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I asked our Tree Warden (Tom Chamberland) to prepare some information regarding the upcoming gypsy moth infestation. As you know, last year was a terrible year for the pecky insect and this year has the potential for the same. Attached is a photo of a pypsy moth laying eggs and a treatment option page.
Yes, with a building population, the Gypsy Moth caterpillar (Lymantria dispar) continues to infest our yards in the Sturbridge area. The gypsy moth is one of North America's most devastating forest pests. Like the tale of the sorcerer’s apprentice, the gypsy moth is an example of an experiment gone horribly wrong. The moth was brought to the United States in 1869 in a failed attempt to start a silkworm industry by E. Leopold Trouvelot escaped. About 10 years after this introduction, the first outbreaks began near Boston and in 1890 the State and Federal Government started their attempts to eradicate the gypsy moth. These attempts ultimately failed and since that time, the range of gypsy moth has continued to spread throughout the eastern United States. Here in the Sturbridge area our last severe outbreak of Gypsy Moth occurred in the mid 1980’s, which older residents may recall. Over the last two years, with a building population, and with inquiries about our current gypsy
moth infestation, here is what you need to know.
Identification:
Gypsy moth caterpillars start as a tan or light brown egg mass, laid by the white colored female moth from mid-July thru September, and usually hatch by mid-to late May, timed with the leaf expansion of our deciduous trees. Gypsy moth caterpillars change appearance as they grow. Young caterpillars are black or brown and about ¼ inch (.6 cm) in length. As they grow, bumps develop along their backs along with coarse, black hairs. Mature caterpillars can be as long as 2 ½ inches (6.35 cm).
The Life cycle:
Tree damage is caused by the insect larvae feeding. The larvae move to the leaves of trees and begin to eat, mostly at night. During daylight hours, larvae generally seek shade from the sun but feeding can occur in daytime in heavy infestations. Gypsy moth larvae grow by moulting, five moults for males and six for females. Feeding occurs in the “instar” stage or period between each moult. As might be expected, a caterpillar’s appetite increases with each moult. Feeding continues until late-June into early July when the caterpillar enters the pupal stage emerging, finally, as a moth. Both male and female moths exist only to reproduce once with the brown colored male moths flying to find the white colored females who are too
heavy to fly. After the females lay their eggs from July to September, moths of both sexes then die.
Effect on our trees:
The gypsy moth caterpillar is not a fussy eater. It has a preference for the leaves of deciduous hardwood trees such as maple, elm, and particularly oak. Gypsy moths can also feed on apple, alder, birch, poplar and willow trees. As it grows it will also attack evergreens like pines and hemlocks. However, during heavy infestations, competition for food will drive the caterpillar to attack almost any tree or shrub as we witnessed back in the mid 1980’s. Depending on the degree of infestation, tree damage ranges from light to complete defoliation. Last year’s infestation experienced a 75% defoliation on some trees and areas of town. Most deciduous trees can survive a moderate degree of repeated defoliation. Many can even
survive one complete defoliation by the gypsy moth caterpillar. However, continuing attacks can fatally weaken a tree or leave it vulnerable to other insects or disease. Last summer’s drought was not good for those trees affected by the gypsy moth.
It has been speculated that our continued spring droughts (the last 4 springs) will cause Gypsy moth populations to erupt into egg mass densities to over 1,000 per acre. When densities reach those very high levels, trees become completely defoliated. Several successive years of defoliation, along with contributions by other biotic and abiotic stress factors, may ultimately result in tree mortality. At the lower densities, we hardly realize they are around.
Natural Enemies:
A variety of natural agents are known to kill gypsy moths in nature. These agents include over 20 insect parasitoids and predators that were introduced over the last 100 years from Asia and Europe. However, the density of these predators respond to the density of the gypsy moth. With the last three years increase in gypsy moths, we are starting to see an increase in these parasitoids, but there is a lag time. Small mammals are perhaps the most important gypsy moth predator, especially at low population densities. Birds are also known to prey on gypsy moths but this does not substantially affect populations. The biological insecticide Bacillus thuringiensis, (B.t.) is among the least toxic insecticides for use in residential areas to control the gypsy moth.
Its active ingredient is a bacterium which occurs naturally in the environment. B.t is good in controlling caterpillars and has shown no toxicity to mammals, fish of other wildlife at the recommended field rates. B.t. must be ingested by the gypsy moth caterpillar to be effective; therefore, larval mortality is not immediate and may take up to ten days for mortality to occur. Generally, proper early stage timing is critical since the larger caterpillars are harder to kill, B.t. has been known to cause the collapse of populations, with a return to normal or better, above normal rainfall in the months of May and June will help and potentially cause a natural collapse.
Management:
We can take some proactive steps to control the gypsy moth egg and larval (caterpillar) stages. Egg masses, when discovered, should be removed and soaked in water (look for them on your trees, walls, fences building from mid-July thru September). If the egg masses are unreachable, spray them with a strong dose of Horticultural Oil Insect Spray. Spray in the late fall as well as a few times in the early spring, before leaves begin to form on trees. Once gypsy moths hatch, to prevent the caterpillars from reaching the foliage, apply a tinfoil band wrapped tightly around the tree covered with a layer of grease. If you choose this method, it can get messy, and never place grease directly on a tree bark, always cover with tinfoil first. There are also several “over
the counter” sprays and moth traps that are effective, but remember, as with B.t. and any other spray it is non-selective, so not only will it kill the gypsy moth, but any other caterpillar or similar insect. Use an insect spray at the first sign of the caterpillars, and repeat the spraying every two to three weeks. If you want to spray or treat your larger trees, you will need to contract with a professional licensed pesticide applicator, and choose a whole tree spray or soil injection of the pesticide immacloprid, a non-selective insect control pesticide. Due to the life cycle of the gypsy moth, at least two applications may be necessary for good control. “Cross contamination” by gypsy moths from untreated trees will need to be monitored, and may reduce the effectiveness of any chemical control. Contact Certified Arborist tree care companies now to get on their treatment schedule. All local garden centers are now carry BT, Dormant oil, and residential use
Immacloprid insecticide.
Clean up:
The droppings from feeding caterpillars and leaf litter, can be quite messy. The best way to clean a deck, patio or walkway is during dry weather with a leaf blower to remove accumulated frass. Remember to wear long clothes, eye, face and ear protection.
Town’s Response:
Due to the wide spread nature of the gypsy moth, the effectiveness of natural controls, along with the cost, legal, and environmental considerations the town cannot spray or any other control of the gypsy moth now. There is no state funding for any control.
On Going Research:
The gypsy moth has been intensively studied over the last 100 years. Currently there are numerous groups around the country investigating various aspects of the biology, ecology, and management of the gypsy moth. This work is funded by the USDA Forest Service. To find out more on the gypsy moth visit: http://www.invasivespeciesinfo.gov/animals/eurogypsymoth.shtml
They are a nuisance, with their chewing noise and droppings, so extra effort to clean up your outside patio area as suggested is recommended. It has also been reported that some people may have skin sensitivity to the Gypsy Moth caterpillar itself, so always wear gloves and long sleeved shirts when handling the insect or its heavily infested area.
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