Diorhabda Elongata, a Eurasian Leaf Beetle, for Biologcal Control of Saltcedar

Release and Evaluation of Diorhabda elongata, a Eurasian Leaf Beetle, for Biologcal Control of Saltcedar. R. Carruthers1, J. DeLoach2, J. Herr1, P. Lewis2 T. Dudley3, J. Gould4 and N. Carruthers4

The USDA has initiated a biological control imple- 1 USDA-ARS, Albany, CA; 2 USDA-ARS, Temple, TX, mentation program for the exotic plant saltcedar. 3 Univ. of California, Berkeley, 4 USDA-APHIS, Phoenix, AZ Emphasis has been placed on locating and testing . host-specific natural enemies that feed on Tamarix It is hoped that this biological control program will ramosissima and T. parviflora. In Eurasia, insect AerialAerial photophoto graphsgraphs andand GIS are herbivores are known to exert extensive pressure on usefuluseful inin assessingassessing areasareas ofof infestation.infestation. help reduce saltcedar invasiveness and thus popula- Tamarix spp. and are thought to limit plant growth tions to below pest level status in the United States. and reproduction. Over 200 different herbivores We postulate that this reduction will allow native attack saltcedar in the areas where these plants are species to recover in many areas and thus benefit native. These native populations rarely reach pest Exotic and Invasive Weed Research Unit many other threatened and endangered species and status and never totally dominate riparian habitats. This rearch effort on Tamarix biology and control is an excellent example project where agriculture production. several groups are working cooperatively on one major problem area. Scientists, land managers and a number of other public and private groups have formed a Consortium to help develop and implement Tamarix biological control and revegetation efforts. Saltcedar, Tamarix spp., is an exotic shrub to small tree that has invaded approximately 1.2 million acres of riparian habitat across the western US from invasive and often out competes native species. California to the central Great Plains and from northern Mexico to Montana. It is estimated to have caused $16 billion in damage over the past 50 years. Currently, only a single insect species (an accidentally introduced leafhopper) is found in any significant

numbers feeding on saltcedar. In the USDA program, TheThe beetlesbeetles areare approvedapproved forfor releaserelease inin threethree CaliforniaCalifornia testtest sitessites .. approximately 30 different insect natural enemies are considered to be appropriate biological control agents.

TamarixTamarix damagedamage isis widespreadwidespread acrossacross thethe WesternWestern United States A single insect, the Tamarix leafbeetle (Diorhabda elongata) has been cleared for release by both the US Fish and Wildlife Service and the USDA Animal and Plant Health Inspection Service. Experimental cage Exotic and Invasive Weed Research Unit The first steps in our outdoor evaluations are tests conducted in large field cages. Studies of this releases are now underway in six western states. type have been completed in six western states in cooperation with the Saltcedar Consortium. The Consortium has just been funded for $3 million through a USDA grant that will allow this Exotic and Invasive Weed Research Unit research to be expanded to a larger scale and then implemented over extensive areas.

To date, beetles have been released into field cages In the United States, both T. ramosissima and T. in California, Colorado, Nevada, Texas, Utah and parviflora have shown invasive tendencies, Wyoming. In most of these sites, the beetles have often form monotypic stands, and cause DiorhabdaDiorhabda elongataelongata is the successfully survived the winter months and extensive damage through a variety of harmful firstfirst naturalnatural enemyenemy toto bebe introducedintroduced forfor saltcedarsaltcedar emerged in the spring of the year to cause major effects that damage many native plants and biologicalbiological control.control. defoliation of the test saltcedar plants. In test cages animals. Some of the invasive potential of in California, Colorado and Nevada, the beetles saltcedar is thought to be due to its better caused total defoliation of the saltcedar plants by adaptation to altered hydrological patterns and Classical biological control is the primary control method. Exotic and Invasive Weed Research Unit Exotic and Invasive Weed Research Unit mid summer. We are currently monitoring these other human controlled factors. However, the plants to determine their regrowth potential and Saltcedar originated in Eurasia from where it was introduced into the United States in the early 1800s. lack of herbivory has been suggested as one of To study its natural enemies, ARS scientists have cooperated with a large number of researchers in over loss of reproductive capacity. Additional research 10 different countries. Studies have identified over 200 insect natural enemies that feed on saltcedar in the most significant reasons that saltcedar is so its homeland. Several of those insects have been studied in detail and are now being permitted for re- continues on testing these and other agents that lease into the North American environment to help control this pest plant using biological control. may be released at some future date.

Tamarix parviflora and Arundo donax grow intermixed at one of our primary research The cage studies have shown that the Diorhabda elongata leaf beetles from China are able to sites near Davis, CA. The unit is currently attempting to address invasive weed issues QuarantineQuarantine testingtesting helpshelps toto ensureensure safety.safety. successfully establish in US conditions. In fact, in several of the release areas they increased and control them on a landscape scale using a combination of field, laboratory and Diorhabda elongata 10-25 fold in a single generation and caused complete defoliation of the caged saltcedar plants. Host-specificity No Choice Tests computer simulation/ GIS/ GPS technologies. 200 194.0 Research is now continuing within the cages to determine the long term impact on the Tamarix. Location of Eggs Laid Within Cages

On the Plant On Inert Substrates

100

54.0 Mean Number of Eggs Laid 120 TamarixTamarix grows with Giant Reed Owens Valley Open Cage Release 10.67 500 Adults100 Larvae 8.33 7.67 6.67 8.33 5.67 5.33 Released Adults 0.0 0 -- StudiesStudies onon plantplant growthgrowth andand Tamarix parviflora Tamarix aphylla Frankenia salina Frankenia palmeri Frankenia jamesii 80 Plant Species Tested

spreadspread inin agriculturalagricultural 60

Diorhabda elongata 40 areasareas areare underwayunderway Host-Specificity Choice Tests 60 Number of Individuals Counted on 12 Stems (ave length of 103 cm)

20 52.67

-- VegetativeVegetative reproductionreproduction isis 50

0 215 217 221 224 228 232 235 238 242 246 250 255 259 264 August 3 40 September 21 beingbeing studied.studied. Julian Date

30 29.0

Mean Number of Eggs Laid Field results have shown successful establishment and impact. 11.33 Field results have shown successful establishment and impact. 10 5.0

0.0 0.0 0.0 200 Eggs80 0 Released Tamarix parviflora Tamarix aphylla Frankenia salina Frankenia palmeri Frankenia jamesii Prunus dulicis Inert Substrate August 2, Owens Valley Sleeve Cages 1999 Plant Species Tested

60 Egg 1st 2nd 3rd -Biological control, Pupae -Biological control, Exotic and Invasive Weed Research Unit Beetles -Plant-Plant growthgrowth modeling,modeling, 40

-Remote-Remote sensingsensing andand 20

GISGIS/GPS use are being Detailed quarantine studies are conducted on insect natural enemies such as Individuals in Sleeve Cages 0 investigated.investigated. Diorhabda elongata, the first Tamarix natural enemy that has been approved by 210 220 230 240 250 260 270 USDA-APHIS and the US Fish and Wildlife Service for use against saltcedar. Julian Date Exotic and Invasive Weed Research Unit Exotic and Invasive Weed Research Unit