158 



formerly known as pests of Cniit trees, have switched host preference to sugar maples 

 and other forest tree species. Dam^e is highly variable by year and geographic loca- 

 tion. For example, Pennsylvania found 100,000 acres of heavy defoliation in 1982, vir- 

 tually none in 1983 and 1984, and 110,000 acres of heavy defoliation in 1985 

 (Laudermilch 1988). 



Control methods have not been developed yeL All pear thrips identified in the U.S. 

 are females and are believed to reproduce by parthenogenesis (Laudermilch 1988). 



Winter Moth 



The winter moth {Operophtera brumata) feeds on various broadleaf trees, including 

 maples, hawthorns, cherry, poplar, oaks, apple, and willow, in the Canadian Maritime 

 provinces and U.S. Pacific Northwest forests. The moth was accidentally introduced 

 into Nova Scoua, probably in the 1930s (Embree and Otvos 1984). By 1952, it had 

 become a serious pest over much of Nova Scoda. Hardwood foresis, particularly those 

 containing northern red oak and wild apple, were severely defoliated. Two exotic par- 

 asites, CyiCTiii albicans and Agrypon JUweolatum, were released from 1955 to 1959, and 

 moth populauons subsequendy collapsed (Embree 1991). Moth populations in nauve 

 forests of the Maritime provinces now appear to be controlled by a combinadon of 

 life history factors and the two introduced parasites (Embree and Otvos 1984; 

 Embree 1991). Sporadic outbreaks are now associated with early-leafing tree and 

 shrub species, with litde infestadon of oak species (Embree 1984). 



The winter moth was first reported in western North America in 1976 (Gillespie et aL 

 1978), but evidence indicates it had been established in Oregon for many years (Kim- 

 berling et al. 1986). It is unknown whether western infesutions were due to a migra- 

 tion from eastern Canada or to a separate introduction from Europe (Kimbcriing et 

 aL 1986). The distribution rate of the insect in Oregon has been slow, imlike the ex- 

 perience in Nova Scotia. The reason may be the lesser abundance of host plants oi. 

 which leaf buds open sufficiently early for the moth to uke best advantage 

 (Kimberling et al. 1986). It is suU too early to determine whether the parasites will be 

 efTecuve in British Columbia and Washington State (Kimberling elaL 1986). 



Winter moth has a broad host range and is adaptable to different temperature regimes. 

 It is widespread in Europe and will probably continue to expand its range in North 

 America. 



Butternut Canker 



Butternut or white walnut (Juglaiu dnera) is a highly valued hardwood species. The 

 tree is closely related to black walnut (Juglans nigra), but can grow on a poorer, drier 

 site. Butternut is harvested for veneer and lumber for furniture and carvings. The 

 hcartwood of butternut is lighter than black walnut and has a beautiful grain. 

 Butternut is a hard mast species, producing nuts that are a component of many 

 wildlife species' diets. The nut is palatable for human consumption, and 21 cultivars 

 have been selected for orchard production (Millikan and Stefan 1989). 



Butternut populations have been infested by the fungus Siracoccus clavigignenti^glan- 

 daaxtrum. that causes multiple branch and stem cankers. Cankers produced on the 

 main stem will eventually girdle the tree and cause death. The disease was first discov- 

 ered in 1967 in southwestern Wisconsin (Renlund 1971), but is believed to have origi- 

 nated lix>m the eastern coast (Anderson and LaMadeleine 1978). Butternut canker 

 has spread throughout much of the species' range. The 1991 Forest Insect and 

 Disease Conditions in the United States survey (USDA Forest Service 1992) reports 



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