152 



American elm clones have been identified with good resistance to O. ulmi, and a 

 number of hybrid elms and Asian selections have been released for urban plantings. 

 Evaluadons of resistant American elms in forest setdngs have not yet been conducted. 



Gypsy Moth 



The European gypsy moth has the broadest host range of all exodc pests in Norti. 

 America. The larval stage (caterpillar) defoliates a wide variety of woody plants, 

 although it prefers hardwood trees. Oak species, which have dominated upland for- 

 ests since the chestnut blight epidemic, are a preferred food source. Understory spe- 

 cies important for mast production, tg., hazelnut, serviceberry, and hawthorn, are 

 also favored food of gypsy moth larvae (cf. Gottschalk 1993). When preferred food 

 sources are not available, older larvae feed on a variety of other woody plants including 

 coniferous species of pine and spruce, arbor-viue, and hemlock. 



The insect was deliberately imported in 1869 to the U.S. in an attempt to esublish a 

 domesuc silk industry. Gypsy moth was first observed as a forest pest in Massachusetts 

 within 10 years of the original importadon date. The pest has slowly spread through- 

 out the northeastern states in subsequent years. By 1991, gypsy moth had infested 

 200,000 square miles of the Northeast, with addidonal outbreaks in North Carolina, 

 Tennessee, Arkansas, Ohio, Michigan, and Wisconsin. Infestations of gypsy moth 

 have also been reported in Washington, Oregon, California, and British Columbia, as 

 well as in the Rocky Mountain states. 



Gypsy moth infestations are cyclical. In 1978, 643,600 acres were defoliated, but in 

 1981, defoliation affected 12.9 million acres. An estimated 125 million acres were 

 infested nauonwide in 1991. of which 4.1 million acres (3 percent) were defoliated 

 (Burkman et aL 1993). On the advancing front, the moth is perpetually at high popu- 

 lation levels (USDA Forest Service 1991b). 



Defoliation induces trees to drain energy reserves in attempting to refoliate. A healthy 

 tree can usually withstand several consecutive defoliations of greater than 50 percent. 

 Extensive feeding by gypsy moth larvae affects umber and recreational industries and 

 alters the complexion of existing ecosystems. Mortality from defoliation can be as 

 high as 90 percent where gypsy moth populations are at an epidemic level (Herrick 

 and Gansner 1987). Although defoliation may not always result in tree morulity, 

 diameter and volume growth will decline (Baker 1941, Twery 1987) and wood quality 

 can be affected (Twery 1990). 



Gypsy moth defoliation will alter the species composition of the flora and fauna in a 

 forest ecosystem by causing more nutritional resources to reach the remaining trees 

 and plants in the over- and understory (Allen and Bowersox 1989). A change in the 

 composition of plant species often affects certain wildlife populations and ultimately 

 wildlife food chains. Water yield and quality in forest rivers, streams, ponds and lakes 

 can be affected by gypsy moth activities. Water yield within a watershed increases after 

 defoliation (Corbett and Lynch 1987). The decomposition of additional detritus on 

 the forest floor increases the amount of nitrogen and other nutrients entering a 

 water system and can alter water quality (Swank et al. 1981). 



Gypsy moth infestations have an adverse influence on recreational use and associated 

 industries. Alterations in plant and animal populations and water quality will have an 

 influence on forest use for hunting and fishing. Heavy defoliation will reduce the aes- 

 thetic quality of the forest as a whole (Hollenhorst et aL 1993) and can result in a 20 

 percent reduction in recreational use in the infested area (Goebl 1987). 



