Researchers previously thought that this species of the tamarisk leaf beetle would restrict its range to above the 38th parallel, which is near the upper end of Lake Powell. The beetles were not approved for release within 200 miles of southwestern willow flycatcher habitat, an endangered species which is known to nest in tamarisk - a dominant species in the Colorado River corridor. Tamarisk leaf beetles are now causing defoliation of tamarisk trees further south than originally anticipated. According to Dr. Dan Bean of the Colorado Department of Agriculture, the small population of beetles recently documented in Grand Canyon National Park is unlikely to overwinter successfully. However, it appears likely that as beetle numbers increase a viable reproducing population will be established in Grand Canyon within the next several years.Good news or bad? I'd come down tentatively on the side of good. After all, the whole point of the beetle program is to get them out there eating tammies, and if they're able to do it down south it could be very good for a lot of places I love. But it was somewhat comforting to think that they had geographic limitations.
Reporting on the beetle program is generally rather confused; I never seem to read the same details twice. Tamara Naumann, the park botanist for Dinosaur National Monument and a major driving force behind the beetles, told me this summer that there are actually two species in the mix: the northern-adapted one that was released in Dinosaur, and a more southerly version released (if I remember correctly, which I may not) by the state of Colorado. She also said that there are apparently beetle poachers who are collecting some from release sites and taking them elsewhere.
It's been nice during the last couple seasons in Dinosaur to see some decidedly ratty tamarisk stands. It apparently takes three or four good defoliations to kill the damn trees, so with any luck we'll start seeing real death in the next year or two. Of course, being a biologic control, the beetles are not expected to eliminate tamarisk completely, and then go rampaging about for other things to devour. The best case scenario is that the tammy populations will crash, followed by a beetle crash, followed by a tamarisk rebound, etc. The hope is not that the trees will be eliminated, but that the beetles will bring them under sufficient control that native plants can start competing again and other removal methods will become feasible at select sites. Virtually the only Achilles heel of tamarisk is that it doesn't like shade; there's a hope that if box elders and other natives can get saplings establishes, they may be able to shade out the tammies in places.
If you've just tuned in to this story, I should mention that the decision to use biologic controls was not made lightly. The people behind it, believe it or not, are aware of the risks, disastrous historical precedents, and probably even the relevant Simpsons episode. The decision to release follows over twenty years of lab study, the most intensive study on a biologic control ever. The beetles are very tamarisk specific. Tamarisk has no North American relatives at the genus level, and its only relative in the same family lives in very different (i.e. non-riparian) habitat. The risk is there, but it's low, as low risk as a biologic control can ever be.
Ms. Naumann is humble regarding the introduction, and aware that "future generations may curse my name." She has also worked against other biological control projects where the outlook was more dubious. But she likes to point out that doing nothing was a choice as well, a choice whose consequences were predictable and disastrous, given the high value of the riparian habitat that tammies invade. Of particular concern in Dinosaur are the tammies moving up the Yampa canyon to invade some of the very last cobble bars where the highly-endangered native fish spawn. Introducing the beetles was a calculated risk ; leaving things be was guaranteed to be lousy.
Click here for dystopian tamarisk sci-fi, by a Paonia, CO author.