say it is for use on shade and ornamental trees. Please read and follow
label directions.
.. Biological insecticides containing Bt, (a bacterial product made of Bacillus
thuringiensis) are the recommended products because of their safety and the low
toxicity to non-target organisms. These Bt products are only toxic to caterpillars;
they do not kill bees and flies. However, Bt products are slightly slower to act
since they must be eaten by caterpillars before they take effect. Apply Bt to the
leaves of host plants not to the bark or other non-edible materials. It is most
effective on young (small) caterpillars.
.. Insecticidal soaps can be sprayed directly onto caterpillars or onto plants they
infest. Insecticidal soaps are insecticides made from naturally-derived fatty acids.
Repeat applications may be necessary.
.. Chemical insecticides are a second choice after Bt, due to safety considerations.
Commonly used chemical insecticides can also kill bees and other organisms, so
exercise caution when using them.
5. FTC moths are attracted to lights during early July. Turning off outside lights may
reduce egg-laying on your trees and reduce next year's population.
Can I do anything to help defoliated trees and shrubs?
1. The most important thing you can do for your trees is to keep them well watered.
Supply 1 inch per week if you do not receive that much in rainfall from May 1 through
September 1.
2. Do not fertilize trees or use a weed and feed product on your lawn during an outbreak.
Heavy nitrogen fertilization encourages the tree to produce more leaves which may
deplete energy reserves causing additional stress to the tree.
3. Stressed trees are easily attacked by other serious insect or disease pests. You may also
need to protect trees from these pests as well.
Are there any long-term solutions?
FTC have cyclic outbreaks with about 10 years between population peaks. One long-term solution to defoliation and nuisance is to maintain tree vigor. Maintain tree vigor between outbreaks by watering, fertilizing, properly pruning trees and by avoiding root and trunk damage. Another method is to plant trees that are not preferred food hosts. If most of the trees in an area are not hosts for FTC, then fewer caterpillars will be found there. Foliage of red maples and most conifer species is not eaten by FTC.
This information was adapted by Mary S. Rutley for New York State from a homeowners tip sheet on the Minnesota web site on forest tent caterpillars.
Bacteria are present everywhere in our natural environment, including in soil, in food and even on our skin. Bacillus thuringiensis (Bt) is a bacterium that is found naturally in the soil and is known to cause illness in various insect larvae, including caterpillars of pest species such as gypsy moth, spruce budworm and cabbage looper. There are more than 20 varieties of Bt. The "kurstaki" strain (Btk) is used for caterpillar control and other strains are used for black fly and mosquito control. It is not harmful to humans, birds, pets, fish, honey bees, beetles, spiders, and other nontarget organisms.
Is Btk safe for humans? Bt has no known toxic effects on humans or other mammals, plants, birds, fish, honeybees, or other beneficial insects. Its safety record, and the results of more than 30 years of Bt investigation around the world, have led many countries including Canada, the United States and most other countries where Bt products are currently registered to declare it exempt from pesticide residue tolerances on food crops.
Btk is used to control pest caterpillars in the production of many food crops. Organic food growers also use this biological insecticide. Unlike many pesticides, Btk can be used right up to the time of harvest because it is not toxic to humans if eaten. Any sprayed fruits or vegetables should be washed before they are eaten.
Even though there is no evidence of harm to humans from Btk, persons with respiratory ailments or other health concerns may wish to reduce their exposure to the product during the spray operation. To deal with this, close windows the evening before aerial spraying takes place and stay indoors until the Btk product has had time to dry (which takes a few hours).
The spray does not cause damage to automobile, house, boat or trailer paints or finishes. If it is left to harden, the spray can be removed with water but may require more effort. The sooner it is washed off the easier it is to remove.
How does Btk work? Btk affects only the larval stage of susceptible insects; it cannot be used to kill eggs, pupae, or adults. To work, Btk must be eaten by the caterpillar. Btk will not harm caterpillars if it remains only on their skin. Once inside the caterpillar’s stomach, where a basic (alkaline) pH is present, the protein crystals break down. Specific enzymes in caterpillars’ stomachs are also required to activate the product. When the Btk is activated, the gut is paralyzed and the caterpillar stops feeding and dies within one to five days. Larvae are most susceptible to Btk when they are in the early developmental stages.
How long does Btk last in the environment? Btk breaks down quickly in the environment in about three to seven days. Sunlight will help to break the product down. For the most effective use of Btk, it is usually applied more than once in infested areas. This is because the caterpillars must be in an early larval stage in order for the Btk to work. Unfortunately, not all caterpillars hatch at the same time. Because the product breaks down quickly, it will not be available to caterpillars that hatch after the first spraying, unless repeated applications are made.
Will the pests develop resistance to Bt? After 25 years of use, there are no known instances of these target insects developing resistance to Bt.
How are Bt products made? The bacterium is grown in sterilized tanks, on an artificial diet mix. The bacterial solution is mixed with water or a mineral oil similar to baby oil to form the end product. The manufacturer then adds a proprietary mixture of inert ingredients that aid in improving the effectiveness of the formulation. These ingredients include stabilizers, stickers, UV protectants and preservatives - all are considered of minimal risk to human and environmental health by Canadian and U.S. pesticide regulators. Caterpillar eradication programs only use the water-based formulation.
The above information was obtained from Ministry of Forests and Range, Government of British Columbia, Canada web site.