SUBFAMILY ERIOSOMATINAE 373 
Genotype Forda formicaria Heyden 
The Grain Root Aphid 
Forda formicaria Heyden, 1837:292; Theobald, 1929:169 and 350; Gillette, 1918c:282. 
Forda occidentalis Hart, 1894:95; Mordvilko, 1928:1070; Gillette and Palmer, 1934: 
237; Mordvilko, 1935:145 (synonym—Pemphigus semilunarius Passerini, 1856). 
Apterous Summer Vivipara. Pale to medium olive-green or grayish green, mottled; head 
and appendages pale brownish. Body length 2.6-2.8; hind tibia .80-.85; antenna .80-1.1; ros- 
trum attaining mid-abdomen. Hairs simple, .05.0on vertex and III and side of abdomen. 
Alate Summer Vivipara. Head and thorax black; abdomen sordid straw-yellow to olive- 
green; with dusky dorsal bands and lateral areas; appendages blackish; veins of fore wing 
heavy and slightly bordered. Body length 2.2-3; antenna .80-1; hind tibia .80-1.20; rostrum 
attaining abdominal I. 
7 & oo 
(35-50) WIZ —.2/) (11 = 18)+.03 
-55) 
Fig. 450. Forda formicaria 
Collections. Primary host, Pistacia terebinthus, according to Mordvilko 
(1935:145) (not occurring naturally in North America); secondary hosts, Melica 
bulbosa, Poa pratensis, Phleum alpinum, Elymus sp., on roots and in ants’ 
nests. Colorado: Longmont, Estes Park, Masonville and Fort Collins. Apterous 
viviparae all the year around; alate viviparae June 2 to July 2; common. 
Our species as described by Gillette (op. cit.) has been declared distinct 
from F. formicaria by Theobald (1929:174) on account of supposed differences 
in length and sensoriation of antennal segments in alate vivipara. Theobald 
was possibly misled by statement by Gillette that number of sensoria on III 
were 30. This appears to be the smallest number occurring in the specimens so 
far examined, the variation being from 30-55. This abolishes the difference 
maintained by Theobald. An alate and an apterous vivipezrous specimen deter- 
mined as F. formicaria by Hille Ris Lambers, appears identical with our form. 
Furthermore, comparison of our form with cotypes of F. occidentalis Hart 
(op. cit.) revealed no differences except such as were attributable to imma- 
turity of Hart’s examples. These facts appear to confirm Gillette’s opinion (op. 
cit.) that the Colorado form is F. formicaria Heyden and that F. occidentalis is 
a synonym. 
Forda olivacea Rohwer 
Forda olivacea Rohwer, 1908:68; Gillette, 1918c:283; Gillette and Palmer, 1934:238; 
Mordvilko, 1935:164 (=wilsoni Mordvilko). 
Apterous Vivipara. Sordid greenish yellow, dusky on head and somewhat on pronotum, 
and on dorsal bands on abdominal VII and VIII and cauda; appendages sordid yellow to 
slightly dusky. Body 2.5 by 1.5; hind tibia .45; hind tarsal II .15; antenna .54; rostrum at- 
taining 3d coxa. Dorsum of head and body thickly covered with spinules. Hairs inconspicuous 
or not evident, not longer than .01, sparse. 
Alate Vivipara. Head and thorax black; abdomen dark olive-green, with dusky dorsal 
bands on all segments; appendages black. Body length 1.8-2.5; hind tibia .75-.80; antenna 
.65-.70, rostrum attaining 2d coxa. Hairs not evident on vertex; on antennal III, hind tibia 
and on side of abdomen .01. 
