Key to the species of Belostomatidae from northeastern Brazil

The key includes characters previously used to recognized species of Lethocerus from Perez-Goodwyn (2006) and Belostoma from Lauck (1964), Estévez & Polhemus (2007), Ribeiro (2007), Ribeiro & Alecrim (2008), Ribeiro et al. (2017), and Stefanello et al. (2021).

1. Sternites IV–VI subdivided laterally by a suture-like fold (Perez-Goodwyn 2006: figs 30–31); labium short, with second article thicker than long.....................................2 Lethocerus Mayr, 1853

– Sternites IV–VI not subdivided; labium long, with second article longer than thick (Stefanello et al. 2021: fig. 1A)...........................................................................................4 Belostoma Latreille, 1807

2. Ventromesal projection of hind tibia pointed (Perez-Goodwyn 2006: fig. 4); body length 90 mm or more ......................................................................................... Lethocerus maximus De Carlo, 1938

– Ventromesal projection of hind tibia rounded (Perez-Goodwyn 2006: fig. 3); body length less than 70 mm ................................................................................................................................................ 3

3. Parasternites III–VII with longitudinal dark stripe (Fig. 14); prosternal keel pointed at the apex (Perez-Goodwyn 2006: fig. 38) .............................................. L. annulipes (Herrich-Schäffer, 1845)

– Parasternites III–VII without longitudinal dark stripe; prosternal keel rounded at the apex (Perez-Goodwyn 2006: fig. 37).......................................................................... L. delpontei De Carlo, 1930

4. Eye triangular, lateral margins straight or slightly rounded (Stefanello 2021: fig. 1C–D)................ 5

– Eye globose, lateral margins rounded................................................................................................ 9

5. Anteoculus longer than interoculus; body length 40–52 mm ............................................................ 6

– Anteoculus as long as interoculus (Stefanello 2021: fig. 1C); body length 21–28 mm .................... 7

6. Ventral abdominal pilosity covering entirety of connexivum (Fig. 7)................................................. .................................................................................................. Belostoma dilatatum (Dufour, 1863)

– Ventral abdominal pilosity covering only half of connexivum (Fig. 8) .............................................. ................................................................................................................ B. gestroi Montandon, 1900

7. Ventral abdominal pilosity covering entirety of connexivum and part of sternites (Ribeiro 2007: fig. 2E) .................................................................................................. B. costalimai De Carlo, 1938

– Ventral abdominal pilosity not covering entirety of connexivum and not covering sternites (e.g., Figs 3, 5 and Ribeiro 2007: fig. 2A) .................................................................................................. 8

8. Metaxiphus with a carina-like structure developed along mesal part; lateral folding of the pronotum broad, extending up to the posterior part ....................................................... B. bosqi De Carlo, 1932

– Metaxiphus with proximal part elevated and distal part swollen; lateral folding of the pronotum narrow, not extending up to the posterior part................................... B. discretum Montandon, 1903

9. Vertex, pronotum, and posterior part of scutellum with distinct carina; vertex straight below the ocular line; eye small, interocular space> 1.7× eye width ............................................................. 10

– Vertex, pronotum, and posterior part of scutellum without distinct carina; vertex prominent above the ocular line; eye large, interocular space <1.6× eye width .........................................................11

10. Body narrow, ratio length/width about 2.3×; lateral margins of body almost parallel; length of anteoculus 0.88–1.13 × length of interoculus ........................... B. aurivillianum (Montandon, 1899)

– Body broad, ratio length/width about 2.0×; lateral margins of body slightly convex; length of anteoculus 1.15–1.59 × length of interoculus .............................. B. stollii (Amyot & Serville, 1843)

11. Body 10–20 mm in length; prosternal keel not elevated (Ribeiro 2007: fig. 12A–B); anteoculus shorter than interoculus.................................................................................................................... 12

– Body 28–52 mm in length; prosternal keel prominent, with apex rounded (Ribeiro 2007: fig. 7A–C); anteoculus longer than interoculus .................................................................................................. 16

12. Ventral diverticulum straight distally, in lateral view (Ribeiro 2007: fig. 11G–I); diverticulum broad ................................................................................................................................................ 13

– Ventral diverticulum curved downward, in lateral view (as in Figs 35, 37); diverticulum elliptical .. ......................................................................................................................................................... 14

13. Body 13–16 mm in length; ratio length/width about 2.35, narrow species; dorsal arms of phallosoma straight, covering lateral margins of diverticulum............ B. amazonum Estévez & Polhemus, 2001

– Body 17–19 mm in length, ratio length/width about 2.15, elliptical species; dorsal arms of phallosoma slightly convergent, not covering lateral margins of diverticulum ...... B. horvathi Montandon, 1903

14. Body more than 13 mm in length; prosternal keel prominent...................... B. plebejum (Stål, 1860)

– Body 10.5–13 mm in length; prosternal keel not prominent........................................................... 15

15. Diverticulum of phallosoma with strong, median dorsal depression, dorsal arms of phallosoma divergent (Ribeiro 2007: fig. 12C–E) ...................................................... B. micantulum (Stål, 1860)

– Diverticulum of phallosoma with slight, median dorsal depression, dorsal arms of phallosoma abruptly convergent (Ribeiro & Alecrim 2008: fig. 4) ......... B. nessimiani Ribeiro & Alecrim, 2008

16. Body narrow, elongate; diverticulum of phallosoma with lateral margins sinuous, broader basally than apically (Ribeiro et al. 2017: figs 32, 52) ................................................................................ 17

– Body elliptical; diverticulum of phallosoma evenly elliptical......................................................... 18

17. Ratio basal/apical width of ventral diverticulum about 2.3× (ventral view), dorsal arms divergent (Figs 32–33)...................................................................................... B. elongatum Montandon, 1908

– Ratio basal/apical width of ventral diverticulum about 2.0 × (ventral view), dorsal arms more parallel .................................................................................................... B. foveolatum (Mayr, 1863)

18. Clypeogenal cleft longer than clypeoloral cleft............................................... B. harrisi Lauck, 1964

– Clypeogenal cleft as long as clypeoloral cleft (Stefanello et al. 2021: fig. 1D).............................. 19

19. Prosternal keel narrowly rounded to acute (Fig. 24); dorsal arms of phallosoma broad (Fig. 30) (Ribeiro et al. 2017: figs 39–43); body length about 42–50 mm ............... B. dentatum (Mayr, 1863)

– Prosternal keel rounded; dorsal arms moderately slender; body length about 29–35 mm .............. 20

20. Ventral diverticulum of phallosoma twice as wide as long (ventral view), ventroapical protuberance poorly developed (Fig. 29) ........................................................ B. anurum (Herrich-Schäffer, 1848)

– Ventral diverticulum of phallosoma 1.3× as wide as long (ventral view); ventroapical protuberance well developed............................................................................................ B. dallasi De Carlo, 1930