Tuesday, May 25, 2010

A Weevil for the Biological Control of Tamarisk

Since their introduction to the US from the Mediterranean and Asia several Saltcedar or tamarisk species, especially Tamarix ramosissima, developed into noxious weeds of riparian areas. In these valuable, but often fragile biotopes, tamarisks are replacing native willows, poplars and alders at an alarming rate with fast growing monocultures. So far there are no controlling natural enemies. In Arizona, solid stands of tamarisk can be seen for example at the Colorado River at Yuma and the San Pedro River at Benson.

Research and politics:
Researchers have studied tamarisks in Asia and Europe to find organisms usable as biological control of the spreading weed. Among the 'pests' that are tied to the tamarisk by close co-evolution in Asia and Europe (and thus would hopefully not attack any hosts other than tamarisk if introduced to the US), is the weevil Coniatus tamarisci. Efforts to get approval for its release here were underway for years, but were counteracted by naturalist groups mainly focused on birds because rare Willow Flycatchers are nesting in the tamarisk thickets. The United States Department of Agriculture claims not to have released the weevils from strict quarantine.

Field observations:
Last fall fellow arthropod researcher Jillian Cowles showed Charles O'Brien, our world expert on weevils, photos of a pretty little bug that she'd found on tamarisk bushes in Vail, Arizona. Charlie and Jens Prena recognized it as Coniatus splendidulus. This was the second time this species was found in the US, Charlie had received specimens from Phoenix, AZ in 2006.

So far we don't know how it got to the US. Could it have hitchhiked on a transport coming back from the war in Irak? This spring, it was found in Gilbert (Maricopa County), as well as along the Santa Cruz River from Marana (NW Pima County) to Amado (Santa Cruz County). The beetles fly well and will spread quickly, it seems.

Live Cycle: here's a video of a mating attempt

Mating pair in early May 2011

Adult beetles hibernate in soil and litter close to the trees. In Arizona, they climb the trees by the end of March, feed on fresh shoots, mate, and begin laying their eggs in early April. The image shows an unusually dark male competing for access to the female, and an egg in the lower right corner. Eggs are usually placed in a cavity that the female chews and then covered with the chewed material. Oviposition as shown here sometimes occurs in captivity or under stress.

From mid April to early May larvae were feeding on leaves and flowers together with the adults. They live free and unprotected on the surface of the plant, an unusual strategy in weevils.

When they are ready to pupate the larvae spin retinous web cocoons that serve as protective cages. They place them in the open at the tips of twigs, sometimes in clusters. Larvae, and then later pupae, can be seen wiggling inside through the loose mesh.

By mid May most have emerged as beetles. From Asia, Kovalev describes two generations per year. Here in Arizona there may be time for one more, or the beetles may take an aestivation pause during the dry hot season that's approaching.

At the Santa Cruz River the beetles seemed to prefer immature young trees. These hosts appeared clearly set back in their development compared to beetle free trees.

P.s.: Another tamarisk 'pest' the leaf beetle Diorhabda elongata is being released since 2004 in Utah and Colorado. Check this site for more info

P.p.s.: Diorhabda elongata, Trabutina mannipara (Mealybug) and Coniatus tamarisci were approved for release in 1996 Check here for more info. Only the leaf beetle was eventually released, but not in Arizona and New Mexico, where the Willow Flycatcher was found breeding in tamarisk.

April 2021: Coniatus splendidulus on a window screen in Oro Valley, Pima Co., AZ. Certainly no single occurrences anymore.

Kovalev, 1995, Co-evolution of the tamarisks (Tamariceae) and pest arthropods () with special reference to biological control prospects. Proceedings of the Zoological Institute of the Russian Academy of Sciences. St. Peterburg, vol. 259
Dudley, T.L. 2005, Progress and pitfalls in the biological control ofSaltcedar (Tamarix spp.) in North America. Proceedings 16th USDA interagency forum on Gypsy Moth and other invasive species


  1. Biocontrol civil disobedience?!

    Nice photodocumentation of the life cycle.

  2. Thanks, Ted. That would have been a nice title!

  3. I love that the beetle builds cages! How amazing!

  4. I'm enjoying your blog too, Margarethe. Nice job. BTW, it's the Willow Flycatcher that has been found nesting in the the tamarisk thickets in the Colorado River drainage. But they're no substitute for the former willows.

  5. Hi Margarethe! Thanks for reminding me to email now and then and to update my mollusc blog!
    Here the Black vine weevil (Otirhynchus sulcatus) is very good for biocontrol, because it's eating all thy ivy we had planted to cover the north side of our house!

  6. Hi Michael
    We could sure use those at our house in Kurl. Nothing keeps down that Ivy
    Good hearing from you

  7. Just had to add another "pest" of saltcedar. My son and I noticed house finches pulling off bits of the scaly leaves and eating them this winter. We presumed it was for the salt, but of course we don't know for sure.

    The birds did denude the small plant that had volunteered in our yard over a period of a couple of weeks.

  8. Hi Roberta
    I guess that's good news - with the birds themselves voting against the Saltcedar!

  9. Dennis Haines per e-mail said:
    Hi Margarethe,

    In California USDA and CDFA have released Diorhabda elongata (Chrysomelidae) for control of Tamarix ramossissima and T. parviflora. I am unaware of any releases of weevils in our state.

    Another possibility for how the weevils showed up suddenly is that someone decided to take matters into their own hands. For years in California Eucalyptus was pretty much a pest free tree. Then in the early 80's we began to find a new pest on the trees almost every year. Most were first found in Southern California and a number were first located near the campus of UC Riverside (coincidence?). Many environmentalist consider Eucalyptus as an introduced weed, especially in the coastal region. So some believe that one or more individuals are introducing these species to reduce the Eucalyptus populations.

    So maybe a non-birder got tired of waiting.


  10. From Dr. Chris Ritzi via e-mail

    Thank you for the link to the information on the salt cedar weevils. I have read about them in the past, but they had not be as heavily promoted as the Diorhabda beetles. I am currently working to establish and manage populations of the Tunsian variety of the beetles from Candelaria, TX (just 10 miles south of the 200 mile zone of the willow flycatcher), and south along the Rio Grande to Lajitas (just before entering Big Bend National Park). The beetles have been rather successful, and I am continuing to work with numerous groups and agencies to help control salt cedar in this region of Texas.

    Dr. Chris Ritzi

    Dr. Christopher M. Ritzi
    Chair and Assistant Professor
    Department of Biology, Box C-64
    Sul Ross State University
    Alpine, TX 79832

  11. I always wonder about these biological controls as I have often heard of them going awry. I hope this one works out and I am so surprised by the cage the larve spins!

  12. Hello Margarethe. I was finding these beautiful weevils on some of our sticky traps in El Centro Ca. A few weeks ago I had a black light on in my backyard and collected 20 plus of them. I have wanted to ID them since the first time I saw one. Thank you another mystery solved. I am all for the Willow Flycatchers but do not care for the invasive Salt Cedar at all. What a good little weevil.

  13. I'm happy to read that my blog is useful! If you have more mystery species of insects, why not post them on
    We'll be glad to figure it out for you!

  14. I would like to get some of the specimens being taken in El Centro, CA confirmed as the saltcedar weevil, Coniatus splendidulus. If this is not possible give the details as to where you have been collecting so I can drive down to El Centro and see if I can pick up a few of the for an official ID. I have been working on the biological control of saltcedar in northern CA and parts of the San Joaquin Valley for the past three years and I am always interested in hearing of what other species of insects are working on the saltcedar. Please contact me at sactorose@gmail.com

  15. Margarethe, I really like the photos you have posted of the Coniatus on Tamarix. You carefully pointed out that there is no evidence that its presence is at all related to the quarantine testing we were doing several years ago, but this bears repeating after noting a couple comments. We are finding it up in the Virgin River as far north as Utah, also around the Las Vegas.Lake Mead area, and in the lower Colorado River, so regardless of how they got here (probably many years ago), they are nicely established now and in a few spots are doing significant, but not extensive damage to invasive tamarisk. If you or correspondents have other locations records for Coniatus in No.. America, please let me know because we are trying to characterize their distribution. Really neat little guys!
    Tom Dudley
    UC Santa Barbara