The frontal margin and the shape of caudal setae (unequal) enable U.
tlaxcalense due to the shape of the frontal margin and the length and ornamentation of SIPH (see the descriptions).
The species of Uroleucon have a frontal margin and a frontal medial tubercle varying in shape; the following terms are used to describe the frontal margin: (1) V-shaped if it is deep with a small frontal medial tubercle that does not alter the profile of the frons; (2) subrectangular, if it is well-defined though not very deep and the frontal medial tubercle is low; and (3) sinuate, if the frontal margin is not very deep and the frontal medial tubercle is almost as high as the frontal lateral ones delimiting the margin.
Head light brown, more or less pigmented like coxae and trochanters; frontal margin V-shaped; dorsal setae 45-68 [micro]m, 1.
Head dark brown, like coxae, and darker than trochanters; frontal margin subrectangular; dorsal setae 58-70 [micro]m, 1.
Head brown to dark brown, near black in more pigmented specimens, darker than trochanters; frontal margin V shaped; dorsal setae 30-65(70) [micro]m, 1.
Head brown, darker than trochanters; frontal margin subrectangular; dorsal setae 45-55(58) [micro]m, 1.
Head light brown; frontal margin V- shaped; dorsal setae 25-35 [micro]m, 1.
Head light brown; frontal margin subrectangular; dorsal setae 2023 [micro]m and 0.
Head light brown, with brown spots in front of eyes; frontal margin deep V-shaped; dorsal setae 35-50 [micro]m,1.
Head light brown; frontal margin deep V-shaped; dorsal setae 42-53 [micro]m, 1.
Pronotum relatively flat, frontal margin
of pronotum slightly projecting as obtuse triangle; median carina completed, lateral carinae parallel on prozona, the prozona nearly square; humeri forming an obtuse triangle, with a pair of abbreviated carinaes between humeri.