56 Bulletin 233. 



three unhatched eggs and at least , twenty-five mines just begun in a single 

 large elm leaf (Fig. 26).* I have not found any characters which will readily 

 separate the nearly-grown larva of this elm sawfly from those of the alder saw- 

 fly discussed on page 61. 



On May 27th, 1904, I found on the Scotch elms on the Cornell Campus 

 many of the sawfiies, many recently laid eggs and many larval mines just 

 begun in the leaves. By June ist, some of the larvae were nearly grown and 

 on July 4th, practically all had left the leaves, no stage of the insect being 

 found on the trees. The larvae (Fig. 24) apparently live as miners in the leaves 

 for about, three weeks when they moult for the last time, bite through the roof 

 or floor of their home and drop to the ground. Burrowing in an inch or less, 

 they soon make the thin, brown, papery cocoon in which they remain in hiber- 

 nation as larvae for about ten months, or until the next May. 



There is thus but one brood of this elm sawfly in a year, its destructive 

 period being the month of June, but many of the " blistered " and unsightly 

 leaves remain on the trees as mementoes of its work until autumn, t It is a 

 fortunate provision of Nature that there is but a single brood of this pest in a 

 season, otherwise it would certainly defoliate badly infested elm trees, which 

 now have a chance to largely recuperate and regain their beauty before autumn. 

 The single -brooded habit of this elm sawfly is in striking contrast to the three 



* The following interesting details of tlie larval stages are quoted from Healy's account 

 (The Entomologist, IV, 298). " The larva has a white body, and is in possession of 22 

 legs, the first six of which are annulated with dark brown ; the claws are also dark brown ; 

 the head is tinged with pale brown of a darker tone at the sides, mouth reddish brown, eye- 

 spots brown, and its dorsal vessel is dull green ; the under side of the second segment has 

 a dark, oblong-shaped plate down its centre, and on either side of this there are two brownish 

 dots ; on running our eyes down the remaining segments we observe that, excepting the 

 anal segment, all are furnished with a small black-colored dot ; the fifth segment has no 

 organs of progression. At the first moult the decorative markings of the larva are all 

 thrown off, and if at that time we closely inspect the under surface of the body we perceive 

 a slight remnant or pigmentary deposit on the segments situated as the exact spots where 

 the black ventral dots were located previous to the moult ; these dusky marks, however, 

 soon fade away, and leave the segments entirely spotless ; the head and eyes slowly resume 

 their original color, and the six thoraic legs regain their annulations ; When full-fed it 

 ceases to feed, and lies in its mine in a state of repose, and throws off its skin for the last 

 time i by and by a faint yellowish tinge spreads itself over the body of the larva. At the 

 appointed time the larva liberates itself from its mine by biting a hole in it. At the last 

 moult the brown-colored bands on its six anterior organs of locomotion are thrown off 

 entirely. Escaping from its mined abode, the little creature drops to the ground, and now 

 every time it is touched, it instantly partially curls its body up, remaining in that position 

 only for a moment or two." 



t Healy states (The Entomologist, IV, 298) that in England there is only one brood dur- 

 ing the season, and that by the end of June they are all under ground. Cameron states 

 however, that he has captured the flies in August in England (Mon. British Phpt. Hym. i, 

 p. 296), and intimates that there is probably an autumnal as well as a spring brood, but 

 Cameron's experience must be very exceptional. 



