Apple’s shares are sliding Monday in the wake of a report in The Wall Street Journal that the company has reduced parts orders for its iPhone 5 amid slumping demand.

The stock  AAPL -2.77% fell below $500 briefly and was off $16.80, or 3.2%, to $503.50 in recent trading.  That would be the worst percentage decline for Apple , since a 3.8% slide on Dec. 14. Apple last closed below $503.50 on Feb. 17, 2012, when it ended the day at $502.12.

The company’s slide is hitting major indexes. Apple accounts for 3.8% of the S&P 500 index  SPX -0.22% which is down 0.4% to 1,466 in recent action. The share slide has taken as much as $17 billion off the S&P 500′s valuation.

It’s also weighing heavily on the Nasdaq COMP -0.42% where it accounts for 10% of the index value. The Nasdaq is off 0.66% at 3,105 in recent action.

Apple’s worst day in the past 12 months was Dec. 5, when it fell 6.4%.

– Tom Bemis