C. Jack DeLoach

Host specificity of the leaf beetle, Diorhabda elongata deserticola (Coleoptera: Chrysomelidae) from Asia, a biological control agent for saltcedars (Tamarix: Tamaricaceae) in the Western United States

Abstract Four species of saltcedars, Tamarix ramosissima Ledeb., Tamarix chinensis Lour., Tamarix parviflora DC., and T. canariensis Willd. and their hybrids, are exotic, invasive small trees from Asia that cause great damage to riparian ecosystems of the western United States. They displace native plant communities, degrade wildlife habitat (including that of many endangered species), increase soil salinity and wildfires, lower water tables, reduce water available for agriculture and municipalities, and reduce recreational use of affected areas. Phytophagous insects are abundant on saltcedar in the Old World and we selected Diorhabda elongata Brulle deserticola Chen as the top candidate biological control agent because of the great damage it causes, and its high host specificity, broad geographic range, and presumed adaptability in the United States. Literature review and our overseas surveys indicated that this insect is associated only with species of Tamarix and occasionally with Myricaria but not with Reumaria or Frankenia (all Tamaricales) in the Old World. In quarantine facilities in the United States, and overseas, we tested beetles from China and Kazakhstan on six species and three hybrids (26 accessions) of Tamarix and on 58 species of other plants, in 15 tests of different types, using 1852 adults and 3547 larvae, over 10 years. Survival from larvae to adults averaged 55–67% on the Tamarix species, 12% on Myricaria sp., and only 1.6% on the three Frankenia spp. No larvae completed their development on any of the other 54 plant species tested, where most larvae died during the first instar. Adults oviposited readily on T. ramosissima accessions, less on Tamarix aphylla (L.) Karst. (athel), and only rarely on other plants. The host range of the D. e. deserticola we tested from Kazakhstan was not different from those we tested from China. Therefore, D. e. deserticola , is sufficiently host-specific and was approved for field release in North America. This is the first biological control agent introduced into the United States for control of saltcedar.

Biology of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), an Asian leaf beetle for biological control of saltcedars (Tamarix spp.) in the United States

Adults and larvae of Diorhabda elongata Brullsubspecies deserticola Chen feed on the foliage of saltcedars (Tamarix spp.). All three instars are black, the 2nd with an indistinct, and the 3rd with a distinct yellowish lateral stripe; full-grown larvae reach ca. 9 mm in length and pupate in cells in litter on the ground or a few cm below the soil surface. Adults are yellowish with two dark brown stripes on each elytron. Duration of the egg averaged 5 days, 1st instar 4.9 days, 2nd instar 4.8 days, 3rd instar 7.4 days, prepupa 4.8 days, and pupa 7.1 days at 24.1C. Preoviposition averaged 3.9 days and an average female oviposited over a 12-day period and laid 194 eggs. Degree-day accumulations for development were 234.2 for the three larval instars and 91.3 for the pupa above a developmental threshold of 12.5C. Net reproductive rate (R0) in the laboratory at 28.6C and on the best Tamarix ac- cession was calculated at 88, generation time at 37 days, and innate capacity of increase (rm) at 0.112, giving a population doubling time of 6.2 days. In field cages in Colorado, Wyoming, Utah, Nevada, and California, overwintering adults emerged from late April to early May. Adults of the first generation emerged in early to mid-July, and 2nd generation adults emerged from mid-August to early September and overwintered. High populations of larvae developing in field cages caused defoliation, dieback, and sometimes death of the Tamarix trees. At the three study sites in Texas, maximum daylength was 14 h 21 min and larvae exposed to these conditions produced adults in reproductive diapause early in the season and subsequently failed to overwinter. North of 38 latitude in the United States, populations of D. e. deserticola originating from Fukang, China and Chilik, Kazakhstan are active throughout the growing season, successfully overwinter, and are potentially a highly effective control agent for saltcedar. Published by Elsevier Science (USA).

Saltcedar (Tamarix spp.), Endangered Species, and Biological Weed Control—Can They Mix?1

Abstract Saltcedar invasion has many economic and environmental effects, including displacement of native riparian vegetation and associated wildlife. A biological control program led to the approval in 1994 of two insects for introduction but was delayed by the presence of the endangered southwestern willow flycatcher (SWWF) in saltcedar. In 2001, the saltcedar leaf beetle was released in six states but not where the SWWF was present. Delays circumvent the benefits that saltcedar suppression could have for other declining species, including many rare or absent in ecosystems dominated by saltcedar. Numerous birds forage within saltcedar vegetation but in lower numbers and diversity than in native stands that provide better habitat and insect resources. Successful establishment by saltcedar leaf beetle resulted in extensive saltcedar defoliation, and observations of wildlife feeding on the beetles in an otherwise depauperate system suggest that biocontrol may enhance habitat quality for many species, including the SWWF. Consideration of the multiple species affected by saltcedar would have allowed more effective invasive plant management in this case, but delays also reflect drawbacks in federal administrative structures related to invasive species management in ‘natural areas’ as much as problems with a narrow focus on a single species. A functionally integrated approach where research and management decisions are made cooperatively would allow more rational management of invasive species in wildland ecosystems. Nomenclature: Saltcedar, Tamarix ramosissima Ledeb. #3 TAARA, complex also includes T. chinensis Lour. # TAACH, T. parviflora DC. # TAAPA; saltcedar leaf beetle, Diorhabda elongata; southwestern willow flycatcher, Empidonax traillii extimus Phillips. Additional index words: Biodiversity, ecological restoration, ecosystem management, riparian habitat. Abbreviations: APHIS, Animal and Plant Health Inspection Service; SWWF, southwestern willow flycatcher; USDA, U.S. Department of Agriculture; USFWS, U.S. Fish and Wildlife Service.

Assessment of risk to native Frankenia shrubs from an Asian leaf beetle, Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), introduced for biological control of saltcedars (Tamarix spp.) in the western United States.

Abstract Exotic saltcedars, Tamarix spp. (Tamaricaceae: Tamaricales) from Central Asia and the Mediterranean area, have invaded much of the western United States, where they degrade natural riparian areas, reduce water supplies, and interfere with agriculture and recreation. The major taxa are Tamarix ramosissima Ledeb., Tamarix chinensis Lour., and hybrids with these and Tamarix canariensis Willd. throughout much of the West, and Tamarix parviflora DC. in parts of California. The biology and host range of the leaf beetle, Diorhabda elongata Brulle subspecies deserticola Chen from Central Asia, indicate that it is a safe and potentially effective biological control agent. Here we report that species of the somewhat related native North American shrubs, Frankenia spp. (Frankeniaceae: Tamaricales), appear to be at little risk from the introduction of Diorhabda elongata deserticola. In laboratory, greenhouse, and outdoor cages at Temple, Texas and Albany, California, 0–27% of larvae were able to complete their development on four North American species of Frankenia compared to 53–56% on Tamarix host species, depending on the species tested and the growing conditions of the plants. However, adults were not attracted to, did not feed upon, and rarely laid eggs on Frankenia spp. Forced closer contact with Frankenia in smaller cages and even removing all Tamarix host plants did not increase adult selection of Frankenia plants nor oviposition on them. Adults from larvae reared on Frankenia did not show adaptation to nor increased utilization of the plant, compared to those reared on Tamarix. D. e. deserticola, therefore, appears sufficiently host-specific for field release in North America.

Establishment and Biological Success of Diorhabda elongata elongata1 on Invasive Tamarix in Texas

A leaf beetle, Diorhabda elongata elongata (Brullé), from Crete, Greece, was released unrestricted at two field locations (Lake Thomas and Beals Creek) within the upper Colorado River watershed of Texas between the summers of 2003 and 2004 as part of a Tamarix biological control program. D. elongata elongata released at the Lake Thomas site in August 2003 successfully overwintered and was recovered in the spring 2004; however, beetles were not recovered at Lake Thomas past June 2004 despite additional releases in July 2004. Following releases in April and July 2004 at Beals Creek, D. elongata elongata did establish and was subsequently recovered during 2005 and 2006. In August 2006, the D. elongata elongata population was dispersed throughout an area of approximately 12 hectares, beetles or larvae were present on 100% of the 47 trees surveyed and 57% of which (27 trees) were at least 90% defoliated by D. elongata elongata.

Field Evaluation of Diorhabda elongate and D. carinata (Coleoptera: Chrysomelidae) for Biological Control of Saltcedars (Tamarix spp.) in Northwest Texas

Abstract. Four species of Diorhabda (Coleoptera: Chrysomelidae) have been approved for release as biological control agents of invasive saltcedars (Tamarix spp.) in the U.S. Two species, D. elongata (Brullé) and D. carinata (Faldermann), were evaluated for their ability to establish populations in northwest Texas (from 32.5°N to 34.0°N) and increase in numbers sufficient to defoliate saltcedar trees. Following releases of adults during 2 years, D. elongata overwintered, established, and increased sufficiently to defoliate saltcedar trees at all three release sites. In contrast, D. carinata overwintered in the field at only one of three sites and then only in very low numbers. D. carinata did not defoliate saltcedar trees outside of cages at any release site. After 2 years of release efforts, D. carinata could not be detected at any of the three release sites during the third year and was not considered to have established. Survival of overwintering adult D. carinata was significantly greater than survival of overwintering D. elongata adults. However, D. carinata adults terminated overwintering quiescence earlier and were observed on saltcedar trees earlier in February and March than were D. elongata adults. These results suggested that emergence of adults from overwintering quiescence in late February and early March exposed D. carinata to freezing weather and contributed to the failure of the species to establish in northwest Texas. In contrast, D. elongata terminated overwintering quiescence latter and therefore experiences less risk of exposure to spring frost. These results suggested that D. elongata will be more effective than D. carinata for biological control of saltcedar in northwest Texas (32.5 to 34.0°N).