July 8 (Reuters) - Wall Street"s main indexes fell sharply at the open on Thursday as the spread of the COVID-19 Delta variant cast doubts over an economic recovery, while a rout in Chinese tech stocks appeared to have spilled over across markets. The Dow Jones Industrial Average (.DJI) fell 112.8 points, or 0.33%, at the open to 34,569.01. The S&P 500 (.SPX) fell 37.1 points, or 0.85%, at the open to 4,321.07​, while the Nasdaq Composite (.IXIC) dropped 255.9 points, or 1.74%, to 14,409.19 at the opening bell.