The Xerces Society of Invertebrate Conservation and the National Resources Defense Council (NRDC) filed a notice of intent to sue to US government for failure to meet its legal requirement to respond to a petition to list the rusty-patched bumblebee as an endangered species under the US Endangered Species Act.

The move comes after the rusty-patched bumblebee (Bombus affinis) was listed as an endangered species in Canada, becoming the first bee species in North America to be on a federal endangered species list.

The Xerces Society's 42-page petition to list the bee on the US Endangered Species List was sent to then-Secretary of the Interior Ken Salazar on Jan. 31, 2013. (Salazar resigned in April 2013 and was succeeded by Sally Jewell.)

According to the Xerces Society, perhaps the most influential bee conservation group in the US, the rusty-patched bumblebee - named so because of the rust-colored patch on its abdomen - was once common throughout the east and upper Midwest region of the US. Now the bee's numbers have declined by 87 percent across its historic range.

"The charismatic and once common rusty patched bumble bee has suffered severe and widespread declines throughout its range in the eastern US since 1997," said bumblebee expert Robbin Thorp, professor emeritus of the University of California, Davis. Thorp is coauthor of the petition to list the bee as an endangered species. "The few scattered recent sightings thanks to intensive searches are encouraging, but the species is in critical need of federal protection," he said in a statement last year.

Sarina Jepsen, endangered species program director at the Xerces Society said the remaining populations of the rusty-patched bumblebee are small and isolated and "continue to be threatened by diseases from a largely unregulated commercial bumble bee industry, as well as by disease from other sources, habitat degradation, pesticide use and climate change."

The conservation group is suing the Department of the Interior for failing to recognize or respond to its petition to get the rusty-patched bumblebee recognized under the Endangered Species Act (ESA).

In a statement Thursday, the conservation group said:

"The Xerces Society filed a petition to protect the rusty patched bumble bee under the ESA more than a year ago. Under the ESA, the Secretary of the Interior must make an initial response to a petition within 90 days (a simple statement of whether or not the petition presents sufficient information to support the requested protection), and if the Secretary finds that protection may be warranted, this law further requires her to decide within a year of the petition whether or not the species should be protected . Neither of these deadlines has been met, hence the Xerces Society and NRDC are taking the next step."

Read more about the rusty-patched bumblebee at the Xerces Society.