U.S. property/casualty insurers’ aftertax net income dropped 70.5% to $7.98 billion during the first nine months of this year compared with a year earlier, according to a survey released Monday by the Insurance Services Office Inc. and the Property Casualty Insurers Assn. of America. Inc. The survey found that P/C insurers’ net underwriting losses grew to $34.91 billion during the first nine months of 2011 from $6.30 billion during the same period of 2010.