By Mica Rosenberg

(Reuters) - A bumble bee once common in the United States is disappearing so quickly it should be listed as an endangered species, environmentalists said in a lawsuit filed against U.S. government agencies on Tuesday.

The rusty patched bumble bee is now found in fewer and fewer areas as urbanization and agriculture reshape their traditional habitat on the Midwestern prairies, said the suit, which was filed in U.S. district court in Washington, D.C., against the Interior Department and the U.S. Fish and Wildlife Service.

Scientists ascribe the dwindling population to threats including disease, habitat destruction and pesticides, the environmentalists say.

"The leading hypothesis suggests that disease may be playing a role," said Sarina Jepsen, a program director at the Oregon-based Xerces Society, which brought the lawsuit along with the Natural Resources Defense Council.

Bumble bees pollinate a wide variety of plants and crops and are used commercially by farmers to help grow tomatoes in greenhouses. The wild species may have picked up diseases from non-native bees brought in by tomato producers, Jepsen said.

The rusty patched bumble bee is named for a distinctive rust-colored patch on its abdomen. While the exact size of the population is difficult to estimate, scientists say the relative abundance of the bee species has fallen 95 percent when compared with other types.

The Xerces Society petitioned the Interior Department to consider the endangered listing last year and decided to sue after receiving no response, Jepsen said.

The Fish and Wildlife Service said it could not comment directly on pending litigation but that it looks carefully at each petition to decide whether there is a need for more federal protections.

There are no bees currently listed as endangered species, although several Hawaiian yellow-faced bees are being considered for the designation, Jepsen said.

Honey bees, which are different from bumble bees and are widely used in agricultural production, have also experienced significant die-offs.

The U.S. Department of Agriculture is set to release its annual report on honey bee losses this week amid a fierce debate between environmental groups that cite pesticides as a main culprit and some in the chemical industry who say parasites and other factor are to blame.

The case is The Xerces Society v. Jewell et. al in the U.S. District Court for the District of Columbia, No. 1:14-cv-00802

(Reporting by Mica Rosenberg; Editing by Howard Goller and Steve Orlofsky)