Management

First of all, it is important to understand that Gypsy moth in the USA is here to stay. It will not be eradicated from this country. However, there is no need to panic once Gypsy moth has been detected in a given area. The only way to manage Gypsy moths is to arrest their migration. The main strategy to manage Gypsy moth movement is called Slow-The-Spread (STS), which is designed to delay the amount of new territory invaded through trapping and applying insecticides. In order to further prevent the spread, before moving out of an infested area, be sure to visually inspect all vehicles and outdoor items to prevent transporting Gypsy moths to uninfested areas. Movement of Gypsy moth throughout Illinois will depend on geographic distribution of host plants. Artificial barriers such as corn and soybean fields may slow the spread of Gypsy moth.

In order to determine the spread of Gypsy moth federal and state regulatory agencies conduct comprehensive Gypsy moth trapping programs. Delta or milk carton traps, which vary in color from green, orange, or brown are distributed within areas known to have Gypsy moth and at the leading edge of an infestation to track its spread. The traps are baited with a lure, which is a natural pheromone that attracts the male Gypsy moth. This provides a means to determine the potential infestation of an area and if a quarantine should be implemented. Do not disturb or move Gypsy moth traps. Do not put out your own Gypsy moth traps unless your area is generally infested. The capture of male Gypsy moths in traps does not necessarily mean that Gypsy moths have become established. When large numbers of Gypsy moths are detected in traps, then an area may be designated as quarantined.

Climatic factors such as temperature may influence Gypsy moth populations. The severity of cold during the winter can have an impact on the survival of Gypsy moth eggs. A temperature of –20°F is lethal to overwintering eggs. Eggs that are laid higher up on the bark of trees suffer higher mortality than eggs located near the ground. This probably has to do with the amount of soil warmth and snow cover. Snow acts to insulate eggs from cold temperatures.

Proper cultural practices such as watering and fertility will assist trees in overcoming Gypsy moth feeding. Healthy trees are able to produce an abundance of chemicals, such as phenols, in their leaves. When fed upon by caterpillars this can reduce their size and, consequently, the size of the female's egg mass. Incorporating a diversity of new plantings, especially plants less susceptible to Gypsy moth, into landscapes, parks, and recreational areas may minimize the impact of Gypsy moths.

Egg removal may greatly reduce the number of caterpillars. Remove egg masses by scraping them off trees or other objects and dropping them into a solution of soapy water. A hard spray of water can be used to knock eggs off of trees. Wrapping burlap near the base of trees will trap females as they look for a place to lay eggs.

For recommendations on managing Gypsy moth with insecticides consult the current Commercial Landscape and Turfgrass Pest Management Handbook (for commercial use), the current Home, Yard and Garden Pest Guide (for homeowner use), or contact your local University of Illinois Extension office. Treating localized infestations with an insecticide will slow the spread. However, this only temporarily reduces the number of caterpillars. Pest control materials are best applied when the caterpillars are small. This enhances the effectiveness of these materials, as they are less effective as caterpillars increase in size. One of the commonly used pest control materials for managing Gypsy moth is the bacterium, Bacillus thuringiensis 'Kurstaki' (BtK). BtK must be consumed in order to kill Gypsy moth larvae. The best time to spray with Bt is just after egg hatch when bridal wreath spirea (Spiraea x vanhouttei) is in bloom. The young caterpillars are much more susceptible to Bt than older, larger caterpillars. BtK is not harmful to beneficial organisms such as honeybees.

Gypsy moth is susceptible to attack by various natural enemies such as parasitic wasps (parasitoids), predators, and pathogens (fungi and viruses). The major parasitic wasps are the egg parasitoid, Ooencyrtus kuvanae and a parasitic fly of the caterpillar, Blepharipa pratensis. A large predatory beetle, Calosoma sycophanta feeds on Gypsy moth caterpillars. A fungus, Entomophaga maimaiga, which has been found in Illinois, causes a disease in Gypsy moth larva that kills them. It was introduced into the USA in 1909. However, it was undetected for over 80 years until it was recovered again in the late 1980's. This fungus overwinters as a resting spore within dead caterpillars. It infects live caterpillars in the spring. The abundance of the fungus depends on wet weather because the fungus performs best under moist conditions. The spores (conidia) are spread by wind and infect other caterpillars. The fungus can kill caterpillars within one week. E. maimaiga will infect Gypsy moths at low populations. It is possible that this fungus, which is found in the soil, may follow the spread of Gypsy moth.

During outbreaks or when populations are high, Gypsy moths may be killed by a viral organism known as nucleopolyhedrosis virus (NPV). Unlike E. maimaiga, the virus only occurs under outbreak conditions, because caterpillars are generally crowded and stressed from lack of food.

In addition, vertebrate animals such as mice or shrews will feed on Gypsy moth caterpillars. However, just like many of the natural enemies of Gypsy moth, they don't kill enough Gypsy moth caterpillars to prevent or minimize defoliation of trees.

Adapted from Entomology Fact Sheet, NHE-153 written by Raymond A. Cloyd and Philip L. Nixon, Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, Illinois, in cooperation with the Illinois Natural History Survey.