Two New Shade-Tree Pests. 129 



of the insect being foimd on tlie trees. The larvEe (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 hibernation as larv?e for about 

 ten months, or until the next May. 



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

 tive period being the month of June, but many of the " blistered " and un- 

 sightly leaves remain on the trees as mementoes of its work until 

 autumn.* 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 recviperate 

 and regain their beauty before autumn. The single-brooded habit of this 

 elm sawfly is in striking contrast to the three or more broods of its very 

 near relative, the alder sawfly miner, discussed on page 134, which con- 

 tinues to work on the alder leaves from May vmtil October. 



Remedial suggestions. — The suggestions given on page 135 for con- 

 trolling the closely allied alder sawfly will also apply to this elm sawfly 

 miner. 



Last autumn a treatment that doubtless materially reduced the num- 

 bers of these sawflies was unwittingly applied to some of the worst in- 

 fested elm trees on the Cornell Campus. In grading, several inches of 

 new soil was spread over the ground beneath the infested trees. Appar- 

 ently many of the little sawflies failed to emerge through this layer of 

 soil in the spring. As practically all of the sawflies transform within an 

 inch of the surface immediately beneath the infested trees, it would be 

 practicable in some cases to apply a layer of soil several inches thick 

 under the trees in autumn and remove it about June ist, or after the 

 time for emergence of the sawflies. Whenever practicable, however, I 

 would advise the removal or spading under and packing down of the 

 sod from beneath the trees as described on page 135, for I think this 

 method is more effectual. 



Last spring other peculiar conditions occurred in the clump of badly 

 infested European elms on the University Campus, 'it was the fruiting 

 season for several of the trees and they bloomed and fruited profusely. 

 This process delayed the appearance of the leaves until after most of the 



*Healy states (Tlie Entomologist, IV, 298) that in England there is onl}- one 

 brood during 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 Phyt. Hym., Vol. 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. 



9 



