INSECTS AFFECTING PARK AND WOODLAND TREES 



637 



oil S. discolor. A smooth, fleshy, sessile, globular, or slightly oval 

 monothaiamous gall, like a miniature apple, .3 to. 55 inch diameter, growing 

 on one side of the midrib of a leaf, and extending to its edge or beyond it. 

 The principal part of the gall projects from the underside of the leaf ; very 

 rarely it is bisected by the leaf. Color greenish yellow, sometimes with a 

 rosy cheek, especially the upper surface and often with little dots. Fully 

 mature July 31. An analogous gall is formed in Europe on various willows 

 by Nematus gallicola Westw. 



The transformations to the yellowish red adult occur within the gall in 



case of specimens reared by Walsh. There was no earth in the jar and 



some cocoons were spun between the galls. 



Pontania pisum Walsh. 



Subspherical, pealike, pale yellowish galls growing on the underside of the leaves of 

 Salix discolor are the work of this species. 



This gall-making sawfly is a common species in some sections at least, 

 and on breaking open the hollow galls a whitish, 18-footed caterpillar with 

 a slightly dusky head and dusky mouth parts may be found within. 



The gall has been described by Walsh as follows : 



A subspherical, pealike, hollow, pale yellowish green gall, always 

 growing on the underside of the leaf and almost always from one of the 

 side veins (in one case from the midrib) and attached to the leaf by only 

 a minute portion of its surface ; .18 to .28 inch in diameter, and a few, 

 immature, only .08 inch in diameter. Almost invariably there is but one 

 gall to the leaf, but on four leaves there were two, and occasionally two 

 are confluent. Surface in some smooth and even, without pubescence ; in 

 others a little shriveled, generally studded in the medium sized ones 

 with four to 12 small, robustly conical nipples, which in the larger ones 

 have burst into a scabrous brown scar. Only in 3 out of 62 was there any 

 rosy cheek, as in S. p o m u m. The point of attachment is marked on the 

 upper side of the leaf by a brown subhemispherical depression. 



The final transformations to the black yellowish marked adult occur 



in the ground. 



