My long-term goal is to develop and improve integrated biologically-based strategies to manage invasive plants. Biological weed control is a discipline with a long tradition, and recent successes. However, the major problems associated with classical weed biocontrol programs are the low success rate, only 20-30%, and the unpredictability of this success. With the help of basic research I want to elucidate the validity of some of the ecological principles underlying biological control of weeds and thus, improve the efficiency and the predictability of the outcome of weed biocontrol programs. To accomplish this goal, knowledge on the life-history of the insect species, on insect-plant interaction mechanisms, and interactions of herbivory pressure and other biotic and abiotic stresses on invasive species is required. Ecological theories relevant to biological weed control, such as the Evolution of Increased Competitive Ability (EICA) hypothesis, and Bottom-up versus Top-down Impact theories need to be substantiated through empirical data. In my opinion, these research questions can only be answered through interdisciplinary collaborative research with weed, soil, and landscape ecologists.
My research program focuses on insect-plant interactions, specifically on those between host-specific (specialist) herbivore insects used as biological weed control agents and their respective exotic invasive host plants or noxious weeds. The history and factors facilitating the invasion, the current and potential magnitude of problems, and the existence and impact of biological control programs are unique to each invasive plant. Consequently, I conduct research specific to individual invasive plant species.
All my research revolves around one of the following three themes:
Please explore in more detail the biological control research projects below organized by the targeted invasive plant. If you have any questions on a particular project, please email Mark Schwarzländer.Dalmatian Toadflax | Dyer's Woad | Hoary Cress| Houndstongue| Rush Skeletonweed| Tansy Ragwort| Yellow Starthistle
My research on Dalmatian toadflax Linaria dalmatica (L.) Miller (DTF) is in research theme 2 (see above) and focuses on the establishment and impact of a biological control agent, the stem-mining weevil Mecinus janthinus Germar (Coleoptera: Curculionidae). Unlike for rush skeletonweed and yellow starthistle, the stem-mining weevil is assumed to cause severe damage to its noxious weed host plant and we were interested in the post-release population increase of the weevil and density dependant effects on DTF plant density. Dalmatian toadflax is a herbaceous rhizomatous perennial plant in the Snapdragon family (Scrophulariaceae) that has been deliberately introduced as an ornamental into the U.S. from eastern Europe in 1894. It invades range and fallow lands with uncultivated, summer-dry, coarse soils in the western U.S. Three specialist herbivore species feeding on L. dalmatica have been inadvertently introduced with plants into North America and four biological control agents have been deliberately introduced to control L. dalmatica in North America. Of these four biological control agents, the stem-mining weevil Mecinus janthinus is assumed to be the most effective species but there is little quantitative data available on the impact of the weevil on L. dalmatica and invaded plant communities. We monitored the establishment, population increase, and impact of M. janthinus on L. dalmatica at field sites in Idaho. Several sites were lost during the course of the study to construction and/or cultivation but for three release sites of the weevil consecutive data on weevil attack rates, vegetation cover, and DTF plant parameters were collected in permanent 0.125 m² plots between 2002 and 2005. M. janthinus populations increased at all three sites with a maximum increase of 5,000% from 400 to >20,000 weevils within four years. With increasing weevil attack rates, DTF flowering stem density and cover decreased to below detectable levels at all three field sites. The resulting open space was however mostly occupied by other exotic forbs, notably spotted knapweed (Centaurea maculosa Lam., Asteraceae) rather than desirable native vegetation. We also studied relationships between weevil attack rates and DTF patchiness and found that there is a strong spatial dependency in the 5 – 70 m range between M. janthinus attack rates and DTF plant density, indicating that the weevil is following host plant patches well. We are currently developing visual (plant damage pattern) impact monitoring guidelines for agency land managers to facilitate the region wide impact assessment of the stem-mining weevil.
For Dalmatian toadflax, we were able to show that the release of even small numbers of a stem-mining weevil causes extreme abundances of this insect within four years with substantial damage to weed populations. We studied whether a biocontrol agent released in Canada to control the rangeland weed houndstongue would also attack closely related co-occuring plants in the family Boraginaceae. We found that indeed the insect utilizes co-occurring confamilial non-target species although at a very small rate and concluded that the release of the insect in the U.S. may pose environmental risks to non-target plant species.
Dyer's woad, (Istatis tinctoria) (Brassicaeae) (DW), is an invasive biennial, winter annual, or short-lived perennial; up to 3½ feet tall that invades rangeland, forest, pastures, cultivated fields, roadsides and disturbed sites. DW was introduced from Europe as a source of blue dye in colonial times. DW reproduces by seed and is thought to disperse medium to long distances given the distances between patches in southeastern Idaho.
In 2004, an initiative was started by the University of Idaho and Jim Hull (Weed Superintendent, Idaho) to investigate the potential for biological control of dyer's woad. After preliminary literature and field surveys, three insect species were prioritized as potential biological control agents, one of which, the root-crown feeding weevil Aulacobaris fallax, was not sufficiently specific. In 2006 and 2007, more thorough literature and field surveys revealed several additional biological control candidates and investigations were started on three of these.
In 2008, we continued no-choice tests for the root-crown feeding weevil Ceutorhynchus rusticus. Of 60 test plant species exposed so far, adults emerged from only five, and a multiple-choice field-cage test showed a clear preference for DW. An impact experiment conducted in 2008, by M.S. student Loic Edelmann, revealed that C. rusticus can reduce biomass of DW by 46% and seed output by 72%. No-choice larval transfer tests for the stem-mining flea beetle Psylliodes isatidis advanced well in 2008, but confirmed that P. isatidis has a relatively broad larval host range. However, like Psylliodes wrasei on hoary cress, female egg-laying behaviour under multiple-choice conditions appears to be much more specific. The seed-feeding weevil Ceutorhynchus peyerimhoffi is one of three additional agents we started to work on in 2008. Our collaborators, Dr Massimo Cristofaro (Biotechnology and Biological Control Agency; BBCA, Rome, Italy) and Dr Enzo Colonnelli (University of Rome) collected the weevil in Italy, and sent specimens to CABI Europe - Switzerland. Considering the low number of weevils available (25 females, 22 males), we made very good progress. We collected basic data on its biology and phenology, developed methods for host-specificity tests, and were able to establish a small rearing colony at CABI's Swiss centre. Host-specificity tests were also started for the other two potential agents, i.e. the root-mining weevil Aulacobaris licens and the shoot and root-crown mining flea beetle Psylliodes tricolor. Results indicate a relatively broad host range for both species under no-choice conditions. However, in preliminary choice tests P. tricolor showed a clear preference for DW and did not attack any of the test plant species exposed.
We are planning to conduct an open-field test for C. rusticus and P. isatidis in southern Germany (i.e. in an area where both species occur naturally) with species that supported development under no-choice or cage conditions. Results should give us a good indication of whether the two species can be considered for field release in North America. Host-specificity tests will be started for C. peyerimhoffi and continued for P. tricolor and potentially A. licens.
In a 2001 questionnaire for biological control priorities in Idaho conducted by Tim Prather (PSES Department, university of Idaho) and myself, Lepidium draba L. (=Cardaria draba (L.) Desv.) (Brassicaceae), hoary cress (HC) was listed most times as the noxious weed for which a biocontrol program should be developed. Following this need I facilitated the development of a consortium that coordinates ecological pre-release research and the development of biological control agents for HC (research theme 1) overseas in collaboration with Hariet Hinz (CABI Bioscience Center, Delémont, Switzerland) with financial support from state and federal agencies. For the biological control program, we conducted studies on 6 potential biological control agents, two of which are close to petitioning for release in North America. It has been realized that the selection of efficient biological control agents largely depends on a thorough knowledge of the ecology of the invasive plant species in its native and introduced range. Thus, we used the HC biocontrol program as opportunity to study mechanism that may facilitate the invasiveness of HC using biogeographic comparisons (research theme 3). Hoary cress is a perennial, rhizomatous plant that is native to southwestern and central Asia, southern Europe and the Mediterranean regions. It was introduced to North America in the mid 1800s and is currently listed as a noxious weed in three Canadian provinces and in 16 of the United States. Hoary cress occurs in a wide range of disturbed habitats including cultivated land, rangeland, pastures, along roadsides and waste areas, but thrives particularly well in riparian or irrigated areas. Infestations of HC can displace desirable rangeland forage species, are toxic to livestock, and can reduce yields, particularly in grain and alfalfa crops and orchards. The plant reproduces sexually and vegetatively through rhizomes. Molecular analyses in collaboration with John Gaskin (USDA ARS Northern Plains Agricultural Research Laboratory, Sidney, MT) using chloroplast DNA identified 41 haplotypes of L. draba sampled in Eurasia and the United States. There was little evidence for regional geographic structuring of haplotypes in either Eurasia or the U.S. or reduction in haplotype diversity in the invaded U.S. range, suggesting multiple, or few but diverse, introductions to the U.S. Ten haplotypes were found within both, the U.S. and Eurasia, representing 80% of the U.S. HC plants. Two M.S. graduate students conducted identical field studies in the weed’s introduced U.S. (Jessica McKenney) and native range (Michael Cripps). Field surveys for the arthropods associated with HC were conducted on both continents that resulted in 80 new host records for HC in Europe, and 37 new host records in the U.S. Although total species richness was nearly four times greater in Europe, there were approximately equal proportions of oligophagous and polyphagous species in each range. Monophagous species were only encountered in the European surveys. The literature surveys revealed that the arthropod fauna associated with L. draba is fairly well known in Europe (175 species), but not in the U.S. (8 species), where the literature was virtually derelict of host records. In both the literature and field surveys, the order Coleoptera contained the most species (>50%) in Europe, whereas the order Hemiptera contained the most species (>40%) in the U.S. We also studied the arthropod community composition and structure on HC in its native, expanded and introduced ranges in order to elucidate the lack of a biotic constraint that may facilitate invasion. We used identical sampling protocols collect data from a total of 35 populations of HC in its native (Eastern European), it’s expanded (Western European) and introduced (U.S.) ranges. Species richness was greatest in the native range, while species diversity and evenness were similar in the native and expanded range, but significantly greater than in the introduced range of HC. Specialist herbivore abundance was greater in the native and expanded compared to the introduced range. Oligophagous Brassicaceae feeders were equally abundant in all three ranges, and polyphagous herbivore abundance was significantly greater in the introduced range. Overall herbivore abundance was greater in the introduced range but host utilization was more complete in the two European ranges due to monophagous herbivores that do not exist in the introduced range. However, one indigenous stem mining weevil, Ceutorhynchus americanus Buchanan (Coleoptera: Curculionidae), occurred on HC in the introduced range. We believe that this is the one of the first studies documenting greater herbivore abundance on an invasive weed in its introduced compared to its native range. Greater abundance does not necessarily translate to greater impact and we argue that despite the greater total herbivore abundance in the introduced range, differences in the herbivore community structure, i.e. specialist versus generalist herbivory, may contribute to the invasion success of HC in the U.S. We also used the biogeographic comparison of native European and introduced U.S. populations of HC to test 1) whether performance differences of the plant between the native and introduced range exist, 2) whether these differences are consistent between years, and 3) whether potential differences provide support for specific invasion mechanisms. We collected data at 62 HC populations in Europe and the U.S. In addition to plant and plant population traits and endophagous herbivory, we also assessed vegetation cover and soil nitrogen pools for each population. Surprisingly, we found no difference in population size between ranges. However, density, cover, biomass and individual plant size of HC were consistently greater in the introduced range in the U.S., while cover of other vegetation was reduced. HC seed output was greater in the U.S. range in only one of the two years, as was the availability of labile soil nitrogen and the proportion of bare ground and litter. The frequency and intensity of endophagous shoot herbivory was reduced in the introduced range. Five insect species were reared from attacked shoots in Europe, but only one native species, the weevil C. americanus, was reared from attacked shoots in the U.S. There are substantial ecological differences for L. draba populations between ranges that are consistent with predictions of the enemy release and biotic resistance hypotheses: Hoary cress populations experience less specialist herbivory and inter-specific competition in the introduced range and profit from greater nutrient availability and empty niches, both of which may result in denser and more vigorous plants in areas where HC is invasive. The results do not contradict predictions of the evolution of increased competitive ability (EICA) and novel weapons hypotheses, thus limiting conclusions that can be drawn from this type of study. We also conclude that inconsistent results between years for some of the measured traits emphasize the importance to conduct geographic comparisons for more than one field season. In addition to these descriptive biogeographic comparisons, we conducted two common garden studies to specifically test the test for the evolution of increased competitive ability of HC. The EICA hypothesis states that plants introduced into a new range experience reduced herbivory, which in turn results in a shift in resource allocation from herbivore defense to growth. If genotypes of an invasive plant species from its native and introduced ranges are grown under common conditions, introduced genotypes are expected to grow more vigorously than conspecific native genotypes. We tested these predictions for HC by comparing the growth of genotypes from Europe and the U.S. under common conditions. To test potential differences in competitive ability, we grew L. draba from both continents with either Festuca idahoensis, a weak competitor native to North America, or Festuca ovina, a strong competitor native to Europe. Contrary to EICA predictions, there were no differences in the performance of native and introduced HC, independent of whether plants were grown with F. idahoensis, F. ovina, or alone. The strong competitor, F. ovina impaired the growth of L. draba more than the weak competitor F. idahoensis and conversely, F. idahoensis was generally more impaired by HC than was F. ovina. While the native F. idahoensis was equally strong affected by L. draba regardless of range, F.ovina was not: U.S. L. draba had a stronger negative effect on F. ovina growth than European HC. Our data suggest that the EICA hypothesis is not suitable to explain the invasion success of L. draba in the U.S. Instead, the greater competitive effect of HC on the North American F. idahoensis and the asymmetric competitive effect of HC from different origins on F. ovina may indicate superior competitive ability for resources, or the presence of allelopathic traits in HC, to which plant species in non-native ranges are maladapted. We currently test the presence of allelopathy in HC and the related novel weapons hypothesis.
Enemy release (ERH) and the evolution of increased competitive ability (EICA) are two plant invasion hypotheses assuming that the absence of coevolved host-specific herbivore insects facilitate the invasiveness of plant species in the introduced range. Because of the direct implications for biological weed control, we tested both hypotheses parallel for the exotic mustard hoary cress. While we did not find support for the evolution of competitive ability, the absence of specialist herbivores may benefit hoary cress. A biological control program would consequently be justified for this noxious weed.
Houndstongue, Cynoglossum officinale (Boraginaceae) (HT), is a noxious biennial or short-lived perennial weed of mountainous rangelands in northwestern North America. Native to Europe, this weed was likely introduced as a contaminant of cereal seed in the 1800’s and is nowadays invasive in many western U.S. states, Alberta, and south central British Columbia. Especially cattle producers in these areas consider HT to be one of the most serious rangeland problems. The seeds that are borne in burred nutlets attach easily and mat to livestock hair, which causes irritation in animals and reduces livestock price. In addition, HT is highly toxic to cattle and horses and deaths have been reported. My research program on houndstongue addresses all three research themes. We are conducting research that hopefully will lead to the introduction of a new biological control agent, we studied the environmental safety of a biocontrol agent released in Canada but not the U.S. and we use HT to test a recent plant invasion hypothesis. Reports on nontarget effects of deliberately introduced biological control agents at the individual plant and population level have caused debate over the safety of biological control of weeds in the U.S. One result of the ongoing dialogue how to improve biological weed control practices is the mandatory monitoring and reporting of nontarget effects as part of post-release assessments. This is particularly important in the case of the root-mining weevil Mogulones cruciger (Herbst) (Coleoptera: Curculionidae), which was released in Canada to control HT but not in the U.S. Mogulones cruciger was first released in 1997, following recommendations of the Technical Advisory Group and the Canadian Biological Control Review Committee. During the same year, the U.S. Fish and Wildlife Service raised concerns about the potential for nontarget effects by the weevil to an endangered-listed Boraginaceae species. To assess the environmental safety of the weevil and the potential for nontarget effects, we identified and monitored all co-occurring confamilial Boraginaceae species at six M. cruciger release sites in Alberta and British Columbia over a two-year period. All four co-occurring species found at field sites were attacked by the weevil to varying degrees although attack was inconsistent between years and sites. Nontargets were attacked to a lesser degree than HT but differences were not consistently significant for species, sites, or years. There was a positive relationship between the probability of nontarget attack and C. officinale attack rate by M. cruciger. Since there is no information on the host choice behavior of the weevil our data suggest that the release of M. cruciger in the U.S. may pose at least transitorily risks to native Boraginaceae. In collaboration with Sanford Eigenbrode (PSES Department, University of Idaho), we expanded this research to collect preliminary data on volatile organic compounds (VOC) in the headspace of HT and native confamillials, the behavioral response of M. cruciger to VOC using a 4-arm olfactometer, and on gas chromatography with simultaneous electroantennogram detector and flame ionisation detector (GC/FID/EAD). Our preliminary data of combined behavioral and electrophsiological bioassays indicate that female M. cruciger react indeed to the headspace VOC collected from HT and related plant species, and that at least two nontarget confamilials found at HT field sites are less attractive to M. cruciger females than HT. For a congener of M. cruciger, the seed-feeding weevil, Mogulones borraginis, we conduct host-specificity in order to determine whether the insect is safe for introduction into North America. Foreign exploration for this extraordinary host-specific potential biocontrol agent is completed with the exception of tests with native North American Cynoglossum-species. We received a USDA permit for experimental quarantine introduction of the weevil in 2005 and discovered field populations of the three critical native plant species during the same year. We conducted first host-specificity tests with these plants at the Northwestern Biological Control Quarantine at Washington state University, Pullman, WA in collaboration with Terry Miller Department of Entomology, WSU) and provided root stocks to our other collaborators on this project, Hariet Hinz (CABI Bioscience Center Switzerland, Delémont, Switzerland) and Rosemarie DeClerck-Floate, (Agriculture and Agri-Food Canada, Lethbridge, AB). Houndstongue toxicity is due to large quantities of pyrrolizidine alkaloids (PAs), the primary chemical defense system of this plant species. Because PAs are known to be inducible, we tested in collaboration with Sanford Eigenbrode a recently proposed plant invasion mechanism, which has received much attention, the evolution of increased competitive ability (EICA) hypothesis. The EICA hypothesis predicts that invasive plant populations in their introduced ranges, where they have escaped herbivore pressure, will evolve lower concentrations of defensive secondary chemicals than populations of the same species in their native range, and allocate the saved resources to competitive traits. The hypothesis as originally formulated did not consider the implications of the widespread phenomenon of induction of plant defenses in response to herbivory. A modification of EICA incorporating inducible defenses predicts that the mean levels of induced defenses do not differ between introduced and native ranges, but the levels will be will be more variable in the introduced range. This should occur if reduced herbivory in the native range limits induction, preventing exposure to natural selection, whereas in the native range stabilizing selection can act to restrict induced chemical defenses closer to optimal levels. We conducted a preliminary study to examine this by comparing constitutive and induced concentrations of total PAs from native European and introduced North American populations of HT. The mean constitutive and induced concentrations of PAs did not differ between continents, but the variability of the induced concentrations was significantly greater for plants from the introduced range. This result is consistent with the predicted pattern of a modification of EICA that considers inducible defenses. The implications of the result is that inducible defenses can obscure or prevent manifestation of EICA as it was originally formulated, that studies to detect EICA in other species should consider the effect of induction on patterns of chemical defense in native and introduced ranges, and the greater variability in inducible defenses in the introduced range of an invasive species could contribute to variable susceptibility of introduced populations to biological control agents.
Rush skeletonweed, Chondrilla juncea L. (Asteraceae) (RSW), is an apomictic, herbaceous perennial indigenous to the Mediterranean area and central Asia. It has been inadvertently introduced into Argentina, Australia, and North America. In the U.S., it is a major problem in rangeland and semiarid pastures in California, Oregon, Washington and especially in Idaho, where it infests more than 6 million acres of non-agricultural lands.
My research on rush skeletonweed addresses above research themes 1 and 2. Although the need for quantitative post-release monitoring studies testing these assumptions has been acknowledged repeatedly, the number of assessments is still remarkably small and usually restricted to systems with notable impact of an agent species. However, studying systems where biological control agents cause no observable target weed reductions may be important to identifying factors that limit the population size or impact of biological control agent species.
Three biological agents were released for the control of rush skeletonweed in North America between 1975 and 1977. Although all three species are widely established, weed densities are increasing and there is little quantitative information on factors limiting biological control efficacy. Laboratory studies indicated for a great control potential for at least two of the biological control agents: the rush skeletonweed gall mite, Aceria chondrillae Canestrini (Acari: Eriophyidae) and the rush skeletonweed rust, Puccinia chondrillina Bubak and Sydenham. We examined the impact of A. chondrillae and P. chondrillina on rush skeletonweed at two field sites in southwestern Idaho. We excluded A. chondrillae and P. chondrillina using a miticide and a fungicide, respectively, and compared plant growth parameters between unprotected and protected plants. Neither A. chondrillae, P. chondrillina, nor both species combined reduced aboveground biomass of rush skeletonweed at present biocontrol agent densities. While both biocontrol agents reduced the number of flowers and consequently the reproductive output at one field site this was not the case for the other field site. We assumed that the population limiting factors exist for each of the tow biocontrol agents. We examined the winter biology and survivor ship of A.chondrillae at two rush skeletonweed field sites in southwestern Idaho over two years and found that gall mite winter mortality was high (> 90%) in both years and for both sites. Gall mites were also more abundant on plants that produced rosettes in fall and rush skeletonweed plants growing on southern aspect were 3.4 more times likely to produce rosettes than those growing on northern aspects. The data suggest that A. chondrillae population densities are limited by its high winter mortality. We believe that the gall mites may require fall rosettes to successfully survive the winter, which are commonly absent on north-facing aspects, impairing the efficacy of A. chondrillae. For the fourth agent, the root-boring moth Bradyrrhoa gilveolella (Treitschke) (Lepidoptera: Phycitidae), permission for field release in the U.S. was granted in 2002. The moth was introduced and released in Australia in the 1980s but never established. We are currently the only lab in North America that can mass rear this biological control agent. While providing other states with egg masses of the moth for rearing programs, we have reared sufficient numbers to start studying the post-release establishment at field sites throughout Idaho.
We also study potential plant resistance of rush skeletonweed as a first step to better match virulent biotypes of biocontrol agents with invasive plant genotypes. For this we are testing anecdotal reports on the existence of distinct biotypes of RSW in the U.S. that differ in phenology, morphology and host plant resistance. We compared the flowering phenology for 40 U.S. populations under standardized conditions in a greenhouse and currently test the susceptibility to the different biocontrol agents. We have expanded this work with a colleague, Dr. John Gaskin, at the USDA ARS Northern Plains Agricultural Research Laboratory, Sidney, MT, who collected ALFP data for these 40 populations to compare it to populations in Australia, Argentina, and Eurasia. While we do not know yet where the U.S. populations originated in Europe and how closely related they are to the three known Australian genotypes, there is indication for the presence of distinct genotypes in the U.S. and also for resistance of populations to the RSW rust.
I also collaborate with Dr. George Newcombe (Department of Forest Resources) and Dr. Cort Anderson (Department of Fish and Wildlife) to test pathogensis and virulence of different U.S. accessions of the rust and we hope to differentiate rust genotypes molecularly. As part of this collaboration we found that the RSW rust, P. chondrillina is attacked by the fungal mycoparasite Eudarluca caricis, which may well limit the efficiency of the rust to control the invasive plant.
For Rush Skeletonweed, we have shown that one of the established biological control agents is limited by high winter mortality whereas another agent, a rust fungus causes a reduction of rush skeletonweed flowers despite the fact that it is attached by a hyperparasite. We consequently rear and try to establish a new root-mining biocontrol agent for rush skeletonweed.
My research on tansy ragwort, Senecio jacobaea L. (Asteraceae) (TRW) addresses the first research theme. Tansy ragwort is an exotic invasive, which is listed as noxious weed in 8 western states. Native to Eurasia and it was introduced - and has become invasive in Australasia, South Africa, and South- and North America. Tansy ragwort is a facultative monocarpic short-lived perennial, especially under poor soil conditions. If soil conditions are favorable TRW behaves typically as a biennial. In the U.S., the successful control of large infestations of TRW west of the Cascade Mountain range is primarily attributed to the introduction of the flea beetle Longitarsus jacobaeae Waterhouse (Coleoptera: Chrysomelidae). In contrast, biological control by this or one of the other two deliberately introduced insect species does not seem to have any measurable impact on TRW populations east of the Cascade Mountain range where the plant grows more slowly due to the shorter growing season. In addition, the precise effects of L. jacobaeae on TRW distribution and abundance are confused by the existence of two distinct strains of the flea beetle. An Italian and a Swiss strain of L. jacobaeae, which are morphologically indistinguishable exhibit different life history characteristics and their relative efficacy as tools to control the spread of tansy ragwort in different regions under different climatic regimes, is unclear. Additionally, both strains of L. jacobaeae may have different host plant ranges. The two strains readily interbreed in laboratory studies, and hybrids show life cycle characteristics different from either parental strain. Both L. jacobaeae strains were initially released in Northern California. At this point, it is not known which biotype(s) currently provide control of tansy ragwort infestations in coastal regions, and/or whether both strains or hybrids have established in the U.S., Conversely, it is possible that both strains have interbred, resulting in populations with blended life cycle and other biological traits. We are currently mass rearing a newly introduced Swiss strain of L. jacobaeae for release on TRW in the Intermountain West. In contrast to Oregon collected Italian strain beetles, our Swiss strain beetles successfully established in the winter-cold Intermountain West climate. Parallel to this effort, we want to evaluate the genetic structure of successful flea beetle populations in coastal areas. In collaboration with Eric Coombs (Oregon Department of Agriculture, Salem, OR), Massimo Cristofaro (BBCA, Rome, Italy), Urs Schaffner (CABI Bioscience, Delémont, Switzerland), and Cort Anderson (Department of Fish and Wildlife, University of Idaho), we want to develop genetic markers to reliably distinguish the Swiss and Italian strains (and potentially existing hybrids) of L. jacobaeae occurring in the U.S. We extracted DNA from 21 exemplars of the Swiss strain and 12 of the Italian strain of L. jacobaeae We sequenced a 472 bp long, contiguous region, which was common to all samples. Within this region, we detected 12 polymorphic sites, and 13 unique haplotypes. This level of polymorphism is strikingly high, when compared to other chrysomelids. These preliminary results show that there is substantial sequence variation in the mitochondrial genome of L. jacobaeae, both within and between strains, suggesting that further investigation of other regions will yield genetic markers indicative of strain type. Since these results are unexpectedly encouraging, a more comprehensive sampling of beetles is warranted in order to ensure that our sampling is representative and to begin comparisons of genetic traits of L. jacobaeae within and between different climatic regions.
We use tansy ragwort to test the common notion that climatic matching of biocontrol agent populations may improve the establishment and impact of biological weed control. We found, that in contrast to the Mediterranean genotype of a root-mining flea beetle, a cold adopted Swiss genotype successfully overwintered in the Intermountain West and we are currently studying establishment rates and impact of this flea beetle genotype.
My research on the invasive yellow starthistle, Centaurea solstitialis L. (YST) aims to assess the impact of abundant biocontrol agents and thus addresses research theme 2 but also includes a restoration ecological component. Hell’s Canyon is the deepest river gorge in the U.S., and is home to one of the last surviving pristine bunchgrass communities of the Pacific Northwest. Yellow starthistle, invaded this unique ecosystem in the early 1990’s. It now infests more than 10,000 acres of prime wildland and represents one of the area’s greatest threats to biodiversity. The biological control program for YST in Hells Canyon was initiated by Dr. McCaffrey (PSES Department) in the early 1990s. While the USDA is presently investigating new agents, four seed-head biocontrol insect species are currently established in Hell’s Canyon. These include the fruit fly Chaetorellia succinea Hering (Diptera: Tephritidae) and the weevils Bangasternus orientalis Capiomont, Larinus curtus Hochhut, and Eustenopus villosus Boheman (all Coleoptera: Curculionidae). The effects of these insects have been monitored in California but there is concern about the lack of cause and effect studies demonstrating the impact of biological control on this invasive plant. We set up a long term large scale field study to determine the net impact of biological control on YST at four field sites in Hell’s Canyon using insecticide enclosure experiments. Herbivory was reduced from 73% to 23% attacked seed-heads in treated plots in the first year of the study. Surprisingly, there was no difference for plant stature, biomass, YST density or number of buds produced between treatments. There were also no differences for the total number and number of viable seeds produced between treatments. Continuation of this study will show whether the lack of impact despite high insect abundance and attack rates was an exceptional result for 2005 or indeed part of a pattern indicating that YST can compensate for herbivory through additional flower production. There are very few empirical studies which examine the direct impact invasives have on native species and/or biodiversity. There is even less known about the direct effects of YST on native plant populations in any portions of its spreading range. In the Hell’s Canyon ecosystem, there are numerous native plant species, some of which are endemic and/or rare, whose habitat has been encroached by YST. An understanding of the interspecific effects of YST invasions is crucial for the proper management of YST and the simultaneous protection of threatened native species. Thus, a second long study was set up to determine potentially negative competitive effects of YST on a rare, native plant species in Hell’s Canyon and whether inundative releases of biocontrol agents can alleviate these effects. Crepis bakeri Greene ssp. idahoensis Babc. & Stebb. is listed as a sensitive species by the USDI Bureau of Land Management. In one region of Hell’s Canyon, a large population of this species was found interspersed among both pristine, native communities and disturbed areas highly invaded by YST and other exotics. We set up nine plot systems (and additional non-invaded control plots), in which we test the effects of different management practices including biological control and weeding of yellow starthistle and other exotics on the performance and population biology of C. bakeri and native vegetation cover. We only have collected data for one field season and although it is too early to make conclusions, there is indication that YST and certainly all exotics combined do impair C. bakeri. Removal of exotics increases the amount of bare ground rather than the cover of native vegetation. We, plan to include a treatment adding seeds of native grasses for the following field seasons.
The exclusion of four seed-head biocontrol insects released to control yellow starthistle in the field using insecticides demonstrated that combined these insects reduce viable seed production only marginally despite the great abundance of biocontrol agents.