From The Colorado Springs Gazette (R. Scott Rappold):
…after two summers of releases here [Arkansas River Basin], the beetles have eaten little of their favorite food, and experts fear they are leaving, dying or becoming food themselves. “In most cases that I’ve seen so far, it seems like the beetles are gone and we’re trying to come up with ways to deal with that,” said Dan Bean, director of the state’s Palisade Insectary, where the beetles are bred…
In summer 2008, the National Resource Conservation Service released 27,000 beetles along Fountain Creek north of Pueblo. Last summer, after biologists found no trace of the beetles, they released another 15,000. “We did see a slight amount of defoliation, but it often takes a couple years for the beetles to take hold and establish,” said conservation service biologist Patty Knupp. She will return in spring to look for beetles.
Elsewhere in the Arkansas Basin, there have been only a few pockets with slight signs of beetles eating the tamarisk. Said Bean, “There could be some quirks in climate and weather that cause them to not make it, but I think it’s more likely it’s something biological. Something is eating them.” He suspects other insects are the culprit.
One the other hand here’s a story about a mystery population of the little buggers in Fremont County from October 2008. From the post:
On the drive back to Grand Junction after visiting Pueblo in July, Bean noticed the tamarisk at the U.S. 50 bridge over Beaver Creek were yellowing – a tell-tale sign of beetle defoliation. He stopped, and sure enough there was a thriving beetle population in the trees below the bridge. Where the beetles came from is anyone’s guess. The Bureau of Reclamation has, for years, done controlled releases of beetles on trees below Lake Pueblo, but Bean knows of no official releases of beetles upstream of Lake Pueblo. “If the conditions were just right, they could migrate upstream,” Bean said. The beetles were found in a rocky canyon, which is similar to the areas where the same type of insects have thrived in eastern Utah and Western Colorado.