Although very common in the United States, the Gypsy moth—one of the most damaging insects to our forests—actually originated in Europe and Asia and was brought to America by a French scientist. When the species was accidentally released in the late 1800’s, few people could have imagined the results. The Gypsy moth is fairly nondescript and doesn’t look like it could cause much harm, but every year millions of dollars are lost as Gypsy moths do unparalleled damage to economically important forests (primarily oak trees.) Ironically, the adult Gypsy moth does not do the principle damage to the forestry, but rather it is the larvae/caterpillar that is causing the irrevocable defoliation.
Gypsy Moth Life Cycle
Because such a large amount of the Gypsy moth’s life is spent as larvae, it is important to understand the different stages of life and how these stages can make the species very dangerous, economically and environmentally.
The female Gypsy moth in the United States are flightless; this is significant because unless the eggs are moved by the wind or carried by humans or animals, each generation of the moth will continue to feed on one tree.
Immediately after emerging from her cocoon, the female Gypsy moth will lay her eggs (which can range from under 100 to more than 1000) on the branches or trunk of its host tree. Again, she cannot fly and so at most she will be able to climb up a limb or branch.
The egg sacs are small, less than an inch in length.
The eggs can survive through winter and therefore a freezing climate stop the Gypsy moth life cycle.
The caterpillar will usually hatch in mid-spring.
Each larva has vital growth periods known as instars. Male Gypsy moths have five instars and females have six.
During the first few stages, the larvae will feed on the surrounding leaves. In the later stages, the larvae feed on the higher leaves and the bark.
The damage caused to the trees depends on the number of larvae hatched that season. If a high number of larvae, the caterpillars will feed continuously day and night. If there are low numbers, the caterpillars will only feed at night.
Pupation and Adulthood
After about two months the caterpillars form cocoons where they will remain for one to two weeks depending on the season.
Once they emerge the adult Gypsy moths will only live a short time; their sole goal will be to mate and reproduce in this finite period of time.
The males are a mousy brown and generally come out of the cocoon first. While waiting, the males will eat both day and night on their host tree.
When the females (black and white in color) break free of their cocoon, they will already be carrying eggs and only require a brief mating session with the male to complete the process.
Because female Gypsy moths remain flightless during their short adult lives, their eggs will be dropped near their mother’s cocoon and the cycle will start all over again.
Gypsy Moth Damage
Despite their short lives, the Gypsy moth thrives on one of the United States’ most important commodities: trees. Almost since their introduction, Gypsy moths and U.S Government have been working against each other. Fighting a battle over environment and territory, each year the Gypsy moth stays one step ahead as it continues to expand its habitat and reproduce.
The majority of trees affected are in the eastern United States where host trees are generally oaks or aspens. Gypsy moths perform what is known as defoliation on the trees; the moths will strip the trees of their leaves. While this may not seem a major factor, forestry experts understand that this makes the trees weak and prone to disease. If this happens on a year-to-year basis it will increase the trees’ mortality rate. If the defoliation is extremely bad one year and there are other environmental factors involved (flooding, drought, termites, storms, etc.,) then there is a high probability that the tree will die that same year. The Gypsy moths work and move quickly; it is possible for them to defoliate an entire forest over the space of a few years. The Gypsy moth has deforested more than a million acres of U.S. forestland alone.
Gypsy Moth Control
The U.S. Government and local forest conservation groups are working to produce an effective method for eradicating the Gypsy moth from U.S. forests. The Gypsy moth does have natural predators such as mice and birds, but these predators do not consume enough to keep the Gypsy moth under control. Recently, efforts have been made using a fungus that is able to deter the moth. Questions still remain regarding the cost to mass produce the fungus and its effectiveness over large areas is not known. Currently, the only proven preventative method is pesticides which are sprayed over forestland every year. It is virtually impossible to cover every inch of land and so it remains to be seen who will win the battle: moth or man.