P. grossa is identified vs. other Pepsis wasps as being the only species to have 12 antennal segments. Relative to P. thisbe, it is larger, has hairier legs, and from my own observation does not seem to have clear wingtips past the dark submarginal band of the forewing.

On a taxonomic note, I believe this species is now considered P. grossa, but would appreciate information regarding this.

Yikes... actually tried to key this one out using the resource cited below by Torre-Bueno (1939). Not sure if I messed up somewhere but I have the parts of the key I followed below as well. This species (assuming all one species) is very common on the globose flowerheads of Spermacoce verticillata and I decided to take a specimen now that I have a microscope.

"1. Spiracles of ventral segments III to VI below the lateral carina ....2"
(not super sure about this part, see last image)

"2.Apex of corium acute....11"
(this was the focus of photos 2-6, pretty sure it shows an acute (rather than rounded/obtusely pointed) corium)

"11. Pale markings of the corium widened near the base, extending over the cubital vein and almost filling the cell between cubital vein and the claval suture... 12"
I am interpreting pale as including the yellow/orange color. Not sure if that is too much of a stretch and shows that I messed up somewhere in keying this bug out! In any case, it is widened just after the base... right? (see photo 7)

"12. Male with the entire upper surface with uniform large deep punctures with narrow ridges between giving a honeycombed effect; hind margin of the hypopygium deeply concave emarginate; female with the entire upper surface with uniform deep punctures; length, less than 2.5mm"
Definitely less than 2.5mm as shown in first image. upper surface does seem to have large deep punctures with narrow ridges/honeycombed effect, but I might just be seeing that wrong. I did not try to figure out the hypopygium and honestly don't know if this is a female or male. (see photos 1, 7, 8)

Source:
Torre-Bueno, J. R. de la (José Rollin). (1939). A synopsis of the Hemiptera-Heteroptera of America north of Mexico. Part I. Families Scutelleridae, Cydnidae, Pentatomidae, Aradidae, Dysodiidae and Termitaphididae.Entomologica Americana (New Series), 19: Page 191