US STOCKS-Wall Street dips; Apple gain fails to offset rate worries
* Fed's John Williams sees 2-3 rate hikes in 2016
* Yellen to speak later in the week
* Monsanto jumps after Bayer's $62 bln buyout offer
* Indexes end lower: Dow 0.05 pct, S&P 0.21 pct, Nasdaq 0.08 pct (Updates to close)
By Noel Randewich
May 23 (Reuters) - Wall Street ended lower on Monday as a bounce in Apple failed to offset concerns that the U.S. Federal Reserve could raise interest rates sooner than later.
The timing of future Fed rate hikes in the face of a sluggish economy is a major focus among stock investors who have benefited from historically low borrowing costs since the 2008 financial crisis.
The Dow Jones industrial average and the Nasdaq Composite traded higher for much of the session but they made a pronounced dip in the final few minutes.
San Francisco Fed President John Williams and his St. Louis counterpart, James Bullard, both struck hawkish tones in separate appearances on Monday. Continuación...