DUTCH ELM DISEASE IN ILLINOIS 



Fig. 6. — Galleries in which the smaller European elm bark beetles lay eggs 

 are parallel to the grain of the bark and wood; they are few and relatively large. 

 Galleries made by the larvae or grubs of this bark beetle are perpendicular to the 

 grain of bark and wood; they are numerous and relatively small. When the bark 

 is removed, the white larvae are conspicuous at the tips of many of these galleries. 



HOW THE DISEASE SPREADS 



The Dutch elm disease fungus is transmitted to healthy elms in 

 two ways: (1) by insects, (2) through roots that become grafted to- 

 gether between diseased and healthy trees. 



Insect Carriers 



The insects that transmit the Dutch elm disease fungus in the 

 United States are the smaller European elm bark beetle, Scolyhis 

 multistriatus (Marsham), and the native elm bark beetle, Hylurgopi- 

 nus rufipes (Eichhoff). 



The smaller European elm bark beetle (Fig. 7), principal car- 



