Northern tamarisk beetle
Northern tamarisk beetle
Diorhabda carinulata is a species of leaf beetle known as the northern tamarisk beetle, which feeds on tamarisk trees from southern Russia and Iran to Mongolia and western China. This beetle is used in North America as a biological pest control agent against saltcedar or tamarisk (Tamarix spp.), an invasive species in arid and semiarid ecosystems (where D. carinulata and its closely related sibling species are also less accurately referred to as the 'saltcedar beetle', 'saltcedar leaf beetle', 'salt cedar leaf beetle', or 'tamarisk leaf beetle').
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The northern tamarisk beetle was first described from southern Russia as Galeruca carinulata Desbrochers (1870). Weise (1893) created the genus Diorhabda and erroneously placed the northern tamarisk beetle as a junior synonym of a sibling species, the Mediterranean tamarisk beetle, Diorhabda elongata (Brullé). Chen (1961) described the species in western China as a new subspecies Diorhabda elongata deserticola Chen. Yu et al. (1996) proposed the species D. deserticola. Berti and Rapilly (1973) recognized the northern tamarisk beetle as a separate species Diorhabda carinulata (Desbrochers) based on detailed morphology of the endophallus of the male genitalia. Tracy and Robbins (2009) confirmed the findings of Berti and Rapilly (1973), established D. e. deserticola as a junior synonym to D. carinulata, and provided illustrated taxonomic keys separating the northern tamarisk beetle from the four other sibling species of the D. elongata (Brullé) species group: Diorhabda elongata, Diorhabda carinata (Faldermann), Diorhabda sublineata (Lucas), and Diorhabda meridionalis Berti and Rapilly. In literature prior to 2009, D. carinulata was usually referred to as D. elongata, a China/Kazakhstan ecotype of D. elongata (in the US), or D. elongata deserticola.
Extensive literature on the biology and host range of the northern tamarisk beetle in Kazakhstan, China, and Mongolia is found under the names D. elongata and D. e. deserticola. The northern tamarisk beetle is a well-known pest of tamarisk in western China, where in certain years large outbreaks of the beetle can defoliate thousands of acres of tamarisk trees. The species is controlled in western China to protect plantings of tamarisk for windbreaks and soil stabilization. In nature, the northern tamarisk beetle feeds on at least 14 species of tamarisk and the closely related genus Myricaria. All these food plants are restricted to the tamarisk plant family Tamaricaceae. Extensive laboratory host range studies verified it is a specialist feeder only on plants of the tamarisk family. In North America, it prefers T. ramosissima to T. parviflora in the field  and this preference is also seen in laboratory studies. In laboratory and field cage studies, the northern tamarisk beetle will also feed and complete development on Frankenia shrubs, distant relatives of tamarisks in the same plant order Caryophyllales which have species native to North America, but they greatly prefer to lay eggs upon tamarisk. Field studies in Nevada confirm the beetle will not significantly attack Frankenia (Dudley and Kazmer 2005).
The northern tamarisk beetle overwinters as adults on the ground in leaf litter beneath tamarisk trees. Adults become active and begin feeding and mating in the early spring when tamarisk leaves are budding. Eggs are laid on leaves, and hatch in about a week in warm weather. Three larval stages feed on tamarisk leaves for about two and a half weeks, when they crawl to the ground and spend about five days as a “C”-shaped inactive prepupa before pupating about one week. Adults emerge from pupae to complete the lifecycle in about 4–5 wk in the summer. (For images of various life stages, see Diorhabda carinulata at commons.) From two to four generations of tamarisk beetles occur through spring and fall in central Asia. In the late summer and early fall, adults begin to enter diapause in which they cease reproduction and feed to build fat bodies before seeking a protected place to overwinter beneath the tamarisk. Larvae and adults are sensitive to shorter day lengths as the summer progresses that signal the coming of winter and induce diapause. Cossé et al. (2005) identified an aggregation pheromone that adult male northern tamarisk beetles can emit to attract both males and females to certain tamarisk trees.
Biological control agent
The northern tamarisk beetle is currently the most successful biological control agent for tamarisk in North America. Populations taken from around 44°N latitude at Fukang, China, and Chilik, Kazakhstan, were initially released by the USDA Agricultural Research Service in 2001. Since its release, the insect has defoliated tens of thousands of acres of tamarisk in Nevada, Utah, Colorado, and Wyoming. However, it appears to be poorly adapted to some areas where other species of Old World tamarisk beetles are being introduced, such as the Mediterranean tamarisk beetle, Diorhabda elongata, in northern California and parts of West Texas, and the larger tamarisk beetle, Diorhabda carinata (Faldermann), and the subtropical tamarisk beetle, Diorhabda sublineata (Lucas), in parts of West Texas.
Tamarisk does not usually die from a single defoliation from tamarisk beetles, and it can resprout within several weeks of defoliation. Repeated defoliation of individual tamarisk trees can lead to severe dieback the next season and death of the tree within several years. Tamarisk beetle defoliation over the course of at least one to several years can severely reduce the nonstructural carbohydrate reserves in the root crowns of tamarisk. Biological control of tamarisk by the northern tamarisk beetle will not eradicate tamarisk, but it has the potential to suppress by 75–85%, after which both northern tamarisk beetle and tamarisk populations should reach equilibrium at lower levels.
A primary objective of tamarisk biological control with the northern tamarisk beetle is to reduce competition by exotic tamarisk with a variety of native riparian flora, including trees (willows, cottonwoods, and honey mesquite), shrubs (wolfberry, saltbush, and baccharis), and grasses (alkali sacaton, saltgrass, and creeping and basin wildryes). Unlike expensive chemical and mechanical controls of tamarisk that often must be repeated, biological control does not harm native flora and is self-sustaining in the environment. Recovery of native riparian grasses can be quite rapid under the once-closed canopy of repeatedly defoliated tamarisk. However, beetle defoliation can locally reduce nesting habitat for riparian woodland birds until the native woodland flora is able to return. In some areas, tamarisk may be replaced by grasslands or shrublands, resulting in losses of riparian forest habitats for birds. Releases of tamarisk beetles in southern California, Arizona, and along the Rio Grande in western New Mexico, are currently delayed until concerns can be resolved regarding safety of tamarisk biological control to nesting habitats of the federally endangered southwestern willow flycatcher (Empidonax traillii extimus), which will nest in tamarisk. The northern tamarisk beetle has defoliated some tamarisk nest trees of the southwestern willow flycatcher on the Virgin River in southern Utah, and actions to protect the flycatcher are under consideration. In 2010, the USDA Animal and Plant Health Inspection Service (APHIS) officially discontinued its program for release of the beetle in 13 northwestern states  over concern for the flycatcher. The Colorado Department of Agriculture is continuing to redistribute beetles within their state, and they are seeing vigorous growth of native vegetation such as willows in response to reductions in tamarisk by the northern tamarisk beetle.
- Bean, D.W.; Dudley, T.L.; Keller, J.C. 2007a: Seasonal timing of diapause limits the effective range of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae) as a biological control agent for tamarisk (Tamarix spp.). Environmental Entomology, 36(1): 15–25. PDF
- Bean, D.W.; Wang, T.; Bartelt, R.J.; Zilkowski, B.W. 2007b: Diapause in the leaf beetle Diorhabda elongata (Coleoptera: Chrysomelidae), a biological control agent for tamarisk (Tamarix spp.). Environmental Entomology, 36(3): 531–540. PDF
- Berti, N.; Rapilly, M. 1973: Contribution a la faune de l’Iran; Voyages de MM. R. Naviaux et M. Rapilly (Col. Chrysomelidae). Annales de la Société Entomologique de France, 9(4): 861–894. (In French)
- Chen, S.H. 1961: New Species of Chinese Chrysomelidae. Acta Entomologica Sinica, 10(4–6): 429–435. (In Chinese with English summary)
- Cossé, A.A.; Bartelt, R.J.; Zilkowski, B.W.; Bean, D.W.; Petroski, R.J. 2005: The aggregation pheromone of Diorhabda elongata, a biological control agent of saltcedar (Tamarix sp.): Identification of two behaviorally active components. Journal of Chemical Ecology, 31(3): 657–670. PDF
- Dalin, P.; O'Neal, M.J.; Dudley, T.; Bean, D.W.; 2009: Host plant quality of Tamarix ramosissima and T. parviflora for three sibling species of the biocontrol insect Diorhabda elongata (Coleoptera: Chrysomelidae). Environmental Entomology, 38(5): 1373–1378. PDF
- DeLoach, C.J.; Lewis, P.A.; Herr, J.C.; Carruthers, R.I.; Tracy, J.L.; Johnson, J. 2003: 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. Biological Control, 27: 117–147. PDF
- DeLoach, C.J.; Carruthers, R. 2004: Biological control programs for integrated invasive plant management. In: Proceedings of Weed Science Society of America Meeting, Kansas City, MO. Weed Science Society of America (CD-ROM). 17 pp. PDF
- DeLoach, C.J.; Carruthers, R.I.; Lovich, J.E.; Dudley, T.L.; Smith, S.D. 2000: Ecological interactions in the biological control of saltcedar (Tamarix spp.) in the United States: toward a new understanding. In: N. R. Spencer (ed.), Proceedings of the X International Symposium on Biological Control of Weeds, 4–14 July 1999, Montana State University. Bozeman, Montana, pp. 819–873. PDF
- Desbrochers des Loges, M.J. 1870: Descriptions de Coléoptères nouveaux d’Europe et confins. L’Abeille, Volume 7, Part 1: 10–135. (In French)
- Dudley, T.L. DeLoach, C.J. 2004: Saltcedar (Tamarix spp.), endangered species, and biological weed control-can they mix? Weed Technology, 18(5): 1542–1551. PDF
- Dudley, T.L.; Kazmer, D.J. 2005: Field assessment of the risk posed by Diorhabda elongata, a biocontrol agent for control of saltcedar (Tamarix spp.), to a nontarget plant, Frankenia salina. Biological Control, 35: 265–275. PDF
- Dudley, T. L.; Dalin, P.; Bean, D.W 2006: Status of biological control of Tamarix spp. in California. In: M. S. Hoddle and M. W. Johnson (eds.), Proceedings of the Fifth California Conference on Biological Control, 25–26 July 2006, Riverside, CA. University of California at Riverside, Riverside, California, pp. 137–140. PDF
- Gruver, M. 2010: USDA stops using beetles vs. invasive saltcedar. Associated Press, 21 June 2010. 
- Hudgeons, J.L.; Knutson, A.E.; Heinz, K.M.; DeLoach, C.J.; Dudley, T.L.; Pattison, R.R.; Kiniry, J.R. 2007: Defoliation by introduced Diorhabda elongata leaf beetles (Coleoptera: Chrysomelidae) reduces carbohydrate reserves and regrowth of Tamarix (Tamaricaceae). Biological Control, 43: 213–221. PDF
- Johnson, K. 2010: In battle of bug vs. shrub, score one for the bird. New York Times, 22 June 2010. 
- Lewis, P.A.; DeLoach, C.J; Herr, J.C.; Dudley, T.L.; Carruthers, R.I. 2003a: 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. Biological Control, 27: 148–166. PDF
- Lewis, P.A.; DeLoach, C.J.; Knutson, A.E.; Tracy, J.L.; Robbins, T.O. 2003b: Biology of Diorhabda elongata deserticola (Coleoptera: Chrysomelidae), an Asian leaf beetle for biological control of saltcedars (Tamarix spp.) in the United States. Biological Control, 27: 101–116. PDF
- Milbrath, L.; DeLoach, C.J. 2006: Host specificity of different populations of the leaf beetle Diorhabda elongata (Coleoptera: Chrysomelidae), a biological control agent of saltcedar (Tamarix spp.). Biological Control, 36: 32–48. PDF
- Tracy, J.L.; DeLoach, C.J. 1999: Biological control of saltcedar in the United States: Progress and projected ecological effects. In: Bell, C.E. (Ed.), Arundo and Saltcedar: The Deadly Duo, Proceedings of the Arundo and Saltcedar Workshop, 17 June 1998. Ontario, California, 111–154. PDF
- Tracy, J.L.; Robbins, T.O. 2009: Taxonomic revision and biogeography of the Tamarix-feeding Diorhabda elongata (Brullé, 1832) species group (Coleoptera: Chrysomelidae: Galerucinae: Galerucini) and analysis of their potential in biological control of Tamarisk. Zootaxa, 2101: 1-152. PDF
- Yu, P.; Wang, S.; Yang, X. 1996: Economic Insect Fauna of China, Fasc. 54, Coleoptera: Chrysomeloidea (II). Science Press, Beijing, China, 324 pp. (In Chinese)
- Weise, J. 1893: Chrysomelidae. In: Erichson, W. (ED.), Naturgeschichte der Insecten Deutschland, 61(73): 961–1161. (In German)
- USDA APHIS. 2005: Program for Biological Control of Saltcedar (Tamarix spp.) in Thirteen States: Environmental Assessment. USDA APHIS, Fort Collins, Colorado. 56 pp. PDF
- Tracy and Robbins (2009) provide a detailed review of the distribution, biogeography, biology, and taxonomy of D. carinulata that is a general source for most of this article.
- (Tracy and Robbins 2009).
- (Dudley et al. 2006)
- (Dalin et al. 2009)
- (DeLoach et al. 2003, Lewis et al. 2003a, Milbrath and DeLoach 2006).
- (Lewis et al. 2003b).
- (Bean et al. 2007a, 2007b).
- (DeLoach and Carruthers 2004).
- (Hudgeons et al. 2007).
- DeLoach and Carruthers 2004, Tracy and DeLoach 1999
- (Tracy and DeLoach 1999).
- (see DeLoach et al. 2000, Dudley and DeLoach 2004).
- See link to Center for Biological Diversity 17 June 2009 press release below.
- USDA APHIS 2005)
- (Gruver 2010).
- (Johnson 2010).
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- Center for Biological Diversity 17 June 2009 press release regarding lawsuit to protect the southwestern willow flycatcher in view of defoliation of tamarisk nesting habitat by D. carinulata. 
- Montana War on Weeds information on D. carinulata (not D. elongata) for tamarisk biocontrol. 
- Tamarisk Coalition information on tamarisk biocontrol (China and Kazakhstan source tamarisk beetles are D. carinulata).
- University of California Berkeley Campus News article on initial 2001 release of D. carinulata (not D. elongata). 
- USDA/ARS research with D. carinulata (not D. elongata) for tamarisk biocontrol in Wyoming and Montana. 
- USDA/ARS and Texas Agri-Life Research and Extension Service Report of Information to the Public; Progress on Biological Control of Saltcedar in the Western U.S.: Emphasis—Texas 2004-2009. PDF