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Sept 20 (Reuters) - Credit default swap indexes measuring the cost of insuring against European corporate bond defaults jumped on Monday to the highest since late-May, driven by a combo of global risk aversion and a monthly change in benchmark constituents.

The iTraxx European Crossover index, which measures the cost of insuring exposure to a basket of sub-investment-grade European companies, jumped as much as 27 basis points to 253 bps, the highest since late-May.

The iTraxx Europe index, which measures the cost of insuring against default on investment-grade corporate bonds, rose seven basis points to 51 bps, also the highest since late May.

Both indexes were set for their biggest daily jumps since mid-March.

One investor said much of the rise was caused as the indexes "rolled" to a new series, a move that can cause large daily moves on the first day of trading, as companies comprising the index change.

Falling commodity prices, unease ahead of Wednesday's U.S. Federal Reserve meeting and worries around Chinese property company Evergrande were also behind the rise, fuelling a selloff in equity and credit markets.

(Reporting by Yoruk Bahceli; editing by Dhara Ranasinghe)