Location: European Biological Control Laboratory2017 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:
Progress was made on all three objectives and their subobjectives, all of which fall under National Program 304, Crop Protection and Quarantine, Component 2: develop innovative control methods and integrated pest management (IPM) strategies for weeds, regarding Problem Statement 2A3: Systems approach to environmentally sound weed management in cropping systems and Problem Statement 2B3: Systems approach to environmentally sound weed management in natural ecosystems. Under Objective 1 we made significant progress in exploration for prospective biological control agents of several target weeds. The weevil (LEPIDAPION ARGENTATUM), a prospective biological control agent of French broom (GENISTA MONSPESSULANA), was collected in 3 different locations in France to augment laboratory colonies and to conduct host specificity experiments. An eriophyid mite (yet to be identified) was discovered in southern France on French broom (GENISTA MONSPESSULANA). Stem galls were discovered on medusahead (TAENIATHERUM CAPUT-MEDUSAE) in Greece that have been tentatively identified as being created by the wasp EURYTOMA sp., based on molecular genetic analysis. The weevil, LARINUS FILIFORMIS, which is known to attack flowerheads of yellow starthistle (CENTAUREA SOLSTITIALIS) was collected in Bulgaria, and a colony was established in the EBCL quarantine laboratory. Exploration by BBCA cooperators for the eriophyid mite, ACERIA SALSOLAE, which is a prospective agent for Russian thistle (SALSOLA TRAGUS) was conducted in Greece, Italy, Bulgaria and Turkey. Mites were found at serveral sites in Turkey, and a laboratory colony was established at EBCL. In order to study the microbial diversity surrounding roots of the annual grass ventenata (VENTENATA DUBIA), soil was sampled (3 replicates + 3 controls) in France, Bulgaria, and Slovakia to compare the diversity of rhizoplan, rhizosphere, seed endophytes, and control soil. Under Objective 2a we made significant progress identifying the geographic origins of target weeds In order to direct where to look for prospective biological control agents, surveys were conducted to collect samples of several target weeds for molecular genetic analysis. Collections of the invasive grass, VENTENATA DUBIA, were made in France and central Europe, including at 17 populations from 6 different countries, including 3 countries new to the project (Serbia, Greece, Macedonia). Genetic analysis using allozymes and AFLP’s showed a match for a genotype in western Oregon with populations collected from Slovakia and Romania, and the most common genotype found in Idaho and eastern Oregon matched a population from Hungary. In addition, samples from southern Bulgaria have shown no match with any of the genotypes found in the U.S. Collections of medusahead (TAENIATHERUM CAPUT-MEDUSAE) have resulted in 5 new populations of the subsp. CRINITUM from 3 countries (Greece, Bulgaria, Macedonia). Populations of medusahead (TAENIATHERUM CAPUT-MEDUSAE), cheatgrass (BROMUS TECTORUM), and red brome (BROMUS RUBENS) were collected by a visiting ARS scientist and BBCA cooperators in 8 Eurasian countries. Seeds were germinated at EBCL, and DNA was extracted for genetic analysis. Samples of Sahara mustard (BRASSICA TOURNEFORTII) were collected in seven countries by EBCL and BBCA scientists in the Mediterranean region. Seeds were germinated in EBCL quarantine facility, and DNA was extracted and sent to cooperators at the University of California, Irvine for genetic analysis. Under Objective 2b we evaluated the genetic diversity of hoary cress (LEPIDIUM DRABA) and its associated root gall weevil (CEUTORHYNCHUS ASSIMILIS). The specialist lineage of the weevil which is considered as a prospective biocontrol agent of hoary cress, and the generalist lineage of the same species which develops on several Brassicaceae were analyzed using microsatellites. Results evidenced a gene flow between the specialist and the generalist when both populations co-occur that might represent an issue for release permission by TAG. Moreover, although a clear preference under choice and open field conditions by the specialist lineage for hoary cress was confirmed by CABI in collaboration with EBCL, the specialist was able to develop to adult on three federally listed threatened and endangered species. Taken as a whole, we believed that it will be difficult to get a release permit for the specialist lineage. Under Objective 2C we completed the population genetic analysis of yellow starthistle (CENTAUREA SOLSTITIALIS) sampled throughout the native range (France, Spain, Italy, Sicily, Greece, Bulgaria, and Turkey) in support of research being conducted in California to evaluate the effect of host plant genotype on efficacy of established biological control agents. The results indicate several genetically distinct populations occur in Europe, and that those from California are most similar to populations in Spain, France, Bulgaria and northern Greece. The stem-feeding shootfly (CRYPTONEVRA sp.), a prospective biocontrol agent of the giant reed (ARUNDO DONAX) in USA, has several genetic lineages, one of which can develop on native US common reed (PHRAGMITES AUSTRALIS). Several populations of the shootfly sampled in France by EBCL were analyzed by genetic sequencing to help determine if there is a genetic lineage that is specifically associated with ARUNDO DONAX. Under Objective 3a we conducted a field experiment with four conditions (hoary cress [LEPIDIUM DRABA] alone, hoary cress with the gall weevil (CEUTORHYNCHUS ASSIMILIS), hoary cress with the soilborne pathogenic fungus RHIZOCTONIA SOLANI, and all three organisms) was conducted at EBCL to measure possible interactions among the three organisms. Plant mortality rate tended to be higher in the weevil plus pathogen condition (21.8%) than in the weevil alone condition (13.8%), probably because the insect damage provides entry points for Rhizoctonia to attack the plant. Cultivatable bacteria were isolated from soil samples and screened against the 06f12 isolate of RHIZOCTONIA SOLANI used in the experiment. Three bacterial isolates were able to strongly inhibit the growth of RHIZOCTONIA SOLANI. 16S rRNA-gene-based metagenomics analysis showed that the relative abundance of the three bacterial inhibitors was similar (from 2 to 2.6%) in the different experimental conditions. This indicates that the introduction of Rhizoctonia solani did not increase the proportion of bacterial inhibitors. Real-time PCR used to quantify the natural and introduced populations of RHIZOCTONIA SOLANI in the metagenomic DNA extracted from the soil of the different conditions showed that Rhizoctonia populations did not vary significantly, mostly due to the presence of natural populations of Rhizoctonia in the rhizosphere of hoary cress. This also indicated that the introduced Rhizoctonia did not establish well in our experiment, thus explaining why the proportion of bacterial inhibitors did not differ among the four conditions. Analysis of the 16S rRNA gene sequences showed no significant modification of the community structure or diversity of bacterial populations by the four conditions. Under Objective 3b we made significant progress measuring the host plant specificity of the French broom weevil (LEPIDAPION ARGENTATUM), a prospective biological control agent of French broom (GENISTA MONSPESSULANA). Six nontarget lupine species endemic to California (LUPINUS BICOLOR, L. ARBOREUS, L. CHAMISSONNIS, L. PERENNIS, L. ALBIFRONS, L. MICROCARPUS) plus French broom (GENISTA MONSPESSULANA) controls were evaluated in no-choice host specificity tests. Eggs of the leaf-feeding moth, ABROSTOLA ASCLEPIADIS, a prospective biological control agent of swallow wort (VINCETOXICUM SPP.), were collected in northern France to perform a test on swallow wort. 116 larvae were used for a test in open conditions on 29 caged plants for obtaining pupae and a second generation during the summer period. An attempt to test the host specificty of the eriophyid mite, ACERIA SALSOLAE, a prospective biological control agent of Russian thistle (SALSOLA TRAGUS), in a field garden experiment with BBCA cooperators in Italy was abandoned because of the inability to collect sufficient numbers of the mite at previously recorded field locations in Greece.
1. Giant reed (ARUNDO DONAX) has invaded large areas of the western USA, where it blocks the flow of rivers, displaces native vegetation and impedes law enforcement along the Mexican border. Molecular genetic studies conducted at the European Biological Control Laboratory in Montpellier, France showed that the population of the shoot fly (CRYPTONEVRA SP.) that was being evaluated by ARS scientists at Mission, Texas develops on both giant reed and common reed (PHRAGMITES AUSTRALIS) in Europe, and therefore is probably not safe to use for biological control. However, other genetically distinct populations of the fly were found that may be specific to giant reed. This discovery was crucial for redirecting foreign exploration to discover a safe effective agent to control giant reed.
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