Diorhabda Carinulata Research Articles

Tamarisk biocontrol, endangered species risk and resolution of conflict through riparian restoration

A long-standing debate between wildlife agencies and biological control researchers and practitioners concerns Diorhabda carinulata Desbrochers (Coleoptera: Chrysomelidae) introduced to suppress invasive Tamarix spp. (Tamaricaceae), and potential impacts of Tamarix defoliation on endangered southwestern willow flycatchers using this non-native plant as nesting habitat in some western riparian ecosystems. The conflict and ensuing legal actions are currently centered on the presence of D. carinulata within the breeding range of the flycatcher in the Virgin River watershed, which has led to APHIS termination of permits supporting the biocontrol development program and has also affected other programs to develop biocontrol agents against environmental weeds. Central to concerns over wildlife is the lack of rehabilitation of native vegetation where biocontrol is expected, so there are current and planned efforts to promote restoration of native cottonwood-willow habitat to mitigate the anticipation decline in Tamarix cover. A strategic approach to riparian restoration is outlined which could facilitate sustainable, and scientifically documented recovery of this iconic habitat type. While the results of these efforts will not be known immediately, the process which is leading to riparian restoration has brought specialists from both sides of the debate together in search of resolution via collaboration, and if successful, may allow re-initiation of the Tamarix biocontrol program attendant with habitat enhancement for wildlife species of conservation concern.

Regional scale impacts of Tamarix leaf beetles (Diorhabda carinulata) on the water availability of western U.S. rivers as determined by multi-scale remote sensing methods

Tamarix leaf beetles (Diorhabda carinulata) have been widely released on western U.S. rivers to control introduced shrubs in the genus Tamarix. Part of the motivation to control Tamarix is to salvage water for human use. Information is needed on the impact of beetles on Tamarix seasonal leaf production and subsequent water use over wide areas and multiple cycles of annual defoliation. Here we combine ground data with high resolution phenocam imagery and moderate resolution (Landsat) and coarser resolution (MODIS) satellite imagery to test the effects of beetles on Tamarix evapotranspiration (ET) and leaf phenology at sites on six western rivers. Satellite imagery covered the period 2000 to 2010 which encompassed years before and after beetle release at each study site. Phenocam images showed that beetles reduced green leaf cover of individual canopies by about 30% during a 6–8week period in summer, but plants produced new leaves after beetles became dormant in August, and over three years no net reduction in peak summer leaf production was noted. ET was estimated by vegetation index methods, and both Landsat and MODIS analyses showed that beetles reduced ET markedly in the first year of defoliation, but ET recovered in subsequent years. Over all six sites, ET decreased by 14% to 15% by Landsat and MODIS estimates, respectively. However, results were variable among sites, ranging from no apparent effect on ET to substantial reduction in ET. Baseline ET rates before defoliation were low, 394mmyr−1 by Landsat and 314mmyr−1 by MODIS estimates (20–25% of potential ET), further constraining the amount of water that could be salvaged. Beetle–Tamarix interactions are in their early stage of development on this continent and it is too soon to predict the eventual extent to which Tamarix populations will be reduced. The utility of remote sensing methods for monitoring defoliation was constrained by the small area covered by each phenocam image, the low temporal resolution of Landsat, and the low spatial resolution of MODIS imagery. Even combined image sets did not adequately reveal the details of the defoliation process, and remote sensing data should be combined with ground observations to develop operational monitoring protocols.

Retention of immunolabels by Diorhabda carinulata, a biological control agent of saltcedar

AbstractMarking biological control agents facilitates studies of dispersal and predation. This study examines the feasibility of marking the various life stages of a weed biological control agent, Diorhabda carinulata (Desbrochers) (Coleoptera: Chrysomelidae), by submersion in rabbit or chicken immunoglobulin G (IgG) protein solutions. We determined whether externally applied IgGs are effective labels of the various lifestages, whether IgGs can be retained between D. carinulata lifestages, and to what extent abiotic factors associated with field conditions mediate label retention. The presence of the labels on the various lifestages of the beetles was detected by IgG‐specific enzyme‐linked immunosorbent assays. Duration of each immunolabel was measured on eggs and larvae in laboratory studies and on adults in laboratory and field studies. For adults, both labels showed high (>80%) retention for ca. 14 days after marking under field and laboratory conditions. Temperature and type of label (rabbit or chicken) had only a minimal effect on marker retention. Externally marked eggs exhibited high (100%) retention for both proteins over the entire duration of the egg stage. Interestingly, some larvae emerging from externally labeled eggs contained both external and internal IgG marks. To our knowledge, this is the first case of an IgG being transferred from the egg to larva of an insect. Age of eggs at the time of label application affected the intensity of the external label on neonates. For instance, larvae that emerged from eggs that were >1 day old when labeled exhibited stronger label retention than larvae that emerged from eggs that were 1 day old when labeled. For larvae, retention of rabbit IgG was greater than retention of chicken IgG. Label retention declined as larvae aged; larvae >3 days old retained significantly less label than did neonate larvae. Both IgG labels were retained from the first to second instar, but at a very low rate of <10%. Overall, our study demonstrates that protein‐marking technology has potential for use in studies of dispersal and predator–prey associations for D. carinulata.

Converting Riparian Restoration Waste to Energy: Testing Tamarisk (Tamarix spp.) Woody Biomass as Fuel for Downdraft Gasification

Jamie Nielsen, James Diebold, Tillie Walton, Michael Boyle and Robb Walt

Multiple-level defoliation assessment with hyperspectral data: integration of continuum-removed absorptions and red edges

Hyperspectral data were collected from 40 canopies of saltcedar (Tamarix ramosissima): 10 healthy canopies and 30 canopies defoliated by an introduced biological control agent, the saltcedar leaf beetle (Diorhabda carinata). These data assessed multiple-level defoliations in response to the process of biological control. Two important characteristics of the hyperspectral data – red edges and continuum-removed absorptions – were used to discriminate four defoliation categories of saltcedar (healthy plants, newly defoliated plants, completely defoliated plants and refoliating plants) at the canopy level. The red edge positions were located at ranges of 711–716 nm, 706–712 nm, 694–698 nm and 715–719 nm for the four defoliation stages described above, respectively. These red edge positions alone could not clearly judge the four defoliation categories associated with feeding by the beetles. Only the completely defoliated canopies had distinct red edge positions that could be differentiated from the other three types of canopies. While using a classification tree to integrate the red edge positions and their derivatives with the central band depths of these five continuum-removed absorptions, it was found that only two band depths of the continuum-removed absorptions were selected, which were the red absorption between 570 and 716 nm and the water absorption between 936 and 990 nm in the near-infrared region (NIR). This implied that the continuum-removed absorptions outperformed the red edges for identifying the defoliation categories. The resulting overall accuracy was 87.5%. The producer accuracy was 100%, 70%, 100% and 80% for the healthy plants, newly defoliated, completely defoliated plants and refoliating canopies, respectively. The corresponding user accuracy was 90.91%, 77.78%, 100% and 80%. Therefore, we concluded that single spectral data based variable failed to separate the four stages but a combination of the two continuum-removed absorptions located in the blue absorption and the first water absorption in the NIR improved the identification of defoliated canopies associated with the dynamic defoliation process of the biological control agent. This study developed the defoliation detection techniques of commonly used binary levels (i.e. defoliation and non-defoliation) to multiple vegetation defoliation levels. We anticipate applying these assessment techniques to wide-area collections of hyperspectral data covering the two spectral regions as described above to further evaluate the effectiveness of these biological control beetles and their impact on saltcedar management in the Western United States.

Tamarisk Biocontrol Using Tamarisk Beetles: Potential Consequences For Riparian Birds in the Southwestern United States

Abstract. The tamarisk beetle (Diorhabda spp.), a non-native biocontrol agent, has been introduced to eradicate tamarisk (Tamarix spp.), a genus of non-native tree that has become a dominant component of riparian woodlands in the southwestern United States. Tamarisk beetles have the potential to spread widely and defoliate large expanses of tamarisk habitat, but the effects of such a widespread loss of riparian vegetation on birds remains unknown. We reviewed literature on the effects of other defoliating insects on birds to investigate the potential for tamarisk beetles to affect birds positively or negatively by changing food abundance and vegetation structure. We then combined data on the temporal patterns of tamarisk defoliation by beetles with nest productivity of a well-studied riparian obligate, the Southwestern Willow Flycatcher (Empidonax traillii extimus), to simulate the potential demographic consequences of beetle defoliation on breeding riparian birds in both the short and long term. Our resu...

A habitat overlap analysis derived from maxent for tamarisk and the south-western willow flycatcher

Biologic control of the introduced and invasive, woody plant tamarisk (Tamarix spp, saltcedar) in south-western states is controversial because it affects habitat of the federally endangered South-western Willow Flycatcher (Empidonax traillii extimus). These songbirds sometimes nest in tamarisk where floodplain-level invasion replaces native habitats. Biologic control, with the saltcedar leaf beetle (Diorhabda elongate), began along the Virgin River, Utah, in 2006, enhancing the need for comprehensive understanding of the tamarisk-flycatcher relationship. We used maximum entropy (Maxent) modeling to separately quantify the current extent of dense tamarisk habitat (>50% cover) and the potential extent of habitat available for E. traillii extimus within the studied watersheds. We used transformations of 2008 Landsat Thematic Mapper images and a digital elevation model as environmental input variables. Maxent models performed well for the flycatcher and tamarisk with Area Under the ROC Curve (AUC) values of 0.960 and 0.982, respectively. Classification of thresholds and comparison of the two Maxent outputs indicated moderate spatial overlap between predicted suitable habitat for E. traillii extimus and predicted locations with dense tamarisk stands, where flycatcher habitat will potentially change flycatcher habitats. Dense tamarisk habitat comprised 500 km2 within the study area, of which 11.4% was also modeled as potential habitat for E. traillii extimus. Potential habitat modeled for the flycatcher constituted 190 km2, of which 30.7% also contained dense tamarisk habitat. Results showed that both native vegetation and dense tamarisk habitats exist in the study area and that most tamarisk infestations do not contain characteristics that satisfy the habitat requirements of E. traillii extimus. Based on this study, effective biologic control of Tamarix spp. may, in the short term, reduce suitable habitat available to E. traillii extimus, but also has the potential in the long term to increase suitable habitat if appropriate mixes of native woody vegetation replace tamarisk in biocontrol areas.

UVB exposure does not accelerate rates of litter decomposition in a semi-arid riparian ecosystem

Abstract Aboveground litter decomposition is controlled mainly by substrate quality and climate factors across terrestrial ecosystems, but photodegradation from exposure to high-intensity ultraviolet-B (UVB) radiation may also be important in arid and semi-arid environments. We investigated the interactive effects of UVB exposure and litter quality on decomposition in a Tamarix -invaded riparian ecosystem during the establishment of an insect biological control agent in northern Nevada. Feeding by the northern tamarisk beetle ( Diorhabda carinulata ) on Tamarix spp. trees leads to altered leaf litter quality and increased exposure to solar UVB radiation from canopy opening. In addition, we examined the dynamics of litter decomposition of the invasive exotic Lepidium latifolium , because it is well-situated to invade beetle-infested Tamarix sites. Three leaf litter types (natural Tamarix , beetle-affected Tamarix , and L. latifolium ) differing in substrate quality were decomposed in litterbags for one year in the field. Litterbags were subjected to one of three treatments: (1) Ambient UVB or (2) Reduced UVB (where UVB was manipulated by using clear plastic films that transmit or block UVB), and (3) No Cover (a control used to test for the effect of using the plastic films, i.e. a cover effect). Results showed a large cover effect on rates of decomposition and nutrient release, and our findings suggested that frequent cycles of freeze–thaw, and possibly rainfall intensity, influenced decomposition at this site. Contrary to our expectations, greater UVB exposure did not result in faster rates of decomposition. Greater UVB exposure resulted in decreased rates of decomposition and P release for the lower quality litter and no change in rates of decomposition and nutrient release for the two higher quality litter types, possibly due to a negative effect of UVB on soil microbes. Among litter types, rates of decomposition and net release of N and P followed this ranking: L. latifolium > beetle-affected Tamarix > natural Tamarix . Altered nutrient dynamics with beetle introduction as well as the rapid decomposition rates exhibited by L. latifolium are consistent with vulnerability to secondary invasion. In this desert ecosystem, decomposition and nutrient release were strongly affected by litter type and much less so by UVB exposure.

Influence of Nutrient Levels inTamarixonDiorhabda sublineata(Coleoptera: Chrysomelidae) Survival and Fitness With Implications for Biological Control

Establishment of the saltcedar leaf beetle (Diorhabda spp.) has been unpredictable when caged or released in the field for saltcedar (Tamarix spp.) biocontrol. It has been observed that one caged tree might be voraciously fed upon by beetles while an adjacent tree in the cage is left untouched. We hypothesized that differences in the nutrient content of individual trees may explain this behavior. We evaluated survival, development rate, and egg production of beetles fed in the laboratory on saltcedar foliage from trees that had been grown under a range of fertilizer treatments. Tissue samples from the experimental trees and from the field were analyzed for percent nitrogen, phosphorus, and potassium. There was essentially no survival of beetle larvae fed foliage from saltcedar trees at nitrogen levels below 2.0%. At levels above 2.0% N, beetle larvae had corresponding increased survival rates and shorter development times. Multiple regression analyses indicated that nitrogen and phosphorus are important for larval survival and faster development rates. Higher levels of potassium were important for increased egg cluster production. The plant tissue analysis showed that the percentage of nitrogen in the experimental trees reflected the range of trees in the field and also that there is high variability within trees in the field. Our research indicates that if beetles are released on trees with poor nutrient quality, the larvae will not survive.

Biological control reduces growth, and alters water relations of the saltcedar tree (Tamarix spp.) in western Nevada, USA

We monitored the impacts of a biological control agent, the saltcedar leaf beetle (Diorhabda carinulata), on the saltcedar tree (Tamarix spp.) at two sites (Humboldt and Walker rivers) in Nevada, USA. At the Humboldt site trees that had experienced three to four defoliation events had more negative water potentials and lower foliar Δ13C than trees farther from the release site that had experienced only one defoliation event. We established paired trees (exposed to D. carinulata and sprayed with insecticide) at both sites and monitored impacts. Beetles reduced stem growth during the first year of defoliation at both sites but not in the second year at the Humboldt site. Defoliation did not affect midday water potentials, or leaf gas exchange during the first two years of defoliation of paired trees at either site. Furthermore there was no difference in foliar Δ13C in either year at the Humboldt site but defoliation during the first year lead to higher foliar Δ13C at the Walker site. These results suggest that initial defoliation by D. carinulata reduces growth but not water relations of saltcedar. However, repeated defoliation, potentially acting through reduced root growth, leads to an overall reduction in the water status of this invader.

Early impacts of biological control on canopy cover and water use of the invasive saltcedar tree (Tamarix spp.) in western Nevada, USA

The success of biological control programs is rarely assessed beyond population level impacts on the target organism. The question of whether a biological control agent can either partially or completely restore ecosystem services independent of population level control is therefore still open to discussion. Using observational and experimental approaches, we investigated the ability of the saltcedar leaf beetle [Diorhabda carinulata (Brullé) (Coleoptera: Chrysomelidae)] to reduce the water use of saltcedar trees (Tamarix ramosissima Ledeb.) in two sites (Humboldt and Walker Rivers) in Nevada, USA. At these sites D. carinulata defoliated the majority of trees within 25 and 9 km, respectively, of the release location within 3 years. At the Humboldt site, D. carinulata reduced the canopy cover of trees adjacent to the release location by >90%. At a location 4 km away during the first year of defoliation, D. carinulata reduced peak (August) stem water use by 50-70% and stand transpiration (July to late September) by 75% (P = 0.052). There was, however, no reduction in stem water use and stand transpiration during the second year of defoliation due to reduced beetle abundances at that location. At the Walker site, we measured stand evapotranspiration (ET) in the center of a large saltcedar stand and found that ET was highest immediately prior to D. carinulata arrival, dropped dramatically with defoliation, and remained low through the subsequent 2 years of the study. In contrast, near the perimeter of the stand, D. carinulata did not reduce sap flow, partly because of low rates of defoliation but also because of increased water use per unit leaf area in response to defoliation. Taken together, our results provide evidence that in the early stages of population expansion D. carinulata can lead to substantial declines in saltcedar water use. The extent of these declines varies spatially and temporally and is dependent on saltcedar compensatory responses along with D. carinulata population dynamics and patterns of dispersal.

A River System to Watch: Documenting the Effects of Saltcedar (Tamarix spp.) Biocontrol in the Virgin River Valley

spp.) can form dense, mono-typic stands and is often reported to have detrimental effects on native plants and habitat quality (Everitt 1980; Shafroth et al. 2005). Natural resource managers of these riparian areas spend considerable time and resources con-trolling saltcedar using a variety of techniques, including chemical (Duncan and McDaniel 1998), mechanical, and burning methods (Shafroth et al. 2005). Approximately one billion dollars are spent each year on river restoration projects nationally (Bernhardt et al. 2005), and a majority of these projects focus on invasive species control in the Southwest (Follstad Shah et al. 2007).A technique that has drawn much attention is the use of the saltcedar leaf beetle (

Insect biological control accelerates leaf litter decomposition and alters short‐term nutrient dynamics in aTamarix‐invaded riparian ecosystem

Insect herbivory can strongly influence ecosystem nutrient dynamics, yet the indirect effects of herbivore‐altered litter quality on subsequent decomposition remain poorly understood. The northern tamarisk beetleDiorhabda carinulatawas released across several western states as a biological control agent to reduce the extent of the invasive treeTamarixspp. in highly‐valued riparian ecosystems; however, very little is currently known about the effects of this biocontrol effort on ecosystem nutrient cycling. In this study, we examined alterations to nutrient dynamics resulting from beetle herbivory in aTamarix‐invaded riparian ecosystem in the Great Basin Desert in northern Nevada, USA, by measuring changes in litter quality and decomposition, as well as changes in litter quantity. Generally, herbivory resulted in improved leaf litter chemical quality, including significantly increased nitrogen (N) and phosphorus (P) concentrations and decreased carbon (C) to nitrogen (C:N), C:P, N:P, and lignin:N ratios. Beetle‐affected litter decomposed 23% faster than control litter, and released 16% more N and 60% more P during six months of decomposition, as compared to control litter. Both litter types showed a net release of N and P during decomposition. In addition, herbivory resulted in significant increases in annual rates of total aboveground litter and leaf litter production of 82% and 71%, respectively, under theTamarixcanopy. Our finding that increased rates of N and P release linked with an increased rate of mass loss during decomposition resulting from herbivore‐induced increases in litter quality provides new support to the nutrient acceleration hypothesis. Moreover, results of this study demonstrate that the introduction of the northern tamarisk beetle as biological control to aTamarix‐invaded riparian ecosystem has lead to short‐term stimulation of nutrient cycling. Alterations to nutrient dynamics could have implications for future plant community composition, and thus the potential for restoration ofTamarix‐invaded ecosystems.

Seasonal Adaptations to Day Length in Ecotypes ofDiorhabdaspp. (Coleoptera: Chrysomelidae) Inform Selection of Agents Against Saltcedars (Tamarixspp.)

Seasonal adaptations to daylength often limit the effective range of insects used in biological control of weeds. The leaf beetle Diorhabda carinulata (Desbrochers) was introduced into North America from Fukang, China (latitude 44° N) to control saltcedars (Tamarix spp.), but failed to establish south of 38° N latitude because of a mismatched critical daylength response for diapause induction. The daylength response caused beetles to enter diapause too early in the season to survive the duration of winter at southern latitudes. Using climate chambers, we characterized the critical daylength response for diapause induction (CDL) in three ecotypes of Diorhabda beetles originating from 36, 38, and 43° N latitudes in Eurasia. In a field experiment, the timing of reproductive diapause and voltinism were compared among ecotypes by rearing the insects on plants in the field. CDL declined with latitude of origin among Diorhabda ecotypes. Moreover, CDL in southern (<39° N latitude) ecotypes was shortened by more than an hour when the insects were reared under a fluctuating 35-15°C thermoperiod than at a constant 25°C. In the northern (>42° N latitude) ecotypes, however, CDL was relatively insensitive to temperature. The southern ecotypes produced up to four generations when reared on plants in the field at sites south of 38° N, whereas northern ecotypes produced only one or two generations. The study reveals latitudinal variation in how Diorhabda ecotypes respond to daylength for diapause induction and how these responses affect insect voltinism across the introduced range.

Sap flux-scaled transpiration by tamarisk ( Tamarix spp.) before, during and after episodic defoliation by the saltcedar leaf beetle ( Diorhabda carinulata)

The release of the saltcedar beetle ( Diorhabda carinulata) has resulted in the periodic defoliation of tamarisk ( Tamarix spp.) along more than 1000 river km in the upper Colorado River Basin and is expected to spread along many other river reaches throughout the upper basin, and possibly into the lower Colorado River Basin. Identifying the impacts of these release programs on tamarisk water use and subsequent water cycling in arid riparian systems are largely unknown, due in part to the difficulty of measuring water fluxes in these systems. We used lab-calibrated, modified heat-dissipation sap flux sensors to monitor tamarisk water use ( n = 20 trees) before, during and after defoliation by the saltcedar leaf beetle during the 2008 and 2009 growing seasons (May–October) in southeastern Utah. We incorporated a simple model that related mean stem sap flux density ( J s) with atmospheric vapor pressure deficit ( vpd) before the onset of defoliation in 2008. The model was used to calculate differences between predicted J s and J s measured throughout the two growing seasons. Episodic defoliation resulted in a 16% reduction in mean annual rates of J s in both 2008 and 2009, with decreases occurring only during the periods in which the trees were defoliated (about 6–8 weeks per growing season). In other words, rates of J s rebounded to values predicted by the model when the trees produced new leaves after defoliation. Sap flux data were scaled to stand water use by constructing a tamarisk-specific allometric equation to relate conducting sapwood area to stem diameter, and by measuring the size distribution of stems within the stand. Total water use in both years was 0.224 m, representing a reduction of about 0.04 m yr −1. Results showed that repeated defoliation/refoliation cycles did not result in a progressive decrease in either leaf production or water use over the duration of the study. This investigation improves ground-based estimates of tamarisk water use, and will support future efforts to characterize impacts of the beetle on basin-wide hydrologic processes.

Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabda carinulata Desbrochers) in a controlled environment

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf drop appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.

Lack of Establishment of the Mediterranean Tamarisk Beetle Diorhabda elongate (Coleoptera: Chrysomelidae) on Athel (Tamarix aphylla) (Tamaricaceae) in South Texas1

Adult Mediterranean tamarisk beetles, Diorhabda elongate (Brullé), a defoliator of exotic saltcedar (Tamarix spp.), were released into four field cages containing small saltcedar trees or closely-related exotic athel trees (Tamarix aphylla (L.) Karsten) and onto uncaged beneficial mature athel trees at sites in south Texas. In field cages, egg, larval, and adult densities per meter of green foliage were equal on saltcedar and athel in the first 8 weeks after release, but numbers of eggs, larvae, and adults were at least two-fold more on saltcedar. During this time, the beetles reduced green foliage by 50% on athel and by 20% on saltcedar. However, athel green foliage recovered after 10 weeks, while saltcedar foliage continued to decline. At two roadside field sites containing mature athel and no saltcedar, D. elongata adults were released in bagged athel branches in July 2006 and May 2007 and produced larvae that defoliated the branches by the third week after infestation. A few larvae and adults were found on unbagged athel branches during the first 3 months after release, but beetles failed to become established on athel trees and removed no more than 3% of green foliage from athel branches, which remained >85% green for 2 years. The Mediterranean tamarisk beetle thus did not colonize or cause permanent disfiguring damage to athel trees.

Tamarisk biocontrol in the western United States: ecological and societal implications

Tamarisk species (genus Tamarix), also commonly known as saltcedar, are among the most successful plant invaders in the western United States. At the same time, tamarisk has been cited as having enormous economic costs. Accordingly, local, state, and federal agencies have undertaken considerable efforts to eradicate this invasive plant and restore riparian habitats to pre‐invasion status. Traditional eradication methods, including herbicide treatments, are now considered undesirable, because they are costly and often have unintended negative impacts on native species. A new biological control agent, the saltcedar leaf beetle (Diorhabda elongata), has been released along many watersheds in the western US, to reduce the extent of tamarisk cover in riparian areas. However, the use of this insect as a biological control agent may have unintended ecological, hydrological, and socioeconomic consequences that need to be anticipated by land managers and stakeholders undertaking restoration efforts. Here, we examine the possible ramifications of tamarisk control and offer recommendations to reduce potential negative impacts on valued riparian systems in the western US.

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

The primarily Palearctic Diorhabda elongata species group is established for five Tamarix-feeding sibling species(tamarisk beetles): D. elongata (Brullé, 1832), D. carinata (Faldermann, 1837), D. sublineata (Lucas, 1849) REVISEDSTATUS, D. carinulata (Desbrochers, 1870), and D. meridionalis Berti &amp; Rapilly, 1973 NEW STATUS. Diorhabdakoltzei ab. basicornis Laboissière, 1935 and D. e. deserticola Chen, 1961 are synonymized under D. carinulata NEWSYNONYMY. Illustrated keys utilize genitalia, including male endophallic sclerites and female vaginal palpi andinternal sternite VIII. Distribution, comparative biogeography, biology, and potential in biological control of Tamarix inNorth America are reviewed. Diorhabda elongata is circummediterranean, favoring Mediterranean and temperate forestsof Italy to western Turkey. Diorhabda carinata resides in warm temperate grasslands, deserts, and forests of southernUkraine south to Iraq and east to western China. Diorhabda sublineata occupies Mediterranean woodlands from Franceto North Africa and subtropical deserts east to Iraq. Diorhabda carinulata primarily inhabits cold temperate deserts ofMongolia and China west to Russia and south to montane grasslands and warm deserts in southern Iran. Diorhabdameridionalis primarily occupies maritime subtropical deserts of southern Pakistan and Iran to Syria. Northern climatypesof D. carinulata are effective in Tamarix biological control, especially in the Great Basin desert. Diorhabda elongata isprobably best suited to Mediterranean woodlands of northern California. Northern climatypes of D. carinata may be bestsuited for central U.S. grasslands. Diorhabda sublineata, D. meridionalis, and southern climatypes of D. carinata and D. carinulata may each be uniquely suited to areas of the southwestern U.S.

Open field host selection and behavior by tamarisk beetles ( Diorhabda spp.) (Coleoptera: Chrysomelidae) in biological control of exotic saltcedars ( Tamarix spp.) and risks to non-target athel ( T. aphylla) and native Frankenia spp.

Biological control of invasive saltcedars ( Tamarix spp.) in the western U.S. by exotic tamarisk leaf beetles, Diorhabda spp., first released in 2001 after 15 years of development, has been successful. In Texas, beetles from Crete, Greece were first released in 2004 and are providing control. However, adults alight, feed and oviposit on athel ( Tamarix aphylla), an evergreen tree used for shade and as a windbreak in the southwestern U.S. and México, and occasionally feed on native Frankenia spp. plants. The ability of tamarisk beetles to establish on these potential field hosts was investigated in the field. In no-choice tests in bagged branches, beetle species from Crete and Sfax, Tunisia produced 30–45% as many egg masses and 40–60% as many larvae on athel as on saltcedar. In uncaged choice tests in south Texas, adult, egg mass and larval densities were 10-fold higher on saltcedar than on adjacent athel trees after 2 weeks, and damage by the beetles was 2- to 10-fold greater on saltcedar. At a site near Big Spring, in west-central Texas, adults, egg masses and 1st and 2nd instar larvae were 2- to 8-fold more abundant on saltcedar than on athel planted within a mature saltcedar stand being defoliated by Crete beetles, and beetles were 200-fold or less abundant or not found at all on Frankenia. At a site near Lovelock, Nevada, damage by beetles of a species collected from Fukang, China was 12–78% higher on saltcedar than on athel planted among mature saltcedar trees undergoing defoliation. The results demonstrate that 50–90% reduced oviposition on athel and beetle dispersal patterns within resident saltcedar limit the ability of Diorhabda spp. to establish populations and have impact on athel in the field.