EMC Insurance Group Inc. on Wednesday announced that its first-quarter operating results, which it will release May 10, will be negatively affected by a high level of catastrophe and storm losses and a significant decline in additions to its reinsurance reserves.The Des Moines-based insurer anticipates first-quarter earnings in the range of 5 cents to 1 cent per share. The company also lowered its 2011 operating income guidance. The company also announced that losses associated with the Mapleton tornado and related weather events in Kansas and Oklahoma are estimated at approximately $4.8 million, or 24 cents per share after tax. Those losses will be reflected in its second-quarter results.