This one keys out to Prionyx parkeri. Even though Bohart & Menke's 1963 paper suggests that this species is the most common one with a red abdomen in the East, I thought it would be a good exercise to key it out from scratch. Here's the [il]logic:

Sphecini based on tarsal claws with "two or more teeth; second recurrent vein usually received by submarginal cell III" (1) => Prionyxina rather than Sphecina based on 2nd submarginal cell basal veinlet > apical veinlet; eyes not curving inwards towards ocelli. (2) => Prionyx rather than Palmodes based on more than 2 teeth on hind tarsal claw (1) => Prionyx thomae group based on "claws with four to five well-formed teeth", "male flagellum with fossulae" (2) => male based on 11-segmented flagellum, 7 visible abdominal segments (2) => abdomen partly red, erect body hairs white (2) => sternite 6 with broad U shaped median emargination; flagellomeres I and II together longer than IV (2) => Flagellomeres III-VI with fossulae (vs. III-V in P. canadensis) (2)

After all that, it would be nice to know whether I got it right. TIA