BugGuide says:
Banasa dimidiata = Banasa dimiata (Say 1832)
Say's original spelling was dimiata, but the emendation dimidiata is now accepted by American workers.

EOL says:
Say (1831) originally described this species as Pentatoma dimiata, but LeConte (1859) emended the name to dimidiata. While some have accepted this emendation (Hoffman 2005), both names remain in use (Froeschner 1988).
http://eol.org/pages/609110/overview

By rules of nomenclature, dimiata is the valid name - by custom, we should use dimidiata here, because BG does.
(also, more observations under the last name on iNat)