52 Bulletin 233. 



and Scotch elms. In this country, Dr. Felt reports it on these trees and on 

 American elms also. On the Cornell campus there is a case where American 

 and Scotch elms grow so near that their branches often mingle, and although 

 the sawflies are often seen on the leaves of both trees, yet not a leaf on the 

 native trees are ' ' blistered ' ' by the insect while the foreign trees are badly 

 infested. In this locality the American elm seems to be almost entirely exempt 

 from the pest. The Camperdown variety of Scotch elms is often infested. 



Work and destructiveness of the insect. — Its work is quite conspicuous, 

 as is shown in Fig. 26. Twenty or more of the larvae often mine in a single 

 elm leaf, and their mines soon coalesce forming a large ' ' blister ' ' often in volv- * 

 ing the whole leaf. Many mines just begun are shown in the leaf in lower 

 left-hand corner of Fig. 26, and larvae can be seen at work in larger mines in 

 the leaf in the right-hand corner of this figure. Oftentimes a mine begun 

 near the midrib of the leaf is confined to the area between two large veins 

 until it gets nearer the outer edge where it extends under the smaller veins or 

 into neighboring mines. The whole interior of the leaf is eaten, leaving only 

 the outer epidermis which soon turns brown. The " blisters " are nearly as 

 conspicuous from the lower as from the upper side of the leaf. The mines of 

 its near relative in alder (Fig. 29), scarcely show from the underside of the leaf 

 possibly because the alder leaf seems thicker than the elm. 



In July, after the larvae leave the "blisters" on the elm leaves, the 

 mined areas bleach out to a dirty whitish color, shrivel and curl. The picture 

 of an infested branch in Fig. 26 was taken at this stage. Unless the leaves 

 are wholly mined out, most of them remain on the tree a considerable time 

 longer, the mines often becoming holes. Infested trees present the worst 

 appearance about July ist, or soon after the larvae disappear. As many of 

 the leaves drop off, as the new growth comes on, and as no other broods of 

 the insect appear, the infested trees begin to recover by the end of July, and 

 by September ist., trees which were badly infested in July often show but 

 little signs of the insect's work to the casual observer. 



I have seen small trees almost defoliated, and thus stunted and rendered 

 unsightly by this sawfly miner, and from one-half to two-thirds of the leaves 

 on several large trees on the Cornell Campus have been badly infested for 

 several years. These large trees present a very ragged and unsightly appear- 

 ance about July ist, but in two months have nearly recovered their beauty. 

 The insect is thus capable of defoliating and checking the growth of young 

 trees, and of rendering large trees unsightly for a time in midsummer. 



Its life history and habits.— In 1869, Healy recorded (The Entomolo- 

 gist, Vol. IV, p. 297) many interesting details of the life of this sawfly, and 

 the European literature contains but few additional notes. 



After July isth, I have not found the insect on the trees again until the 

 next May. In July the larvae which mined the leaves go into the ground beneath 

 the trees for a short distance, an inch or less. There they make small, thin, 



