With energy stocks enjoying the biggest rebound since the beginning of the oil rout, short sellers have shifted their sights to regional banks that do business with the industry. Bearish bets have shot up 35 percent on average this year among the 10 most-shorted stocks in the KBW Regional Banking Index, data compiled by Bloomberg and Markit show. Cullen/Frost Bankers Inc. and Prosperity Bancshares Inc. in Texas have seen short interest surge about 60 percent. As oil prices plunged, concern over energy companies’ ability to pay back loans drove investors to unload or bet against financial stocks judged to have the most at stake in the sector. So far, the rebound that pushed oil to around $40 a barrel has done little to dilute that speculation. Stubbornly low interest rates are also squeezing profits in a group that trades at a premium of almost 40 percent to their larger […]