Shares in UK insurer Prudential took a tumble on their first day's trading in Hong Kong speculation grew over the future of the chief executive of AIA, its takeover target.The FT reported this morning that Mark Wilson, AIA's chief executive, has told friends he will leave if the Pru's $35.5bn takeover of AIA, the Asian businesses of AIG, goes ahead. He reportedly described a merger of the two firms' Asian businesses as "unworkable".The Pru, which is in the middle of a $21bn rights issue to fund the AIA deal, watched its shares drop over 2.5% early on in Hong Kong.Although no new shares were issued today, Pru wants the listings in both Hong Kong and Singapore to win over Asian investors who are likely to play a key role in the upcoming rights issue."Our listings in Hong Kong and Singapore will provide us with a strong platform from which to continue to take advantage of the significant opportunities across the region," said chief executive Tidjane Thiam."These additional listings offer a wide range of investors the chance to invest in Prudential and confirm our increasing focus on Asia."But the debut came on a tough day when the Hang Seng index slumped 682 points, or 3.5%, to 18,985. It hasn't traded below 19,000 since July 2009.Pru shares traded as high as HK$59.85 and down at HK$56.60 before ending the session at HK$57.20.