10 



ILLINOIS NATURAL HISTORY SURVEY 



CIRCULAR 53 



rier of the fungus, feeds mainly in crotches of 1- and 2-year-old twigs 

 (Fig. 8). The fungus spores (Fig. 9), deposited in the feeding wounds 

 (Fig. 10), grow and spread in the vessels of the young sapwood. In- 

 fection occurs mainly in May and early June, when the springwood 

 vessels are adjacent to or near the inner surface of the bark. In time 

 the leaves on branches invaded by the fungus wilt and the branches 

 die. 



In Illinois there are two broods of the smaller European elm 

 bark beetle each year. The first brood of adult beetles (which have 

 overwintered as larvae in elm bark) starts emerging in May and con- 

 tinues to emerge until mid-July. Emerging beetles make small holes 

 in the bark (Fig. 11). Peak emergence of this brood occurs in mid- 

 June. The second brood, which develops in 5-7 weeks from eggs laid 



Fig. 7. — Adult of the smaller Eu- 

 ropean elm bark beetle. It is shiny, 

 dark reddish brown, and about one- 

 eighth inch long. 



^:^f^:. 





Fig. 8. — Close-up of a 

 bark beetle feeding in the 

 crotch of a young shoot. 

 Spores of the Dutch elm 

 disease fungus adhere to 

 the body of this beetle. 



