SYNOPTICAL KEY TO THE APHIDIDAE OF MINNESOTA 123 
as long as the body, and the spur of the terminal segment longer than. 
the basal part; cornicles short and truncate, not longer than wide, 
cauda short and broad, triangular or globate, projecting beyond the 
rounded anal plate. The following genera are represented in Min- 
nesota: 
a. Cauda short and broad, like the Pterocommini; veins with dusky borders ; 
found- on Populus. ...c.cccceseceieses Genus NEOTHOMASIA 26 
b. Cauda triangular; with dimorphic summer forms; found on maple and 
OE CLL CT Pear etches lek ers teal ae Rants EES Genus -RPERIPRYLEUS 27 
c. Cauda triangular or globate; no peculiar summer generations present; 
found on willow end poplar......... Genus CHAITOPHORUS 28 
26. Genus NEOTHOMASIA (Wilson) Baker, 1920. Type: 
Chaitophorus populicola Thomas, 1879. Cauda broad; habitat Populus. 
The generic characters approach the Pterocommini and represent the 
generalized and transitional forms of the Chaitophorini. Only one 
species is recorded and rather common in the state: 
(16) NEOTHOMASIA POPULICOLA (Thomas) Baker, 1920 
Common on cottonwood. 
27. Genus PERIPHYLLUS (Thornton) Van der Hoven, 1863. 
Type: Phyllophorus testudinatus Thornton, 1852. The genus is well 
characterized by the presence of summer generations that are very 
different from the ordinary spring and fall forms; the dimorphs are 
very small and greatly depressed, with fanlike setae around the margin 
of the body, and show no disposition to grow or change for a month 
or more. The habitat of the genus is maple and box elder. 
(17) PERIPHYLLUS NEGUNDINIS (Thomas) Baker, 1920 
Rather common and sometimes injurious to box elder. 
28. Genus CHAITOPHORUS Koch, 1854. Type: Aphis popula 
Linnaeus, 1758. Cauda usually enlarged at apex or globate. The 
dimorphic summer forms are never present. The habitat of the 
genus is willow, poplar, and oak. Several species are known from 
the state, but the species are difficult to separate and have not been 
sufficiently studied: 
me) CHAITOPHORUS VIMINALIS Monell, 1879 
Surface of the head with broken reticulations or granulations; 
spur long; color yellowish green. 
(19) CHAITOPHORUS NIGRAE Oestlund, 1886 
Surface of the head with distinct reticulations, not broken; colors 
green or black. 
