Progress 10/01/02 to 09/30/07
Outputs
OUTPUTS: We compared the growth and insect herbivory of the invasive mustard weed hoary cress (Lepidium draba) in the western U. S. and Europe. The data set represents one of the most comprehensive bio-geographic comparisons of an invasive herbaceous plant between its native and invasive range and greatly helps to identify why this and similar plant species may be invasive in North America. L. draba shoot density, biomass per unit area, individual stem and reproductive biomass, cover, and patch size are greater for infestations in North America compared to Europe. The proportion cover of grasses and forbs was in both study years (2002 and 2003) greater in Europe. The proportion cover bare ground and litter, an indicator for opportunity of invasion was greater in 2002 in the U.S. but no difference was found for 2003. These results do indicate that plant competition is less in the U.S. and open space to invade is greater in the U.S. when compared to Europe. The comparison of the
herbivorous insect communities associated with hoary cress in Europe and the U.S. revealed that species richness, and number and diversity of specialist herbivores, i.e., those that feed exclusively on hoary cress and few closely related plant species is greater in Europe. In contrast, the abundance of generalist herbivores was greater in the invaded range. More surprisingly, the total number of herbivore insects found on hoary cress plants was almost 2.5 times larger for the U.S., however this difference was not significant between continents. Our comparative data provided support for the Enemy Release Hypothesis (ERH) as a mechanism to explain the invasiveness of hoary cress in North America. This was confirmed by experiments testing the density dependant effects of generalist and specialist herbivory on hoary cress growth. In contrast, two greenhouse experiments testing another invasion mechanism, the Evolution of Increased Competitive Ability (EICA) hypothesis, showed that this is
an unsuitable mechanism to explain the invasiveness of L. draba. We did not find any indication for growth differences alone or in the presence of a European or North American grass for L. draba populations originating in Europe or the U.S. We conducted experiments on the induction of (glucosinulate) plant defense using numerous genotypes and provenances from the U.S. and Europe. We found that glucosinulate profiles differed only marginally between ranges independent of whether they were induced or not. We continued experiments investigating potential allelopathic effects of hoary cress glucosinulates on plant neighbors. Overall, we conclude that a lack of biotic resistance and the release from specialist natural enemies may explain the invasiveness of hoary cress in North America. Therefore, our involvement in the foreign exploration for biological control agents for L. draba seems highly justified as a result of the research conducted under this project.
PARTICIPANTS: Project work was conducted by Mark Schwarzlaender (PI) and Bradley Harmon (Research Support Scientist, Universty of Idaho). Much of the research and training providd under the project was conducted in collaboration with CABI Europe - Switzerland. The University of Idaho has an MoU with CABI that facilitates collaborative research and graduate student training. Three graduate students were trained at the University of Idaho under this project: Michael Cripps (Masters of Science), Jessica McKenney (Masters of Science), and Kenneth Puliafico (Ph.D.).
Impacts
In general, our research contributes to a better understanding of the factors that facilitate the invasiveness of herbaceous plant species in the U.S. Hoary cress is one of the most invasive plant species in rangelands, grasslands and natural areas in the western U.S. The results of this research project validated the potential and importance of biological control as a promising long term management strategy for hoary cress. Since biological control foreign exploration commenced at the same time as did this project, candidate agents are close to petitioning for release in the U.S. and the research sites used for this project will serve as release sites for biological control agents. That way, the data collected under this project will be used as biological control pre-release data. Biological control of hoary cress offers an efficient biologically based management strategy for this cruciferous invasive weed that will greatly reduce the use of herbicides and exposure of
land managers to herbicides when controlling this weed.
Publications
- McKenney, J.L, Cripps, M.G., Price, W.J., Hinz, H.L., and Schwarzlaender, M. 2007 No difference in competitive ability between invasive North American and native European Lepidium draba populations. Plant Ecology. 193:293-303
- Puliafico, K. P., Schwarzlaender, M., Hinz, H. L., and Harmon, B. L. 2008. The use of surrogate herbivores for the pre-release efficacy screening of biological control agents of Lepidium draba. In Proceedings of the XII International Symposium on Biological Control of Weeds (eds. Julien, M., Hinz. H.L., Sforza, R., Claude-Bon, M. & Hector, B.), CSIRO & USDA ARS, La Grande Motte, France. Accepted.
- Lau, J.A.; Puliafico, K.P.; Kopshever, J.A.; Steltzer, H.; Jarvis, E.P.; Schwarzlaender, M.; Strauss, S.Y.; and Hufbauer, R.A. 2008. Effects of activated carbon on plant growth complicate the inference of allelopathic effects. New Phytologist. Accepted.
- Puliafico, K.P.; Schwarzlaender, M.; Harmon, B.L.; and Hinz, H.L. 2008. Effect of generalist insect herbivores on Lepidium draba (Brassicaceae) in its introduced range: implications for the enemy release hypothesis. Journal of Applied Entomology. Accepted.
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Progress 01/01/06 to 12/31/06
Outputs
The comparison of hoary cress (Lepidium draba) growth and herbivory between the western U. S. and Europe was completed during and the results are currently published. The data set represents one of the most comprehensive bio-geographic comparisons of an invasive herbaceous plant between its native and invasive range. L. draba shoot density, biomass per unit area, individual stem and reproductive biomass, cover, and patch size are greater for infestations in North America compared to Europe. The proportion cover of grasses and forbs was in both years greater in the native range, Europe. The proportion cover bare ground and litter, an indicator for opportunity of invasion was greater in 2002 in the U.S. but no significant difference was found for 2003. These results do indicate that plant competition is less in the U.S. and open space to invade is greater in the U.S. when compared to Europe. The comparison of the insect communities associated with hoary cress in Europe
and the U.S. revealed that species richness, and number and diversity of specialist herbivores, i.e., those that feed exclusively on hoary cress and few closely related plant species is greater in the native range. In contrast, the abundance of generalist herbivores was greater in the invasive range. More surprisingly, the total number of herbivore insect individuals found at hoary cress infestations was almost 2.5 times larger for infestations in the U.S., however this difference was not significant between continents. Therefore, the Enemy Release Hypothesis (ERH) is still a suitable mechanism to explain the invasiveness of hoary cress in North America. This was confirmed by experiments testing the density dependant effects of generalist and specialist herbivory on hoary cress growth. In contrast, two greenhouse experiments testing for Evolution of Increased Competitive Ability (EICA) showed that this is an unsuitable mechanism to explain the invasiveness of hoary cress. We did not
find any indication for growth differences alone or in the presence of a European or North American grass for populations originating in Europe or the U.S. We conducted experiments on the induction of (glucosinulate) plant defense using numerous genotypes and provenances from the U.S. and Europe. We found that glucosinulate profiles differ significantly between ranges independent of whether they were induced or not. We continued experiments investigating potential allelopathic effects of hoary cress glucosinulates on plant neighbors. We currently conclude that a lack of biotic resistance and the release from specialist natural enemies may explain the invasiveness of hoary cress in North America. We also continued foreign exploration research for biological control agents and will hopefully be able to petition the first insect following the 2007 field season.
Impacts
Our research contributes to a better understanding of the basic factors that facilitate invasiveness of herbaceous plant species in the U.S. We develop biologically based long-term management strategies for cruciferous noxious weeds of the western United States. Specifically, we try to understand for our model invasive, hoary cress, the factors that allow it to be such a successful invader in the western U.S. Parallel to that research effort, we develop efficient biologically based management strategies for this cruciferous invasive weed.
Publications
- Milan, J.D., Harmon, B.L., Prather, T.S. and Schwarzlaender, M. 2006. Winter mortality of Aceria chondrillae, a biological control agent released to control rush skeletonweed (Chondrilla juncea) in the western United States. J. Appl. Ent. 130(9-10):473-479.
- Cripps, M.G., McKenney, J.L., Hinz, H.L., Price, W.J. and Schwarzlaender, M. 2006. Biogeographic comparison of the arthropod herbivore communities associated with Lepidium draba in its native, expanded and introduced ranges. J. Biogeography 33:2107-2119.
- Cripps, M.G., Hinz, H.L., McKenney, J.L., Harmon, B.L., Merickel, F.W. and Schwarzlaender, M. 2006. Comparative survey of the phytophagous arthropod faunas associated with Lepidium draba in Europe and the western United States, and the potential for biological weed control. Bio. Sci. Tech. 16(10):1007-1030.
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Progress 01/01/05 to 12/31/05
Outputs
The comparison of hoary cress (Lepidium draba) growth and herbivory between the western U. S. and Europe was completed during 2005. The data set represents one of the most comprehensive bio-geographic comparisons of an invasive herbaceous plant between its native and invasive range.L. draba shoot density, biomass per unit area, individual stem and reproductive biomass, cover, and patch size are greater for infestations in North America compared to Europe. The proportion cover of grasses and forbs was in both years greater in the native range, Europe. The proportion cover bare ground and litter, an indicator for opportunity of invasion was greater in 2002 in the U.S. but no significant difference was found for 2003. These results do indicate that plant competition is less in the U.S. and open space to invade is greater in the U.S. when compared to Europe. The comparison of the insect communities associated with hoary cress in Europe and the U.S. revealed that species
richness, and number and diversity of specialist herbivores, i.e., those that feed exclusively on hoary cress and few closely related plant species is greater in the native range. In contrast, the abundance of generalist herbivores was greater in the invasive range. More surprisingly, the total number of herbivore insect individuals found at hoary cress infestations was almost 2.5 times larger for infestations in the U.S., however this difference was not significant between continents. Analysis of the insect community data indicates that specialist herbivore pressure on hoary cress is greater in Europe but also that generalist herbivore pressure on hoary cress is greater in the U.S. If the release from natural enemies contributes to the invasion success of hoary cress in the U.S., then we have to assume that herbivory inflicted by specialist herbivores impairs hoary cress growth more than does herbivory inflicted by generalists. We conducted respective experiments to test this
hypothesis. We also conducted a greenhouse study in 2004, comparing the growth of ten populations from Europe and ten populations form the U.S. In addition, we tested whether the growth of these populations differs in the presence of a native North American and a European grass. We did not find any indication for growth differences alone or in the presence of a European or North American grass for populations originating in Europe or the U.S. We are currently growing a genotype garden to repeat some earlier experiments based on genotype rather than population origin. We also started experiments that specifically test the role of glucosinulates as allelopathic substances that might facilitate hoary cress invasions in North America. Based on our findings thus far, we can exclude the evolution of increased competitive ability (EICA hypothesis) as a potential invasion mechanism for hoary cress. Enemy release (ERH) may play a role but only if specialist herbivore feeding influences hoary
cress more than generalist feeding. We are currently testing whether the lack of biotic resistance may explain the invasiveness of hoary cress in North America.
Impacts
Our research contributes to a better understanding of the basic factors that facilitate invasiveness of herbaceous plant species in the U.S. We develop biologically based long-term management strategies for cruciferous noxious weeds of the western United States. Specifically, we try to understand for our model invasive, hoary cress, the factors that allow it to be such a successful invader in the western U.S. Once these factors are identified, we hope to develop more efficient biologically based management strategies for this and related invasive species. We also hope that our research on hoary cress contributes to a better understanding of the ecology of herbaceous invasive plants.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
The field work for the comparison of heart-podded hoary cress (Lepidium draba) growth patterns and herbivory in the western U. S. and Europe has been completed in 2004. Data analysis is almost completed and the data set represents one of the most comprehensive bio-geographic comparisons of an invasive plant species in its native and invasive range. In short, L. draba shoot density, biomass per unit area, individual ramet biomass, reproductive biomass, cover, and patch size are greater at infestations in North America compared to Europe. The proportion cover of grasses and forbs, an indicator for interspecific competition was in both years greater in the native range, Europe. The proportion cover bare ground and litter, an indicator for opportunity of invasion was greater in 2002 in the U.S. but no significant difference was found for 2003. These results do indicate that plant competition is less in the U.S. and open space to invade is greater in the U.S. when compared
to Europe. The comparison of the insect communities associated with hoary cress in Europe and the U.S. revealed that species richness, and number and diversity of specialist herbivores, i.e., those that feed exclusively on hoary cress and few closely related plant species is greater in the native range. In contrast, the abundance of generalist herbivores was greater in the invasive range. More surprisingly, the total number of herbivore insect individuals found at hoary cress infestations was almost 2.5 times larger for infestations in the U.S., however this difference was not significant between continents. The preliminary analysis of the insect community data indicates that specialist herbivore pressure on hoary cress is greater in Europe but also that generalist herbivore pressure on hoary cress is greater in the U.S. If the release from natural enemies contributes to the invasion success of hoary cress in the U.S., then we have to assume that herbivory inflicted by specialist
herbivores impairs hoary cress growth more than does herbivory inflicted by generalists. We also conducted a greenhouse study in 2004, comparing the growth of ten populations from Europe and ten populations form the U.S. In addition, we tested whether the growth of these populations differs in the presence of a native North American and a European grass. We did not find any indication for growth differences alone or in the presence of a European or North American grass for populations originating in Europe or the U.S. We are currently growing a haplotype garden to repeat this experiment based on haplotype rather than population origin. This research contributes to a better understanding of the factors that facilitate invasiveness of herbaceous plant species in the United States. We are using hoary cress as a model system to test whether current invasiveness theories such as the biotic resistance hypothesis (BRH), the enemy release hypothesis, or the evolution of increased competitive
ability (EICA hypothesis), apply to the invasion success of this mustard weed.
Impacts
Our research contributes to a better understanding of the basic factors that facilitate invasiveness of herbaceous plant species in the United States. We develop biologically based long-term management strategies for cruciferous noxious weeds of the western United States. Specifically, this research accelerates the development of integrated management strategies through pre-release screening of the most efficient insect biological control - plant competition combination to successfully manage hoary cress. The research will also determine inefficient insect herbivores that may be disregarded as potential biological control agents for hoary cress, thus economizing resources and time.
Publications
- Hinz, H.L. and Schwarzlaender, M. 2004. Comparing invasive plants in their native and exotic range: What can we learn for biological control? Weed Technology. 18:1533-1541.
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Progress 01/01/03 to 12/31/03
Outputs
We continued to analyze hoary cress (L. draba) infestations in Idaho and adjacent states and compared plant growth and herbivory pressure in the western United States with data concurrently collected at hoary cress field sites in central and eastern Europe. Heart podded hoary cress is prevalent in riparian areas in southern Idaho and southeastern Oregon. In the Idaho panhandle, the plant species causes fewer problems, however, infestations in hay crop increase at a fast rate. In North America hoary cress biomass per unit area is almost four times as large as in Europe. The increased biomass in North America can be explained through a higher shoot density per unit area. Individual shoot biomass between continents does not differ significantly. The mean number of stems per 12.5 cm by 25 cm rectangle was 12.48 for North American and 3.40 for European field sites (P < 0.001). There are large differences in the phytophagous insect fauna associated with the crucifer weed
between North America and Europe. Thus far, the most common insect species found feeding on hoary cress at North American field sites were polyphagous plant bugs in the genus Lygus, particularly L. hesperus Knight (Hemiptera, Miridae). On average, more than 42 Lygus adults and nymphs were found per 10 sweeps at North American heart-podded hoary cress field sites. At European field sites, Lygus individuals were rarely found on the plants. For thrips and mites the results were similar. In contrast to oligophagous insect pest species, the number of specialist insect herbivores, e.g., monophagous and/or strictly oligophagous weevil species such as Ceutorhynchus erysimi (F.), and C. americanus Buchanan (Coleoptera, Curculionidae), was smaller in North America when compared to Europe. In North America 0.88 specialist species were found at field sites compared to 5.56 species per site in Europe (P < 0.001). In sum, the herbivory pressure (number of insects and mites per unit area) was
similar for both continents but insect and mite guilds differ. The proportion of specialist herbivores of hoary cress is larger in Europe and the proportion of polyphagous and oligophagous insect pests is larger in North America. After the quantification of plant growth and insect guild composition, we plan to conduct experiments that will allow us to quantify the relative impact of North American insect guilds and European insect guilds on hoary cress growth and population biology. With a different set of experiments we will try to understand whether there are differences between North American hoary cress genotypes in insect-feeding tolerance.
Impacts
Our research contributes to a better understanding of the basic factors that facilitate invasiveness of herbaceous plant species in the United States. We develop biologically based long-term management strategies for cruciferous noxious weeds of the western United States. Specifically, this research accelerates the development of integrated management strategies through pre-release screening of the most efficient insect biological control - plant competition combination to successfully manage hoary cress. The research will also determine inefficient insect herbivores that may be disregarded as potential biological control agents for hoary cress, thus economizing resources and time.
Publications
- No publications reported this period
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