Image copyright AP Image caption The yellow-faced bee was once abundant across Hawaii

Seven species of yellow-faced bee native to Hawaii have become the first bees to be added to the US federal list of endangered and threatened species.

Conservationists say the bees face extinction through habitat loss, wildfires and the introduction of non-native insects and plants.

The bees are crucial to pollinating some of Hawaii's endangered plants.

The listing follows years of study by researchers including the Xerces Society conservation group.

Sarina Jepson, director of endangered species and aquatic programmes for Xerces, said although yellow-faced bees are found elsewhere in the world, the species now under protection are native only to Hawaii and pollinate indigenous plants.

While those species could potentially be pollinated by other bees, she said many could become extinct if the native bees were allowed to die off.

She told the Associated Press news agency that threats to the bees include feral pigs and invasive ants.

The bees had also suffered loss of habitat due to wildfires, invasive plants and land development, especially in some coastal areas, she added.

Hawaii-based entomologist Karl Magnacca, who worked with Xerces, said it had taken almost 10 years to achieve the listing.

"It's good to see it to finally come to fruition," he said.