1	Cauda pale, most often with constriction at midpoint, with 4–7 setae. Antennae five or six segmented. Siphunculi pale, distally dusky. Summer morphs. Polyphagous (Figure 4E)	Aphid gossypii
–	Cauda dusky or dark	3
3	Siphunculi dark all throughout	4
–	Siphunculi dusky or lighter at the base	7
4	Cauda constricted	5
–	Cauda not constricted	7
5	Cauda spoon-shaped, distinctly constricted, with 4–7 setae. Ratios PT/B 2.6–4.1, SIPH/CA 1.3–2.5. Polyphagous (Figure 4D)	Aphid gossypii
–	Cauda slightly constricted	6
6	Cauda slightly constricted at midpoint, with 4–5 setae. Ratios PT/B 2.0–2.7, SIPH/CA 1.5–2.2. On Oenothera spp. (Figure 4K)	Aphid oestlundi
–	Cauda elongate, parallel-sided, with acute tip and slight constriction at the base, and with 4–8 setae. Ratios PT/B 1.8–2.5, SIPH/CA 0.9–1.6. On Hylotelephium spp. (and elsewhere recorded from Sedum spp. and some other Crassulaceae) (Figure 4G)	Aphid sedi
7	Siphunculi lighter at the base, dusky distally. Cauda tongue-shaped, with 6–9 setae. Ratios PT/B 1.7–2.9, SIPH/CA 1.3–1.7. On Monarda spp. (Figure 4I)	Aphid monardae
–	Siphunculi dusky. Cauda tongue-shaped, with 4–7 setae. Ratios PT/B 2.6–4.1, SIPH/CA 1.3–2.5. Polyphagous (Figure 4F)	Aphid gossypii