The S&P 500 was down 0.5% in midday trading to 2,165.83.

The Dow Jones Industrial Average was down 0.4% to 18,372.73.

The NASDAQ was down 0.4% to 5,204.41.

The yield on a 10-year Treasury bond was down 0.7% to 1.56%.

The price of gold was down 0.4% to $1,311.

TECHNOLOGY

Newport Beach-based Clean Energy Fuels Corp. was down 6.2% to $4.32 and a $567 million market cap on above-average volume. The company runs natural gas filling stations.

Newport Beach-based Terra Tech Corp. was up 10.2% to 34 cents and a $117 million market cap on high volume. Shares of the hydroponic growing equipment maker were trading midday at three times its 90-day average.

SERVICES

Anaheim-based Willdan Group Inc. was up 2.2% to $16.90 and a $140 million market cap on high volume. The engineering services provider had by midday traded shares at a rate four times its 90-day average.

HEALTHCARE

Irvine-based ChromaDex Corp. was down 11.2% to $3.33 and a $126 million market cap on moderate volume. The company makes nutritional ingredients.