PA31 or PA-31 may refer to:

• Pennsylvania's 31st congressional district
• Pennsylvania Route 31
• Piper PA-31 Navajo light aircraft

• Xestia homogena
• Xestia homogena conditoides
• Xestia hyperborea
• Xestia hypographa
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• Xestia kollari
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• Xestia lorezi
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• Xestia normaniana
• Xestia normanianus
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• Xestia praevia
• Xestia quieta
• Xestia renalis