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Below please find information from our Tree Warden, Tom Chamberland, concerning the Gypsy Moth.
As predicted last year, they are back, with a building population, the Gypsy Moth caterpillar (Lymantria dispar). 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. 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. Again, as in last year, my phone has been ringing off the hook, with inquires about our current gypsy moth infestation. Current infestation does not seem to completely cover Sturbridge Holland and Brimfield, however expansion is likely, so 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-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. Each of the 11 sections of a developed caterpillar will have two colored spots, the first five pairs, blue, and the last six, red. 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. In this first full week of June we are entering the 2nd and starting the 3rd, moulting stage. 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 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 spruces. Gypsy moths appear to dislike ashes, sycamores, butternuts, black walnuts, dogwoods and balsams. 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 almost complete defoliation. Last year’s infestation experienced pockets of 50% - 75% defoliation. 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.
When egg mass densities reach very high levels of over 1000 masses per acre 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.
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. 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 at least in North America 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. has a high specific mode of action 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; and is more effective during wet, raining periods therefore, larval mortality is not immediate and may take up to ten days for mortality to occur. Generally, proper timing is critical since the larger caterpillars are harder to kill, B.t. usually causes the collapse of outbreak populations, but this may take two or three years to accomplish through a natural build up in the environment.
Management:
We can take some proactive steps to control the gypsy moth the 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. To prevent the caterpillars from reaching the foliage, some may recall the use of a 6” wide 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, including the “good bugs” we may want around our yards. Thuricide is the common name for a Bt based product. Other more general purpose insecticides will ha Imaclopred as its active ingredient. Use an insect spray at the first sign of the caterpillars, and repeat the spraying every two to three weeks. If you want to address your larger trees, you will need to contract with a professional licensed pesticide applicator, and while a whole tree spray will help, due to the life cycle of the gypsy moth, at least two applications may be necessary for good control. Due to the wide spread nature of the gypsy moth, and the effectiveness of natural controls the along with the cost, environmental and private property access considerations wide area aerial
spraying is not an option for controls of the gypsy moth.
On Going Research:
The gypsy moth has been intensively studied over the last 100 years in North America. 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 and others. To find out more on the gypsy moth visit: http://www.invasivespeciesinfo.gov/animals/eurogypsymoth.shtml
We survived the 1980’s infestation, as we most likely will this one. They are definitely a nuisance, with their chewing noise and droppings, so extra effort to clean up your outside patio area before use is recommended. It has also been reported that some people have skin sensitivity to the Gypsy Moth, so always wear gloves and long sleeved shirts when handling the insect or its heavily infested area.
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