Retail investors have accounted for as much as 25% of the stock market's activity amid coronavirus-driven volatility, Joe Mecane, the head of execution services at Citadel Securities, said in an interview on Bloomberg TV on Thursday. The group made up just 10% of the market in 2019. The proportion steadily climbed as brokers slashed commission fees and the pandemic fueled violent price swings. The growing popularity of options trading reflects an increase in retail investors' knowledge and access to complex investment products, Mecane said. Still, the group isn't throwing the market out of whack.