July 9, 1917 Study of Eriosoma pyricola 69 



rest of the body and the segmentation is well marked. The beak reaches 

 about to the third abdominal segment. 



This form settles on the underside of an elm leaf near the midrib and 

 generally not far from the base. After the young aphid has fed for a 

 very few days, the leaf begins to curl around it and the curling and 

 twisting become more pronounced as the insect grows, so that by the 

 time it has reached the third instar the leaf in the form of a gall has com- 

 pletely closed around it. This gall is a part of the leaf tissue, ribs, and 

 parenchyma, which has developed independently of the remainder, 

 owing to the puncture and feeding of the insect. The walls of the gall 

 are thicker than the normal tissue, and frequently the petiole is abnor- 

 mally thickened. Galls harboring immature stem mothers have the 

 form of a compact spiral twist. On the outside they bear a thick fringe 

 of whitish pile, and in color they vary from the normal leaf color to a 

 pale yellowish white, often rosy tinted when exposed to much direct 

 sunlight. Many occur which harbor more than one fundatrix, but even 

 those with single tenants vary noticeably in size. The average diameter 

 of galls containing third-instar fundatrices was X inch. 



The young stem mothers in the first instar are greenish gray with 

 grayish "meal" on dorsum and pleura; they are elongate oval. In suc- 

 ceeding instars the color is slaty blue, and considerable fine whitish 

 "wool" issues from pores; the shape becomes short pyriform, and globules 

 of viscous honeydew are ejected from the anus. 



The mature fundatrix is dark bluish green, robust, clothed with white 

 wooly and waxy filaments, the larger of which arise from four longi- 

 tudinal dorsal and dorso-lateral rows of pores; the antennae and legs are 

 yellowish brown; the tarsi, knees, and two distal antennal segments are 

 dusky gray; the beak is very short, yellowish brown, with a gray tip; the 

 dorsum of the head is gray; the eyes are black, simple, and very small; 

 the body is globular oval, becoming greatly distended with age. Re- 

 cently matured stem mothers were collected between May 17 and 23, 

 and it was observed that several matured between these dates. Field 

 observations indicate that this was the period in which the majority 

 reached the adult stage. It appeared that the stem mothers fed from 

 four to five weeks in the immature stages. The galls containing the 

 mature fundatrices varied in diameter from X to X inch, and their 

 shape was a rather short subglobular spiral. Figures A and D of Plate 10 

 show a gall, collected on May 13, which harbored a fourth-instar fund- 

 atrix. 



Following upon the maturing of the stem mother the galls grow very 

 rapidly and change their shape to the form depicted in Plate 10, B, C. 

 The photographs from which these illustrations were made were taken 

 on July 12 and present two diametrically opposite views of the same 

 gall, which contained several hundred inmates. It should be observed 

 that the gall is no longer closed. 



