Key to species of Ambracius Stål

1. Pronotal calli with four yellowish spots; pronotum dark brown with two longitudinal yellowish stripes near sides (Fig. 2)......................................................................................................................................... A. capucinus (Reuter)

- Pronotal calli without yellowish spots; pronotum without two longitudinal stripes ................................................... 2

2. Anterior lateral margin of pronotum prominently carinate; scutellum with two median, longitudinal, black fasciae not reaching the apex; hemelytral membrane with two small black spots posterior to apex of cuneus (Fig. 9) ........... ...................................................................................................................................................... A. vittatus Carvalho

- Anterior lateral margin of pronotum not carinate; scutellum uniformly colored, without two longitudinal fasciae or with only one slender, longitudinal, black stripe; hemelytral membrane without two small black spots behind apex of cuneus .......................................................................................................................................................................... 3

3. Scutellum pale with a slender, longitudinal black stripe from base to apex; hemelytral membrane clear, with an irregular, fuscous, longitudinal band (Fig. 6a) .................................................................................. A. pallescens (Distant)

- Scutellum uniformly pale or black; hemelytral membrane mostly fuscous with apex whitish or pale brown, without stripes or bands ............................................................................................................................................................ 4

4. Clavus uniformly or predominantly fuscous to black; pronotum with a large longitudinal, black stripe widening from anterior to posterior margin or with a small to large black spot on disc; if stripe or spot absent on pronotum, clavus uniformly or predominantly fuscous to black (female of A. rubricosus) ..................................................................... 5

- Clavus uniformly or predominantly pale; pronotum uniformly colored or with two round, black spots on calli ....... 7

5. Scutellum uniformly black; corium without a transverse stripe (Fig. 5) .................................. A. mexicanus Carvalho

- Scutellum pale, not black, without stripes or spots; corium without a stripe or if present (Figs. 3a, 8b), scutellum uniformly or predominantly pale ...................................................................................................................................... 6

6. Head pale, with a fuscous band arising from margin of each antennal fossa and coalescing posteriorly on vertex; hemelytral membrane clear to pale brown, apex not white (Fig. 3a) .................................................... A. dufouri Stål

- Head without a stripe or band; hemelytral membrane fuscous, with the apex whitish (Fig. 8a–b) ............................... ................................................................................................................................................... A. rubricosus (Distant)

7. Pronotum uniformly reddish brown (Fig. 7a) .............................................................................. A. rudybuenoi, n. sp.

- Pronotum with two round, black spots on calli ........................................................................................................... 8

8. Hemelytral membrane mostly hyaline or pale brown (Fig.1a) .......................................................... A. alineae, n. sp.

- Hemelytral membrane fuscous to black, with inner margin bordering cuneus and apex whitish (Fig. 4a) .................. ............................................................................................................................................................... A. liviae, n. sp.