NEW YORK (Reuters) - Crop insurance firms are facing their worst losses in 15 years due to flooding in the US Midwest and higher commodity prices, said a Lehman Brothers analyst, who cut his second-quarter earnings estimates on some of the crop insurers.

Ace Ltd., XL Capital, PartnerRe Ltd. and RenaissanceRe Holding would be among the most-impacted companies, analyst Jay Gelb wrote in a research note to clients.

Mr. Gelb said several insurers had expanded in crop insurance to offset low growth in traditional property and casualty insurance.

Some experts estimated crop insured losses could be in excess of $3 billion in the state of Iowa alone, the analyst said.

l Property-casualty insurer Ace on Monday said it sees claims from the recent floods in the US Midwest having "negligible" impact on its second quarter and full-year earnings.

Ace is one of largest providers of crop insurance to farmers in the region, which has been hit by the worst flooding in 15 years, leading to concerns that producers could lose a significant portion of their crops.

Ace said it has federal reinsurance protection in place to pay part of the claims it receives, as well as reinsurance from the private market.

Insurers buy their own form of insurance, or reinsurance, to spread the risk of loss among more than one party. In the case, of multi-peril crop insurance, the government provides for some of that reinsurance.