Federal wildlife officials are proposing to remove a Sacramento Valley beetle from the endangered species list, citing improved population figures after more than three decades of protection.

The action concerning the valley elderberry longhorn beetle, a threatened species, was published today in the Federal Register and is expected to be formally announced tomorrow by the U.S. Fish and Wildlife Service.

The inch-long red and black beetle was nearly driven to extinction after more than 90 percent of Central Valley riparian habitat was eliminated by farms and levee building.

When it was protected by the Endangered Species Act in 1980, the beetle was found in only 10 locations throughout the Central Valley, including the American River in Sacramento and Putah Creek in Yolo County. Now it is found at 26 sites and benefits from more than 21,000 acres of protected habitat.

The beetle's primary habitat is valley elderberry bushes, which grow along streams and rivers. The plant itself is not endangered and is plentiful in many areas. But because of the beetle's threatened status, developers and flood-control agencies have been required to protect the shrub at great expense.

The Fish and Wildlife Service first hinted it might delist the beetle in a five-year status review published in 2006. But it never followed up with any action.

In 2010, the Pacific Legal Foundation, a Sacramento nonprofit law firm, petitioned the agency to delist the beetle on behalf of several property owners and flood control agencies. In March, it followed up with a lawsuit when there was still no decision by the service.

The Fish and Wildlife Service concludes that the beetle has reached sufficient numbers, and has enough protected habitat, to avoid extinction. It also reports that delisting should proceed despite the arrival of the Argentine ant, an invasive predator, because not enough is known about whether the ant will reduce beetle populations.

Marcel Holyoak, a professor of environmental science and policy at UC Davis, disagrees with this conclusion.

"It seems like a potential threat to the species," said Holyoak, an expert on the beetle who has also studied the ant threat. "We're sort of entering a more uncertain phase in what happens to the beetle."

The service will take public comments on the delisting proposal through Dec. 3. A final decision is then expected within 12 months.

© Copyright The Sacramento Bee. All rights reserved.

• Read more articles by Matt Weiser

Order Reprint