Arborvitae and junipers are not the most desirable host plants for gypsy moths. Oaks are it's favorite hosts. Gypsy moths feed on most evergreens only after the moth population has generally reached epidemic proportions for a given area and most other plants are already heavily infested. With heavy feeding, gypsy moth can kill the evergreens.
The male gypsy moth is brown to dark brown in color and can fly. The female moth is almost pure white (there are some black bands across the leading edge of her front wings and is unable to fly. Her body size or mass is too much weight for her wings to lift. She must crawl to whatever elevated location she chooses for laying her eggs. The egg mass is light brown or buff color and looks a little fuzzy.
When the eggs are laid on vehicles and outdoor toys, patio furniture and other outdoor goods being moved from one area to another, the gypsy moth population is often expanded into non-infested areas. The eggs hatch into caterpillars. Egg hatching varies depending on weather for your location. The caterpillars are hairy and can be of different coloring depending on population density. Dark-colored individuals occur when the population is not very dense. Young larvae suspend themselves from leaves on thin silk. Strong winds carry the larvae long distances, while the larvae are attached to this thread. The larvae feed for about seven weeks before pupating. The pupation period is another stage when gypsy moth can be moved long distances such as when people are moving or vacationing. The pupa is a brownish - black case. Several weeks later, adults begin to emerge.
The adult males are out several days before the female. The male can "smell" a female from as much as a mile away. The chemical similar to the pheromone that the female gives off is now synthetically made and is used in gypsy moth traps. Adults do not feed but will mate and die soon after the eggs are laid.
There are reports of skin rashes and respiratory problems due to airborne gypsy moth body parts such as their wing scales, larval hairs.
There are several controls that are both natural and artificial being tried on gypsy moth. In nature, there are viruses, fungi, bacteria, and predatory wasps. In the home landscape, there are several possible control methods. Trapping is used to help determine the severity of the infestation. Bacillus thuringensis kurstaki can be commercially applied as well as synthetic insecticides to control gypsy moth. But Bacillus thuringensis kurstaki is as effective and is environmentally safe because it occurs naturally in the environment.
Written by James Schuster, Extension Educator, Horticulture, and reviewed by Philip L. Nixon, Extension Specialist-Entomology, Department of Natural Resources and Environmental Sciences University of Illinois at Urbana-Champaign.