1914] Pemphigine Attacking Populus In Colorado. 67 
Mordwilkoja vagabunda Walsh.,* Plate I, Figures 15 to 20. 
Byrsocrypta vagabunda Walsh, Proc. Ent. Soc. Pha., V. I, p. 306, 1862. 
Pemphigus vagabundus, Walsh and Riley, Am. Ent. V. I, pp. 57 and 107, 1869; 
Riley, V. I, Mo. Rep. p. 120, 1869; Packard, Guide to Study of Insects, p. 524, 
2nd. Ed. 1870; Thomas, Ent. Rep. Ill., V. I, p. 153, 1880; Oestlund, Aphids Minn. 
p. 22, 1887; Packard, Forest Insects, p. 434, 1890; Osborn, Cat. Hemip. Ia. p. 130, 
1892; Cowen, Bull. 31, Colo. Exp..Sta. p. 116, 1895; Hunter, Aphid. of N. A., p. 
79, 1901; Cook, O. Nat. V. IV, p. 118, 1904. 
Pemphigus oestlundi n. sp., Cockerell, Ent. News, p. 34, 1906. 
Pemphigus vagabundus, Jackson, Genus Pemphigus, Cols. Hort. Soc. XXII, 
p. 200, 1908. 
Mordwilkoja oestlundi, Davis, William’s Aphidide of Neb. p. 4, 1911; Patch, 
Bull. 213, Me. Exp. Sta. p. 100, 1913. 
The galls of this louse at the terminal buds of cotton- 
wood twigs have occurred in greater or less abundance in at 
least one limited locality near Fort Collins, Colorado, for 
the past fifteen or more years. The section referred to is 
mostly rather low, moist land, along the course of an irrigating 
ditch and near the river. It seems strange that the galls 
should not have become more generally distributed unless the 
alternate host is largely limited to the area mentioned. I am 
assuming that there is an alternate host for the reason that 
the lice all become winged and leave the galls rather early in 
the summer. Most of them are gone by August Ist here. 
The Galls, Figures 18, 19 and 20. 
When growing, the galls are as green in color as the cottonwood 
leaves, and are, in fact, a transformed leaf in each case. On the inside 
of the green gall the main veins of the leaf are very prominent. 
Apparently these galls differ from others produced by Aphids by not hav- 
ing any opening to the exterior during their growth, but Mr. L. C. Bragg 
has discovered a small brown scale (Figure 18 A, and 20, b) at the base 
of the gall, which seems to be the apex of a folded leaf, beneath which 
is an opening to the interior and through which the blade of a pen- 
knife may be passed without cutting any tissue. This opening is so 
narrow that the lice do not escape by it. About the time that fully 
matured winged lice are developed in a gall (about July 10th to 15th, 
*Professor Oestlund, in his Aphidide of Minnesota, p. 22, states that Walsh's 
vagabundus is evidently something different from the louse that has since been 
known to be associated with the coxcomb gall. To be sure, September is late 
to take the migrants from these galls, and the measurements given by Walsh are 
too large for this species. But he evidently had a louse belonging to the Genus 
Pemphigus, as then understood, and in the Walsh-Riley paper published in Vol. 
I, of American Etomologist, page 107, the vagabond gall was figured, and both the 
winged lice and the apterous stem mothers from the galls mentioned. As Walsh 
at that time considered the winged lice from these galls the same as what he had 
described as B. vagabunda, it seems to me best to abide by his identification of 
his own species, and especially as we do not know any other species to which 
to refer his original description, which is quite inadequate for its identification 
anyway. I am therefore retaining the name vagabunda. 
