JOHANNESBURG (Reuters) - South African insurer Sanlam reported little earnings growth for the first 10 months of the year, saying its investment returns were significantly weaker than a year earlier, which sent its shares sharply lower. South Africa's biggest insurer by market value also said that the state-owned pension fund, the Public Investment Corporation, withdrew 10 billion rand ($891 million) from its funds during the period. Diluted headline earnings per share rose by 4 percent. A year ago, earnings increased by 35 percent. "Overall investment market returns during the first 10 months of 2014 were significantly weaker than the comparable period in 2013, dampening growth in headline earnings per share," Sanlam said in its operational update. Sanlam said it booked new business of 150 billion rand, a 17 percent increase from a year ago. Its shares were down more than 5 percent at 1429 GMT, its biggest one-day drop in a year and a half. (1 US dollar = 11.2040 South African rand)