Tamarisk-eating beetles still doing their job, officials say

More than a decade after first being introduced as a biological means of controlling the proliferation of tamarisk plants in Grand County, tamarisk beetles are still doing their job and doing it well, officials say.

And despite concerns to the contrary that have been raised by some local residents, the tamarisk beetles continue to feed exclusively on the plants they were brought in to destroy, officials add.

“It seems like every year, we get a few reports of tamarisk beetles eating other vegetation, and we go out and investigate them, and it’s always something else,” said Tim Higgs, Grand County’s weed control supervisor.

Higgs said tamarisk beetles are occasionally confused with other insects, including the cottonwood leaf beetle.

“They have been studied more than any other [means of] bio-control over the past 20 years,” Higgs said of the species of beetles, which are also known as salt cedar beetles and have the Latin name Diorhabda carinulata.

Michael Johnson of Utah State University’s extension office in Moab said that he also fields occasional calls about tamarisk beetles, and also confirmed that research has repeatedly shown that the beetles exclusively feed on tamarisk leaves, and no reliable evidence has yet indicated otherwise.

A few area residents had expressed recent concerns that the tamarisk beetles were harming plants in their yards. One Spanish Valley resident said they were feeding on his Datura plants, while another man in Castle Valley reported having to spray his cottonwood trees, which he said were being eaten by beetles.

Such situations are almost certainly the fault of other insects, Higgs said, adding that it is rare for the tamarisk beetles to stray more than a mile from the tamarisk plants that serve as both their home and food source throughout their life cycle. In Grand County, tamarisk plants are primarily found lining the shores of the Colorado River and the streams that feed into it, such as Pack Creek and Mill Creek.

More than a decade ago, Higgs oversaw the introduction of the beetles in Grand County, which was part of a program authorized by the U.S. Department of Agriculture. Over a three-year period from 2004 to 2006, beetles were released at 11 target sites along the Colorado River in Grand County, with one to three releases being made at each, and 10,000 adult beetles released at each time, Higgs said.

Higgs said that the initial cost of the tamarisk beetle release was about $5,000 to $6,000 over that first three years, but the county has already reaped a huge return on its investment.

“It would cost millions of dollars to do what these beetles have done,” Higgs said, noting that many of the targeted areas have seen decreases of 80 percent or more in green tamarisk plants. In addition, more than a dozen species of desirable native riparian plants, including willows, have been re-establishing themselves underneath the dead and dying tamarisks, Higgs added.

In the decade since the beetles were introduced, research has shown a notable reduction of tamarisk in many areas throughout the western United States and northern Mexico.

Still, the program is not without potential risks, some conservationists have noted.

“Biological control may assist in the long-term recovery and resiliency of riparian communities, but potential short-term consequences cannot be disregarded,” cautions a summary article posted on the website of the Tamarisk Coalition, a non-profit organization dedicated to the restoration of riparian lands.

Although the group advocates the use of tamarisk beetles as a positive and effective tool in combating the spread of tamarisk, some of the potential drawbacks cited by the coalition include negative impacts on the habitats of certain species of birds, such as the endangered Southwest willow flycatcher, in addition to other problems associated with dead biomass and riverbank destabilization.

The coalition monitors the spread of the tamarisk beetle populations in the southwestern U.S., and posts annual maps and other data on its website.

Higgs said one other notable example of local bio-control involves the use of gall midges to control the spread of Russian knapweed in Grand County. That program, which started in 2013, is already starting to see noticeable success, he said.

For more information, Higgs may be reached at his office at (435) 259-1369. Johnson may be reached at the USU Extension office (435) 259-7558. Real-time tracking of invasive species can be accessed at www.eddmaps.org and its associated cell phone apps, which are used by various governmental agencies.

ByBy Jeff Richards

Contributing Writer