Co-Occurrence of the Saltcedar Leaf Beetle (Diorhabda elongata)
Steven Schafersman, Ph.D.
This brief report documents the co-occurrence of Diorhabda elongata, the Saltcedar Leaf Beetle, and Coniatus splendidulus, the Splendid Tamarisk Weevil, at the I-20 Wildlife Preserve in Midland, Texas. The report contains photographs that documents the first discovery of the Splendid Tamarisk Weevil at I-20 and the co-occurrence of both types of beetles. The official popular name of the Saltcedar Beetle species is the Mediterranean Tamarisk Beetle; there are at least five species of Diorhabda Saltcedar Leaf Beetles, each with its own popular name; three different species have been released in Texas; all are difficult to tell apart without either DNA analysis or male genital dissection. The saltcedar leaf beetle and tamarisk weevil were both found on the saltcedar (also popularly known as tamarisk) that grows in the I-20 Preserve, an urban playa and its surrounding habitat. Presumably, the species Diorhabda elongata was intentionally released at the Preserve in June 2013 by the Texas Parks and Wildlife Department (TPWD) with the permission of the I-20 Preserve administration. Saltcedar (Tamarix ramosissima) grows abundantly at the I-20 Preserve because of the high water table and common presence of water runoff from the city. Chemical treatment and physical removal in 2008 and subsequent years were only partly successful in mitigating the growth of saltcedar, a notoriously invasive and noxious plant that transpires an excessive amount of groundwater that lowers the water table and damages the natural riparian and playa environments. Saltcedar Leaf Beetle mating and single adults, larvae, and eggs were observed and photographed by the author and Dr. Gae Kovalick, Associate Professor of Biology at the University of Texas of the Permian Basin, on 2014 April 12 at I-20 Wildlife Preserve.
The Splendid Tamarisk Weevil was not intentionally released. Rather, it was first accidentally introduced in Arizona and has now migrated to several southwestern states, including West Texas. Splendid Tamarisk Weevil pupal cases had been observed and photographed on saltcedar along Monahans Draw in 2012, but their identity was not yet understood. Both weevil larvae and pupal cases were first observed and photographed at I-20 Wildlife Preserve on April 12 by the author and Dr. Kovalick. They were not immediately identified as Splendid Tamarisk Weevil developmental stages but all were identified successfully the next morning because we had access to extensive biological reference resources and knew what we were looking for. Adult weevils were not observed despite a careful search but I expected to find them soon. Indeed, many adults were later collected at I-20 and several nearby sites along Monahans Draw in Midland County and along Beals Creek in Big Spring. This species is a true invasive that has never been rigorously tested as a danger to native plants as D. elongata has been, so it is not known what its final effect will be on the West Texas flora. For now, it appears to be restricted to salt cedar.
Biological Control of Saltcedar with Tamarisk (Saltcedar) Beetles
Texas has a mature program of biological control of Saltcedar using Saltcedar Leaf Beetles (only a few references and citations are provided in this brief report, but visit http://bit.ly/1kvmWkt for a good list). Foreign animals intended for biological control are not released in the U.S. unless an extensive testing program is conducted to be certain that they won't eat non-target plants. So far, such programs have been successful for use against invasive plant pests (the same is not true for biological control of animals; in fact, many--perhaps most--releases of non-native animal control agents have been disasters and entire ecosystems have suffered). The release of three species of Saltcedar Leaf Beetles in Texas and other Southwestern states has been extremely successful. Particular species of Diorhabda released are chosen to match the climate of the region they are to be used. For example, the species D. elongata was released in 2004 in Big Spring, Texas, very near to Midland, so the author assumes this is the species that was released in Midland (the species all look very similar and are difficult to determine despite the presence of side-by-side photos; only DNA and dissection of male genitalia can successfully be used to determine these separate species).
Three species of Tamarisk Weevils, Coniatus splendidulus, C. repandus, and C. tamarisci, were briefly studied as potential biological control agents for United States saltcedar, but they were never fully tested in the appropriate manner for a foreign introduction (this process takes years and is expensive), because the Diorhabda spp. beetles had already been shown to be quite successful and safe as biological control agents, and were therefore selected for the biocontrol program. Therefore, no one knows if the Tamarisk Weevil will eat other native plants in the U.S. Their presence now in the U.S. has been suggested (http://bit.ly/1nLK3rJ) to be the result of transport from Iraq on repatriated military equipment sent to Arizona (the first state to have the weevils), but this explanation is ludicrous for several reasons. The hypothesis that the weevil was introduced by contamination of Diorhabda spp. beetle stocks released in Arizona in 2006 or earlier is much more probable. The weevils are now found in Arizona, southern California, southern Utah, Colorado, New Mexico, and West Texas (http://bit.ly/QDLeyB). In other words, the weevils are found in all the same places that the saltcedar leaf beetles are found, coexistent with the presence of saltcedar (tamarisk).
The Big Spring release was a considerable success as surveys in the summer of 2009 showed. I have long been interested in the concept of using insects for biological control of plant pests and wanted to photograph and study the Saltcedar Beetles. I learned, after the fact, that the beetles had been released in the I-20 Wildlife Preserve and was disappointed that I was not informed and missed the event. I wrote a brief article about the beetle and the local release for a natural history newsletter in November 2013 (http://bit.ly/1f9sJgJ). Fortunately, the TPWD wildlife biologist who performed the release, Annaliese Scoggin, was the instructor at a Texas Master Naturalist class I attended on 2014 April 12. She told me that she had visited the I-20 Wildlife Preserve the day before and the Saltcedar Beetle adults had emerged from the ground (where their pupae stay during the winter) and were present and active on the saltcedar. So that very afternoon I visited the preserve to photograph the beetles. I had no trouble finding them and, despite a strong wind, photographing them with the cameras and powerful macro lenses I use to photograph butterflies.
Here are three photographs of the Saltcedar Beetle adults (click on any photo in this report for the full-size version):
I watched these eat the saltcedar, move, and mate. They would drop off the saltcedar branch if I jostled them too much (many insects exhibit this escape behavior).
I also found plenty of Saltcedar Beetle egg masses:
I knew what all these were because I had studied the Saltcedar Beetle literature abundantly available on the Web and several of these had good macrophotographs that made the several stages of metamorphosis easy to identify. In 2013 November I prepared a list of Saltcedar Beetle literature references at http://bit.ly/1kvmWkt. For example, here is diagram that is a good summary:
However, I also found things I did not expect. For example, I found several of these ellipsoidal sacs or cases that had a reticulated, porous, latticework-like exterior:
Even more interesting, I found two different larvae eating the saltcedar, one next to a Saltcedar Beetle egg mass, but I knew they weren't Saltcedar Beetle larvae which are quite distinctive:
Saltcedar Beetle larvae have longitudinal black and yellow stripes (one is pictured in the diagram above), so what could these yellow and green larvae be? I observed both larvae; they were moving slowly and both were eating the saltcedar. I took many other photographs of their movements, but they are not focused well enough to meet my standards for publishing.
The next morning I had time to research these discoveries and found that the latticework cage-like pupal cases (for that's what they are) belonged to Tamarisk Weevils, no doubt the Splendid Tamarisk Weevil, Coniatus splendidulus, the only one identified to be in the U.S. Further investigation revealed that the two larvae, that look so dissimilar, are both Tamarisk Weevil larvae. The yellow one is the 1st instar larva and the green one is the 2nd instar larva. So I had photographed two different instar larvae of the same species, something I certainly did not suspect until later.
In the previous excellent video I referenced earlier (http://bit.ly/QDLeyB), the Colorado Mesa University biologist was able to determine using DNA studies that this Tamarisk Weevil did not come from Turkey (because she was able to obtain Turkish specimens of the weevil species and use its DNA to compare with U.S. specimens from Colorado, Utah, and Arizona). The U.S. invasive species could, however, have come from Southern Europe, Crete, North Africa, or Iraq (!), but more work is needed. The region of derivation of this weevil species, that was introduced and is now living in the U.S., would be very valuable information indeed, since it might help us discover how it got here.
I wrote and posted this report on April 18, but I returned to I-20 on April 24 to search for adult weevils to photograph. I couldn't find any, but I did discover some broken and empty pupal cases. They were on saltcedar branches that had been denuded:
I photographed these using the wood boardwalk as a platform. The weevil pupa was still in one pupal case and it looked dead, but I put it in a jar just in case it "hatched" (it eats its way out). If it does that, I will photograph it and include it here (I will also kill and mount it for preservation, or send it to Colorado for DNA analysis). Here are some photos of Tamarisk Weevil adults, larva, and pupal cases from the Web:
I believe there is no question that, despite the absence of a photograph of an adult weevil, I have documented the occurrence of the Splendid Tamarisk Weevil at I-20 Wildlife Preserve and its co-occurrence with a species of Saltcedar Leaf Beetle.
Photographs of the Adult Splendid Tamarisk Weevil
I examined the saltcedar branch pictured above on 2014 April 30 and discovered that the pupa in the pupal case had completed its metamorphosis into an adult weevil and eaten through the pupal case. I immediately photographed it on the saltcedar branch and alone on white paper. Later I found it was not doing well; it probably needed saltcedar to eat. So I froze it in a vial and it will go into a -80 deg C freezer tomorrow so the DNA will be preserved. Rather than be mounted on a pin, it will be used for DNA analysis. I will collect more individuals for specimen display; for now the photographs will have to suffice. The scales below are in millimeters. The weevil is approximately 3 mm long.
The discovery and photographs of the adult Splendid Tamarisk Weevil
confirms beyond any doubt that this species occurs in the I-20 Wildlife
Written by Steven Schafersman Last update: 2014 April 30