Grinnell Mutual Reinsurance Co. has become the fifth Iowa insurer to agree to sponsor the planned Global Insurance Accelerator.  The company joins Principal Financial Group Inc., Delta Dental of Iowa, American Equity Investment Life Holding Co. and Farmers Mutual Hail Insurance Company of Iowa in supporting the new initiative, which will invest in insurance-related technology startups. Read more about the accelerator, which is to be launched this fall.