The New York Stock Exchange is reporting a record number of insider-trading cases from 2008, but who is committing the alleged infractions is what’s raising eyebrows.

New York Stock Exchange Regulation referred 146 cases of suspected insider trading to the Securities and Exchange Commission in 2008, surpassing 2007’s numbers (another record year) by five cases. Especially notable, however, is the drop in suspected hedge fund involvement—down from 72 percent of the total in 2007 to 54 percent last year.

John Malitzis, head of market surveillance at NYSE Regulation, speculates that the drop may be a sign of the times. “With the ...