Insurers have been clobbered by a downgrade of the whole sector by Citigroup.RSA, Standard Life and Legal & General all retreat but it is insurance firm Old Mutual that is the main casualty after banking giant HSBC said is not going to go through with its proposed acquisition of a controlling stake in South African bank Nedbank from the insurer.HSBC said it is not in a position to make an offer for Nedbank as due diligence on the deal resulted in unexpected difficulties.Gearbox designer Hansen Transmissions International leads the alternative energy sector higher after saying it is to sell its loss making industrial gearbox division to concentrate on wind turbines.Top performing sectors so far todayAlternative Energy 3,345.41 +9.72%Fixed Line Telecommunications 1,994.64 +1.25%Media 3,929.69 +0.56%Aerospace and Defence 3,462.09 +0.49%Forestry & Paper 5,902.70 +0.46%Bottom performing sectors so far todayInsurance (non-life) 1,503.72 -1.19%Life Insurance 4,088.49 -1.04%Personal Goods 17,052.06 -0.84%Software & Computer Services 664.59 -0.84%Health Care Equipment & Services 3,077.31 -0.82%