Purple-backed cabbageworm

Identification od Adults: forewing pale yellowish to light brown with sharp median and PM lines; ring-like marking in upper median area resembles a tied knot (a diagnostic feature); hindwing light gray with dark terminal band and partial PM line.
Season: adults fly from May to September; larvae present in August and September.
Food: larvae feed on bittercress, cabbage, radish, horseradish, turnip, and other plants in the mustard family.