By Jud Pyle, CFA, chief investment strategist for the Options News NetworkAetna ( AET) did not announce significant news today, but at least one investor is taking a bullish stance on the health insurance name and boosting call volume. The slightly out-of-the-money Nov. 31 calls have changed hands more than 20,000 times so far today and are home to current open interest of 311 contracts. The bulk of these calls traded at a price near 95 cents around 11:10 a.m. EST, when the stock was around $28. That computes to an implied volatility of approximately 47, compared to the 63-day realized volatility of 42. Given the premium of 95 cents, the buyer needs AET shares to expire higher than $31.95 to make money, unless of course, the calls rise prior to expiration following a rise in the shares and the investor chooses to sell them to take profit. Shares of Aetna have slid along with other HMO stocks like Cigna ( CI) and WellPoint ( WLP) over the last week and a half. AET and other stocks in the sector are down approximately 10% since the close on Sept. 21. One catalyst this call buyer could be banking on to get the shares moving upward again is AET's earnings report. The company is currently scheduled to announce results for its fiscal third quarter before the market opens on Oct. 29. Analysts are anticipating the company will make 66 cents per share, down from $1.12 in the same quarter 2008.