Location: European Biological Control Laboratory
2024 Annual Report
Objectives
Objective 1: Explore for natural enemies, primarily arthropods, 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 Sahara mustard, French broom, annual grasses, stinkwort, tree of heaven and swallow-worts.
Objective 2: Perform taxonomic, population genetic, and phylogeographic studies of target weeds and biological control agents to better understand the origin of invasive populations, arthropod-plant relationships, and clarify species.
• Sub-objective 2A Phylogeography of Sahara mustard, stinkwort, ventenata.
• Sub-objective 2B Genetic characterization of potential biocontrol agents.
Objective 3: Identify the biological, physical and chemical parameters that affect the efficacy, specificity, and safety of biological control agents, and those underlying the interactions between target weeds, biological control agents, and the environment.
• Sub-objective 3A Assess the potential host specificity on selected plant species, focusing on host use of candidate agents for tree of heaven, stinkwort, swallow-worts, medusahead and Sahara mustard.
• Sub-objective 3B Investigate foraging behavior and impact of biological control agents with French broom weevil and French broom psyllid.
• Sub-objective 3C Investigate safety procedures of biological control agents, including French broom arthropod candidates and other potential biological control agents.
• Sub-objective 3D Compare the impact of rhizospheric bacteria and fungi from native and invasive ranges on the fitness of the annual grass weed ventenata.
Approach
The goal of this current 5-year plan is to conduct a customer-driven research program that will enhance our ability to manage invasive weeds in the U.S. Successful alien weeds usually lack natural enemies, which control them in their native ranges. The European Biological Control Laboratory research team and associated cooperators will accomplish this by using a combination of hypothesis and goal-driven research toward the discovery and development of exotic natural enemies for classical (=importation) biological control of alien weeds in the U.S. The long-term research plan will lead to environmentally safe and sustainable management of weeds that threaten U.S. agriculture and natural ecosystems over large areas. The process usually involves three phases that can be conducted in parallel: 1) exploration to discover and characterize candidate arthropod biological control agents and their target host plants in full compliance with current regulations in host countries regarding exportation of live organisms and benefit-sharing, 2) morphological and genetic characterization of the field collected arthropod material and related natural enemies, and 3) evaluation of the host specificity and effectiveness of the best selected candidate biological control agents. Candidates that are found to be safe and effective are then proposed for release in the U.S., and must undergo a rigorous review and permitting process involving state and federal agencies. Research on Sahara mustard, French broom, annual grasses, tree of heaven and swallow-worts 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 in classical biological control is highly cost effective, and critical to achieving ecologically rational, sustainable management of some of the most important invasive weeds in the United States.
Progress Report
Objective 1: For stinkwort (Dittrichia graveolens), a total of 37 pupae and larvae of the promising moth Condica viscosa were collected in Cyprus. A rust was also collected in Cyprus, which has not been identified to date. For cogongrass, an unidentified smut fungus was reported and collected from Spain and Portugal. This systemic smut attacks the flower clusters leading to no seed production. The host specific chrysomelid beetle, Chrysochus asclepiadeus was collected from swallow-wort plants in the field prior to shipping to collaborators in the United States.
Objective 1: Medusahead (Taeniatherum caput-medusae) is one of the invasive grasses of the United States with Eurasian origin. A newly described Eurytomidae wasp (Tetramesa amica) is a promising biocontrol agent against medusahead. Since there is no information available on the biology of the insect and its two parasitoids, regular biweekly samplings were done in four locations in northeast Greece where Tetramesa was discovered. With the information gathered from this study, and further host specificity tests, there is hope to be able to utilize this gall wasp for biological control of medusahead in the United States.
Objective 1: Sahara mustard (Brassica tournefortii) is an important invasive weed in California. Surveys in Israel to search for natural enemies for this weed had begun, but have now been suspended in Israel due to the current conflict in the region. However, the United Arab Emirates was selected as an alternative country to survey. As it seems the presence or absence of the weed is highly dependent on the rainfall and since this was a very dry year for the region, plants in only in two locations could be collected. No insects emerged from the collected material. In one location larvae of Diamond back moth (Plutella xylostella) was collected and the adults were kept in ethanol for further study.
Sub-objective 2A: The genetic analysis of individual stinkwort plants representing the invaded range was pursued by using the population genetic markers (microsatellites markers) developed in previous years. In total, DNA extracted from 90 individual samples representing 13 sites across California were processed. Population genetic data of these populations were combined with those obtained from last year. Genetic analysis based on a total of 194 stinkwort plants showed that the level of genetic diversity of stinkwort is very low in California and that stinkwort exists in two genotypes in California, which are differently distributed between the North and South of the state. These genotypes have not yet been identified in the Mediterranean Basin in the native range.
Sub-Objective 2B: DNA barcoding was used to identify natural enemies of stinkwort collected from Crete and Cyprus, resultng in the identification of two foliage feeder moths, Heliothis peltigera and Helicoverpa armigera, three scentless plant bugs Stictopleurus sp., Liorhyssus hyalinatus and Corizus Hyoscyami, and one plume moth, Hellinsia sp. All are considered non-specific to stinkwort, so it is unlikely that they will be retained as prospective biocontrol agents for release in California.
Sub-Objective 2B: Genetic analysis of the candidate agent, Condica viscosa for biocontrol of stinkwort confirmed that populations collected in Cyprus in 2021 and 2023 belong to a single species, hence preventing the risk of unintentional introductions of another species in quarantine testing and ultimately into the United States.
Sub-Objective 2B: A DNA barcoding approach was applied to natural enemies associated with Sahara mustard collected from Israel and Egypt, resulting in identification of two leaf mining flies (Ocnogyna clathrata and Chromatomyia horticola) and the stem miner, Ceutorhynchus pallidactylus. All are considered nonspecific to Sahara mustard, so it is unlikely that they will be retained as prospective biocontrol agents for release in California.
Subobjective 2B: A smut has been collected in Spain on cogongrass (Imperata cylindrica). Molecular and phylogenetic analysis revealed that this fungus belongs to the Sporisorium genus.
Sub Objective 2B: A rust has been collected in Cyprus and Portugal on stinkwort (Dittrichia graveolens). Molecular and phylogenetic analysis revealed that this fungus is Coleosporium inulae. ITS sequences have been submitted to GenBank under accession numbers PP574452-PP574453.
Sub Objective 3A: Twenty-five plant species, closely related to stinkwort, including U.S. natives, crop species (sunflower), and ornamentals (tagetes) were tested with the potential moth candidate to narrow down the moth host range.
Sub Objective 2A: For tree of heaven (ToH), the eriophyid mite, Aculus taihangensis was reared by researchers in Montpellier, France, and augmentatively released in three experimental sites (+2 controls) in France. An integrated approach of controlling tree of heaven by using mechanical method (debarking) and augmentative biocontrol was pursued. Field inoculated ToH plants exhibited mite symptoms earlier that naturally infected ToH.
Sub Objective 3D: Soil from the United States, where the dominant genotype of the invasive grass Ventenata dubia occurs was collected in August 2023. Seed germination assays and transplant experiments were started in October 2024. DNA extraction from soil collected in the native and invasive ranges were performed at the beginning of the experiement. Monitoring of growth, flowering, and mortality is still ongoing. Isolation and characterization of microbes and analysis of microbial community composition will be performed at the end of the life cycle of the plant.
Accomplishments
1. Large-scale host specificity tests for stinkwort. Stinkwort is an exotic plant species damaging natural habitats in California. Foreign exploration was conducted on several Mediterranean islands for host specific natural enemies. A moth was selected and tested on over 25 different plant species (U.S. natives and crops) at the quarantine facility in Montpellier, France. Laboratory tests revealed a very limited herbivory outside the genus of the target weed, which is very promising for future open field tests.
