Tree-eating beetle spreading across U.S. West

Matt Johnson treks along an Arizona riverbank and picks out a patch of yellow-tinged tamarisks. He sweeps a cloth net across the trees, hoping to scoop up beetles that munch on their evergreen-like leaves.

He counts spiders, ants and leafhoppers among the catch and few beetles or their larvae.

“Their numbers are really low,” the Northern Arizona University researcher said.

That the tiny beetles brought to the U.S. from Asia in an experiment to devour invasive, watersucking tamarisks showed up at the Verde River in central Arizona is no surprise. But it’s further evidence they’re spreading faster than once anticipated and eventually could pervade the Southwest U.S, raising wildfire risks and allowing less time to uproot the tamarisks, also called salt cedars, and replace them with native trees.

Without those efforts, an already highly flammable tree will burn more intensely, and an endangered songbird that nests in tamarisk might not have a home.

The federal program to use the beetles to chew up tamarisk trees began as an experiment in rural Nevada in 2001 and was approved for more widespread use in 2005, as long as they were at least 320 kilometres from Southwestern willow flycatcher territory. It ended in 2010 as the beetles intruded on the birds’ habitat. An unintentional release in southern Utah also helped the insects spread into Arizona.

Johnson believes the 6 mm beetles hitchhiked to the Verde River on clothing, a backpack or a boat. Normally, they are wind travellers but would have had to catch quite a gust to get to the river from the closest drainage where they’ve been recorded, he said.

Johnson has sent samples to a geneticist in Colorado to determine if the beetles can be traced to a population north of Arizona or a subtropical one from Texas that multiplies quicker.

Arizona once was projected to be too hot for the beetles to survive, but they’ve evolved as they’ve expanded their reach. Dan Bean with the Colorado Department of Agriculture found even more this summer in far southwestern Arizona along the California border, where temperatures regularly top 38 C.

The concern now is the beetles establishing themselves in the Gila, Salt and San Pedro watersheds, which have higher concentrations of flycatcher habitat.