THE COMMON ELM-BORER. 225 



More recently the ravages of this borer have been observed by Pro- 

 fessor Forbes, whose notes we copy from his third report on the injuri- 

 ous insects of Illinois. 



For several years past my attention has been attracted by the gradual decay and 

 death of the rows of white elms ( Ulmus americana) in the towns of Normal, Bloom- 

 Ington, and Champaign. The difficulty with the trees commonly commences to de- 

 clare itself from the middle of summer to autumn, when the leaves, tirst upon the 

 terminal twigs and then upon the larger branches, are seen to stop their growth, 

 change their color, and ultimately to fall. This loss is naturally followed speedily 

 by the death of the branches themselves, as is clearly evident the following spring, 

 when these remain black and lifeless while the rest of the tree is putting on its fol- 

 iage. Usually the higher branches of the tree are those first affected, but the whole 

 top soon seems to blight, and in a year or two the tree perishes utterly. This diffi- 

 culty, commencing here and there, extends slowly from tree to tree along the rows, 

 finally inevitably destroying every tree of this species in the immediate vicinity. 



In autumn of 1883, I directed an assistant, Mr. Webster, to dig up a tree which had 

 nearly died in this manner during the summer, and to carefully examine the larger 

 roots, the trunk, and all the branches, with a view to ascertaining, if practicable, 

 the cause of the difficulty. The roots were found unaffected, but on peeling the bark 

 from the trunk, about half-grown larvae of Saperda tridentata appeared in consider- 

 able numbers in the still living parts of the wood, and those of Magdalis armicollia 

 were abundant where the bark and wood were already dead. The manner in which 

 the bark had been mined and burrowed by the Saperdas gave sufficient evidence of 

 the cause of the death of the tree, the borers having again and again completely 

 girdled the trunk. 



Both the trunk and branches of this tree were cut up in lengths and boxed for the 

 purpose of determining the details of the life history of the species. The specimens 

 were boxed August b, the cracks of the boxes being closed by pasting over them strips 

 of paper, and each having left a glass-covered opening in the top, to which it was 

 assumed that the insects emerging would be attracted. Later, this cover was re- 

 moved, and a glass jar was inverted over the opening. 



Nothing emerged until the following spring, except a single parasite taken Septem- 

 ber 14. On the 9th of April, living larviB of Saperda were found still within the 

 wood, but no imagos had appeared in the boxes, neither were any pupse discovered. 

 On the 17th of that month, both larvie and pupse were detected, and on the 2d of 

 May the first imagos appeared, three in number. On the 3d another imago emerged, 

 on the 5th five more, and on the 7th eighteen, on the 8th eleven, and on the 12th 

 twenty-three, this being the largest number taken from the boxes at once. Beetles 

 continued, however, to emerge at frequent intervals until the 22d of June, at which 

 time the last appeared, one hundred and eighteen in all having been taken alive. 

 On the 15th of September the boxes were opened finally, thoroughly searched, and 

 fifty-three more dead Saperdas wei'e found. The boxes in which these specimens 

 transformed had been kept under cover, but at the natural temperature of the air. 



Although the elm borer has evidently been for several years both numerous and in- 

 creasing in the neighborhood where this tree was destroyed, the amount of parasitism 

 developed by the experiments was quite insignificant, only eight parasitic insects, 

 belonging to three species, appearing in the boxes as against the one hundred and 

 seventy-one examples of the adult borer ; and indeed, as the same pieces of wood con- 

 tained a great host of the larvte of Magdalis armicollis, from which multitudes of 

 imagos of this species emerged during this spring, it is impossible to say that some or 

 most of this small number of parasites may not have escaped from the latter species. 



From the present appearance of the elms throughout the towns of Central Illinois 



where I have had an opportunity to examine their condition, and from the rapid 



progress which this pest has made among them during the last two or three years, it 



seems extremely likely that it will totally exterminate the trees unless it be promptly 



5 ENT 15 



