Wall Street executives had a worrisome message for investors this week: The lack of client activity that sunk trading results in the second quarter has continued. JPMorgan Chase & Co., Citigroup Inc. and Bank of America Corp. are seeing declines ranging from 15 percent to 20 percent in the third quarter from the same period a year ago, executives announced at an investor conference hosted by Barclays Plc in New York. Goldman Sachs Group Inc. didn’t put a number on its performance, even as co-President Harvey Schwartz lamented “a pretty challenging environment” for fixed-income, currency and commodities trading.