134- Bulletin 233. 



The life-history and habits of the insect. — As late as October a 

 few of the larvae were making their characteristic mines and brown 

 " blisters '" on the leaves of the trees on the Cornell Campus. The winter 

 is passed as larvae tucked away in their little, brown, elliptical, papery 

 cocoons mostly about half an inch below the surface of the soil beneath 

 the infested trees. In ISlay these hibernated larvae transform, in about a 

 week, through tender, pale yellowish pupae with brownish-black eyes into 

 the shining black adult insects or sawflies. The adults usually begin to 

 emerge by May 15th, and begin laying eggs at once. On June 8th in 1904, 

 I found many of them busy laying eggs in the younger leaves, and a few 

 larvae had already nearly completed their mines. I have never seen the 

 flies mating, and have found no males. Thus the insect seems to breed 

 parthenogenetically. A small, thrifty tree which w^as putting out much 

 new growth in 1904, was severely attacked in June while older trees 

 nearby suffered but little, until about a month later. 



The egg is about .3 mm. in diameter, round, thin-shelled and of a 

 delicate milky-white appearance. The female sawfly saws a slit in the 

 leaf from the upper surface and tucks her egg in just under the upper 

 epidermis of the leaf. Most of the eggs are laid in the central portion of 

 the younger leaves between the larger veins. It requires about a minute 

 to lay an egg. Over the egg the surface of the leaf is slightly elevated 

 and turns yellowish, thus enabling one to easily locate the egg (Fig. 28) ; 

 this is more distinctly seen from the upper surface of the leaf. Evidently 

 the eggs hatch in a few days and the little larvae begin their life as 

 miners. 



The greenish-white, slightly flattened, distinctly segmented larvae with 

 light brownish heads and short apparently useless legs are shown much 

 enlarged in Fig. 24. The duration of the larval period I have not de- 

 termined, but it is probably about three weeks.* One larva mines over 

 an elongate area, about the size of a one cent coin, which is often bounded 

 by two large veins for some distance before it merges into a neighbor's 

 mine (Fig. 29). Frequently the rusty brown "blisters " or mines of ten 

 to twenty larvae coalesce and involve nearly the whole leaf, which soon 



* Dyar has described in detail six larval stages (Can. Ent., XXV, 247). In the 

 fifth or last feeding stage, the larva is translucent whitish with a greenish tinge 

 from the food, and it measures 6 to 7 mm. The head is much flattened and of a 

 light brown color with the mandibles and ocelli darker. The true legs, tlie ventral 

 surface of the first thoracic segment, small spots on the venter of the other thoracic 

 segments, and the cervical shield are brownish. The abdominal legs are rudimentary 

 and present on joints 5 to 12. No tubercles or seta; are distinguishable. I have 

 found no striking differences between these larvre and those of the European elm 

 sawfly leaf-miner, Kaliosys(>hinga dohniii, therefore Fig. 24 may represent both 

 speciQ§, 



