165 



1993) and from urban plantings and nurseries in many areas of California (New- 

 combc and Chastagner 1993b). The widespread nature of the infestation indicates 

 that the rust has been present along the Pacific coast for years. 



Mdampsora ianci-popuUna rust requires two hosts, a Populus species and a coniferous 

 species, to complete its life cycle. In both hosts, poplar leaf rust can cause severe 

 defoliation that reduces growth and may induce physiological disorders (Newcombc 

 and Chastagner 1993a). 



Other Exotic Pests 



The preceding summaries of infestations represent examples of exotic pests that have 

 caused notable destruction to a particular species or ecosystem. Forest Service staff have 

 compiled lists of all exotic pests, insects, and diseases that have been introduced to North 

 American trees, tree nurseries, and wood products. These lists now total over 300 spe- 

 cies (Millers et aL, unpublished manuscript and personal communication). Some of the 

 pests cause as much damage as die examples presented in this paper, e.g., European 

 spruce sawfly (Gilpinta hercymae). Other pests damage trees in a less obvious manner, re- 

 ducing vigor through feeding/parasitism or providing an environment for a secondary 

 pest to invade the tree. A good example of a pest that probably causes widespread, 

 but not lethal, damage is the Asiatic oak weevil (Cyrtepistomm castaneus). Larvae of 

 this pest overwinter in the ground, feeding upon root hairs of the host planL Adults 

 feed upon the foliage of the host plant after emergence. Ferguson el oL (1992) sus- 

 pected that damage from Asiatic oak weevils may negatively affect oak regeneration. 



New pests are continuously being imported, despite APHIS regulations and quaran- 

 tines. The common (or larger) pine shoot beede (Tomicus (= Blastophagus) pimperdia) 

 was first discovered in July, 1992 infecting Scotch (Scots) pine near Qeveland, Ohio 

 (Kucera 1992). Since the initial discovery, infestations have been found in New York, 

 Pennsylvania, Illinois. Indiana, and Michigan. This pest has attacked a variety of 

 Eurasian and North American pine species. APHIS has quarantined movement of 

 logs, Christmas trees, and nursery stock of coniferous species from the infested states. 



Eleven specimens of another exotic pest, the spruce beetle (Ips typographus) , were 

 captured in pheromone traps near a dunnage pile in the port area of Erie, 

 Pennsylvania in sprmg 1993 (Hofacker 1993). Wliile the Siberian risk assessment 

 states dial this insect normally utilizes dead wood (USDA Forest Service 1991b), 

 Snuth (personal communication) states that "[t|his insect is one of the most destruc- 

 tive pests of spruce in Europe; one outbreak destroyed an estimated 30 million cubic 

 meters of wood. The bceUe also killed millions of trees in Japan." .-VPHIS and the 

 Forest Service have placed numerous additional traps to document the spread of this 

 pest and are searching for potential breeding areas to determine whether the bcetie 

 has become established in the area (Hofacker 1993). 



