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Research Project: Biological Control of Invasive Weeds from Eurasia and Africa

Location: European Biological Control Laboratory

2016 Annual Report

1a. Objectives (from AD-416):
Objective 1: Explore for natural enemies, including arthropods and microorganisms, of invasive weeds identified as high priority targets by the ARS Office of National Programs, performing collections, importations and exportations in compliance with local and international regulations. High priority pests include hoary cress, swallow-worts, thistle species, giant reed, tree of heaven, French broom, and medusahead grass. Objective 2: Perform taxonomic, population genetic, and phylogeographic studies as necessary to support the successful development of biological control agents for invasive weeds. Objective 3: Identify the biological and physical parameters that affect the efficacy and safety of potential agents, including climatic conditions, host specificity, effective rearing conditions, and how interactions that occur between a target weed (e.g. hoary cress) and multiple natural enemies (e.g., a root gall weevil and a root pathogen) enhance or inhibit biocontrol.

1b. Approach (from AD-416):
The goal of the proposed research is to improve management of several important, invasive alien weeds of the contiguous United States. The Bureau of Land Management estimates that over 4,600 acres of western rangelands are lost to the spread of invasive weeds each day. Successful invaders usually lack natural enemies, which control them in their native ranges. Classical biological control is a highly cost-effective, sustainable, environmentally-sound method of controlling exotic weeds over large areas. This method requires research aimed at understanding the basic biology and ecology of target weeds and their interactions with the environment and natural enemies. Genetic characterization of target weeds in their native and adventive ranges can identify regions of origin of invasive populations and help to understand the invasion process. Foreign exploration in the region of origin provides candidate biological control agents such as insects and mites for evaluation. Host specificity and potential effectiveness of candidates will be evaluated in field and laboratory studies. Experiments will also examine the evolutionary, ecological, and physiological aspects of plant-insect interactions relevant to weed biological control. Research on yellow starthistle, hoary cress, giant reed, medusahead, and French broom will continue, and additional weeds will be targeted in response to stakeholder demand and available resources. EBCL plays a key role providing research and prospective agents to federal and state cooperators necessary for the successful control of target weeds. The research proposed here is critical to achieving ecologically rational, sustainable management of some of the most important invasive weeds in the United States.

3. Progress Report:
Objective 1 Samples of yellow starthistle (CENTAUREA SOLSTITIALIS) were collected in Greece and Bulgaria to rear out natural enemies of yellow starthistle. Sampling of giant reed (ARUNDO DONAX) canes in France provided flies of CRYPTONEVRA sp. which were sent to ARS cooperators in Edinburg, TX. Samples of the giant reed infested with the root scale (RHIZASPIDIOTUS DONACIS) and a leaf-mining midge (LASIOPTERA DONACII) were collected and shipped to cooperators in Texas for biological control of giant reed. Hundreds of the weevil LEPIDAPION ARGENTATUM were collected in France in Fall 2015 to establish colonies of this prospective biological control agent of French broom (GENISTA MONSPESSULANA). One hundred adults were shipped to the ARS quarantine in Albany, CA, to establish a colony for host specificity testing. Yet-to-be-identified insect species belonging to Chrysomelidae and to Hymenoptera (seed borers) were found on medusahead (TAENIATHERUM CAPUT-MEDUSAE) in Turkey and Italy, respectively. Collections of herbarium specimens of African wire grass (VENTENATA DUBIA) were obtained from six European countries, prepared, listed, and entered into databases. Initial collections of Sahara mustard (BRASSICA TOURNEFORTII) were made in the Mediterranean region and DNA was extracted in a collaborative project with University of California, Irvine to determine the geographic origin of the invasive weed. ACERIA SALSOLAE, a prospective biological control agent of Russian thistle, was collected in Greece to use for host specificity tests. An ARS scientist visiting EBCL surveyed countries in central and eastern Europe to collect eriophyid mites on medusahead (TAENIATHERUM CAPUT-MEDUSAE) and cheatgrass (BROMUS TECTORUM) for identification and colonization. Objective 2 Sub-objective 2a. Collections of the invasive grass, VENTENATA DUBIA, were conducted in Europe, including at least 20 populations from 6 different countries. Genetic analysis using allozymes and AFLP’s of VENTENATA DUBIA have shown a match for a genotype in western Oregon with a population collected from Slovakia, and the most common genotype found in Idaho and eastern Oregon matched a population from Hungary. Sub-objective 2b. Sampling of the weevil populations and specimens of their corresponding host, hoary cress (LEPIDIUM DRABA), was conducted at six sites on a latitudinal transect in the Rhone Valley, France, where both specialist and generalist populations are known to co-occur. Plant leaves were dried and preserved with silica gel desiccant for DNA analysis. Weevil larvae were dissected from root galls and preserved in absolute ethanol for DNA analysis. Molecular genetic analysis is ongoing to determine if there is a gene flow between host specialist and host generalist populations of the weevil. Sub-objective 2C. Dried leaves and seeds of yellow starthistle (YST) populations were sampled throughout the native range (France, Spain, Italy, Sicily, Greece, Bulgaria, and Turkey), and in the invasive range in USA (California). Herbarium specimens have been prepared. The genetic diversity of these populations was assessed using microsatellites to trace back the origin of the Californian invasive populations and to study differences in the genetic population structure between the two regions. Samples of YST and the biological control agent UROPHORA SIRUNASEVA were collected in Greece in support of research being conducted in California to evaluate the effect of host plant genotype on efficacy of this biological control agent. Objective 3 Sub-objective 3a. Seeds of different populations of hoary cress have been collected throughout the range where the weevil specialist co-occurs to set up a new field experiment aiming at evaluating the effect of the interaction of a soilborne fungus (RHIZOCTONIA SP.) and the root-gall weevil (CEUTORHYNCHUS ASSIMILIS) on the target weed, hoary cress (LEPIDIUM DRABA). Results of the previous field experiment showed that both RHIZOCTONIA alone and RHIZOCTONIA plus weevils each tended to increase plant mortality, but not significantly, mostly due to an unforeseen interaction effect. Soil samples from all the replicates of the four different treatments of the field experiment have been collected to evaluate the impact of the biocontrol agents on the diversity of soil microbes. Culturable microbes were isolated and screened for inhibitory effects against the biocontrol agent RHIZOCTONIA SOLANI. Seven fungal and three bacterial isolates were able to strongly inhibit the growth of R. SOLANI. In addition, microbial DNA was extracted from soil samples and analyzed to measure bacterial biodiversity. Bioinformatics analysis are in progress. Sub-objective 3b. A field cage experiment to test the specificity of the weevil LEPIDAPION ARGENTATUM, a prospective biological control agent of French broom (GENISTA MONSPESSULANA) was conducted to determine if nontarget lupine species are at risk of attack. No choice tests in controlled conditions were done with same lupine species. A lab experiment was conducted to understand the life cycle of the weevil, which has two modes of attack: stem-galling and seed-boring, and to determine the number of developmental stages. Field garden experiments to test the host specificity of a prospective agent of yellow starthistle, the seed-feeding weevil, LARINUS FILIFORMIS, being conducted with cooperators in Turkey were aborted due to mortality of many non-target test plants during the winter. A field garden experiment to test the host specificity of a prospective agent of Russian thistle, the eriophyid mite, ACERIA SALSOLAE, is being conducted with cooperators in Italy. 30 eggs of the leaf-feeding moth, ABROSTOLA ASCLEPIADIS, were collected in France to perform a test on Swallow wort, VINCETOXICUM SP., and for obtaining pupae in open conditions on caged plants to send to our U.S. cooperator.

4. Accomplishments
1. Grassmapper website. Invasive alien grasses can reduce forage and biodiversity of rangelands, but they are not easy to identify and mapping information is needed to help guide management decisions. Scientists at the USDA-ARS European Biological Control Laboratory in Montpellier France, Boise State University in Idaho, and the Biotechnology and Biological Control Agency in Rome, Italy have created a new website, The site provides basic biological information of three invasive grass species (ventenata, medusahead, and cheatgrass). An interactive map of the occurrence of ventenata grass is available, and will soon be accompanied by the other two species. The site was developed to aid scientists, land managers, and especially the general public to identify, and report the presence of these invasive grass species.

Review Publications
De Biase, A., Colonelli, E., Belvedere, S., La Marca, A., Cristofaro, M., Smith, L. 2016. Genetic and morphological studies of Trichosirocalus species introduced to North America, Australia and New Zealand for the biological control of thistles. Bulletin of Entomological Research. 106(1): 99-113. doi:10.1017/S000748531500084X.
Hongsheng, P., Yanhui, L., Chunli, X., Huihui, G., Xiaoming, C., Xiaoling, S., Yongjun, Z., Williams, L., Wyckhuys, K.A., Kongming, W. 2015. Volatile fragrances associated with flowers mediate the host plant alternation of a polyphagous mirid bug. Scientific Reports. 14805; doi: 10.1038/srep14805.
Von Virag, A., Bon, M., Closca, C., Diaconu, A., Haye, T., Weiss, R., Muller-Scharer, H., Hinz, H. 2016. Phenology and temperature-dependent development of Ceutorhynchus assimilis, a potential biological control agent for Lepidium draba. Journal of Applied Entomology. DOI: 10.1111/jen.12322.
Lesieur, V., Jeanneau, M., Martin, J., Bon, M. 2016. Development and characterization of 11 microsatellite markers in the root-gall-forming weevil, Ceutorhynchus assimilis (Coleoptera: Curculionidae). Applied Entomology and Zoology. DOI: 10.1007/s13355-016-0414-7.
Uludag, A., Gbehounou, G., Kashefi, J., Bouhache, M., Bon, M., Bell, C., Lagopodi, A.L. 2016. Management of Solanum elaeagnifolium in the Mediterranean Basin. European Plant Protection Organization Bulletin. 46:139-147.