Pachypsylla celtidis-mamma Riley. Host CelHs occidentalis L. A complicated form of pouch-gall produced in the mesophyll of the leaf of the host. On the upper surface of the leaf the gall is indicated by a decided depression in the centre of which is a slight elevation that marks the opening of the gall. The part projecting from the lower surface, is oblate-spheroidal in shape, attached to the leaf by a slightly tapering cylindrical stalk. The average number of galls found on a leaf is usually about ten, but in some cases much higher. The surface of the gall is smooth except for a few fine scattered hairs, glaucous and greenish- yellow in colour. Dimensions: — Height from point of attachment 6-7 mm.; width 7-8 mm. The anatomical structure of this gall shows it to be a more complex type than any other of the Hemiptera discussed in this paper. Besides the folding of the leaf the blade has been further changed in thickness and in the character of the cells. The production of the greater part of the abnormal tissue is due to a wide, well differentiated cambium layer, that extends right across the gall and at its margin passes into the tissues of the normal leaf between the palisade and the spongy parenchyma (Fig. 15). The larval chamber is lined by this cambium sheath which thus functions as a nutritive layer. Bordering this zone is a well developed protective tissue composed of cells with uniformly thickened walls. The sclerenchyma is laminated and pene- trated by branched canals, presenting the same character as that found in the galls of the Cynipidae. Outside of this protective zone lies the chief mass of the gall, com- posed of thin-walled irregularly shaped cells, as illustrated in Fig. 15. Typical cells of the protective sheath are also found scattered throughout this tissue. As the gall becomes older these cells increase in number.

Pachypsylla rohweri n. sp.

Galls crowded on underside of leaf of Celtis reticulata Torrey; about 6 mm. diameter, elevated, mammiform, with a long nipple-like protuberance. Mr. S. A. Rohwer collected the galls at Boulder, Colorado (where I have also found them), and bred the adults August 30, 1907.

Pachypsylla celtidismamma (Riley) (occidentalis nipple gallmaker)

Gall. This gall is much larger than those of the other nipple galls. On the upper leaf surface they are seen as cup-shaped depressions 4 to 5 mm in diameter, in the central part of the cup there is either a short projection or a distinct spine. Below the gall projects usually as a vertical cylinder for 5 to 7 mm, the end may be truncated or somewhat irregularly pointed. Texture rugose reticulate. Color greenish yellow at maturity, not shining.

Hosts and distribution: In view of the numerous forms with which this species has been confused the distribution records for it are somewhat unreliable, but probably it occurs throughout the range of its known host C. occidentalis. I have seen specimens which could be readily determined as P. celtidismamma from Texas, Oklahoma, Kansas, New York and Delta, Manitoba, and rather definite records are available for it from Ohio and several other midwestern states. The Texas specimens were collected near the Panhandle towns of Canadian, Miami and Wheeler.

P. celtidispubescens and P. celtldismamma are sympatric in northwestern Oklahoma and adjacent areas of Texas where they often occur on the same trees.

Pachypsylla celtidismamma (Fletcher, 1883)

Type locality: USA, Iowa.
Additional distribution: USA, widely distributed in eastern and central North America; considered introduced in
California.
Host plant: Celtis occidentalis, C. laevigata.
Remarks: First recorded in California in 1989 (Gill 1989)

Pachypsylla celtidismamma

Celtis occidentalis

Hairy nipple galls. Galls pubescent on the apical portion of the under side, but hairs easily rubbed off, giving glabrous appearance; upper side a depression with central spine but no outer rim; under side nipple-like, longer than wide, without obvious central depression

Widely distributed in eastern North America, north to Ontario, south to NC, east to CT, NY, west to NE, KS, OK

Pachypsylla rohweri

Celtis reticulata

Hairy nipple galls

CO, TX, OK

Conclusions about the status of several additional described nipple gall makers, including P. celtidispubescens, P. rohweri, P. celtidisglobulus, P. celtidiscucurbita and P. celtidiscucurbita var."?", can not be made, since they were not included in this study.

Pachypsylla mamma (Fig 6)

nearly cylindrical, apex rounded bluntly

Pachypsylla celtidis-mamma

This gall, on upper side of leaf, is represented by a very regular cup-shaped impression, measuring on the average 4.5mm across, with the upper, outer rim always regularly circular, and not, or but slightly, elevated above the surface of the leaf; at the bottom of the cup a small median nipple (often obsolete); walls of the impression greenish, the bottom more yellowish. On the under side of the leaf it is much larger than in any of the other leaf galls, conical, either slightly narrowing apically or, more frequently, slightly enlarged. The sides are vertical or nearly so; the top broadly rounded without median depression or central nipple. Size very variable; averaging in height 6 to 7 mm, and in diameter at base 4 to 5 mm. Color pale greenish yellow, with the tip more brownish; surface opaque, rugosely reticulate; at base often covered with a whitish pruinescence, rarely with a few scattered hairs near the top. The walls of the gall are hard and woody, at the bottom averaging 1.75 mm, at the roof 0.75 mm in thickness. The cell is large, and in cross-section much more crescent-shaped than in the preceding species. The mature pupa issues through an oval slit sawed through the roof, always near the side where the wall is less thick.