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Research Project: Discovery and Development of Biological Control Agents for Weeds that are Invasive in the U.S. and Native to Australia and Asia

Location: Office of International Research Engagement and Cooperation

2022 Annual Report

Objective 1: Discover, identify and initiate the development of new biological control agents for invasive weeds that are native to Australia and/or Asia such as Melaleuca, Lygodium, Acacia, Hydrilla, Nymphoides, Azolla and Rotala. Establish high-priority agents by collecting, rearing, and shipping to U.S. collaborators. (non-hypothesis driven) [NP304, C2, PS 2A 2B] Sub Objective 1.1. Discovery and identification of new biological control agents for invasive weeds and developing understanding of basic life history of natural enemies to design rearing methods and host range tests. Ship to U.S. collaborators. Sub Objective 1.2. Development of new biological control agents for invasive weeds. Conduct host specificity tests and assess impact of potential biological control agents. Objective 2: Develop an iterative approach in exploration for biological control agents using a decision process based on Next Generation Sequencing of weed targets in their native and introduced ranges and their natural enemies. (potentially hypothesis driven) [NP304, C2, PS 2B] Objective 3: Selection of biological control agents compatible with chemical and mechanical control or for areas where alternative controls of weed invasions are not feasible. (non-hypothesis driven) [NP304, C2, PS 2C]

Objective 1: Develop understanding of basic life history of natural enemies to design rearing methods and host range tests. Conduct host specificity tests and assess impact of potential biological control agents. Foreign exploration will be guided by the center of origin of the weed species (classical and molecular diagnostics), habitat diversity, climate matching, specific phenology and ecology of the targets. Sites for exploration will be identified through the use of herbarium records, local knowledge, and maps of ecological areas. Exploration will be conducted in a systematic manner visiting unique ecological areas in the distribution of targets. Sites will be surveyed at different times of the year, i.e. wet and dry seasons. Agents will be sought which supplement the modes of attack of agents already established in the U.S. Initial molecular screening with mitochondrial markers will be conducted on representative herbivore species collected and the weed target species to provide an indication of genetic diversity and structuring. For selected arthropods the number of life stages, feeding behavior, developmental time of immatures, sex ratio, oviposition behavior of adults, fecundity and adult longevity will be determined in the laboratory and supplemented with field observations. Preliminary host range tests will be designed to predict the field host range of a candidate biological control agents. Studies will also be undertaken to quantify the impact of promising agents for select target species. Objective 2: The prospective and iterative approach tests if provenance determination of the target weed can ensure there is no mismatch between areas of the native range surveyed for herbivores and the introduced ranges in terms of the target host plant. Provenance of the agent (controlling for cryptic species) is an important predictor of efficacy and host specificity of an agent. Objective 3: Investigation of existing data on the biology/host specificity/impact of natural enemies in large data sets will lead to the identification of specific traits that influence the compatibility of agents to produce increased efficiency where alternate or existing controls for target weeds are ineffective. Large data sets on the biology, impact and host specificity of insect herbivores as well as the phenology/demography have been accumulated for weed targets over past decades by our laboratory. Contrasting this information with the weed target’s preferred habitat/s in the invasive range, current success and application of alternative forms of control (chemical/mechanical) and areas where existing released biological control agents have been ineffective, will be used to guide prioritisation of the selection of new biological control agents to be evaluated in Australia or introduced into U.S. quarantine.

Progress Report
This is the Progress Report for the Specific Cooperative Agreement 58-0206-0-177-F which expires on December 30, 2024, entitled “Discovery and development of biological control agents for weeds that are invasive in the U.S. and native to Australia and Asia ” and Specific Cooperative Agreement 58-6032-2-002-F which expires on February 28, 2023, entitled “Biological Control of Weeds Endemic to Southeast Asia and Australia that are Invasive in the United States”. Objective 1. New biological control agents were evaluated in Australia for invasive weeds targeted for management in the United States. Earleaf acacia, Acacia auriculiformis (Fabaceae) is invasive in Florida, and evaluation of potential biocontrol agents of focused on two agents, the gall forming wasp, Trichilogaster sp., and tip binding Macrobathra moths. Seasonality surveys in north Queensland determined the gall wasp, Trichilogaster sp., was most abundant in Autumn and winter during the flowering/fruiting season. Another aim of these surveys was to locate new A. auriculiformis sites with the gall wasp and were located at Chillagoe, west of Cairns, in the limestone belt. Representative specimens from Chillagoe will be genetically characterized for comparison with existing specimens. The first shipment of this gall wasp was made to a quarantine facility in Fort Pierce in December 2021. Native range field surveys in northern Queensland and the Northern Territory provided data on how insect herbivores are responding to seasonal changes in their native habitat. Engagement with indigenous communities of the Tiwi Islands and Arnhem Land in the NT provided insect herbivore abundance data and rangers used supplied field survey kits and insect identification guides to independently carry out field surveys in very remote and inaccessible (to our staff) locations. Seasonal abundance data indicated the blotch miner and blister miner (Acrocercops sp.1 and 2), the flower gall cecid (Dasineura sp), and the seed-feeding weevil (Melanterius spp) were prevalent year-round while the leaf t tiers, Macrobathra spp., were abundant in Autumn. Greenhouse and laboratory experiments monitoring the efficacy and host specificity of Trichilogaster sp. nov. and Macrobathra callipetala. Assessment of the impacts of the gall wasp indicate it significantly reduces the growth of acacia seedlings. Objective 2. Progress was made to develop an iterative approach to explore for biological control agents in their native and introduced ranges using a decision process based on Next Generation Sequencing of weed targets and their natural enemies. Genomics expertise was brought in house through the employment of a translational genomics scientist. Collaborative efforts remain and are shared across three laboratories, the USDA ARS Australian Biological Control Laboratory, the USDA ARS Invasive Plant Research Laboratory and the University of Queensland. Samples of the Trichilogaster wasp were collected from throughout its native range in Australia and preliminary analyses have been undertaken to validate genetic characterization. Similar studies were undertaken for Hydrellia leaf mining flies on hydrilla, and results indicate that there are at least two genotypes of these flies in Australia that could be evaluated separately as biological control agents. Original studies and US releases were performed on the basis that only one species existed. Objective 3. Investigation of hydrilla datasets accumulated since the mid-1980s identified gaps in the geographic surveys for biological control agents of hydrilla, Hydrilla verticillata in Australia. There is potential to explore for cold tolerant herbivores in temperate regions that could be suitable for use in the northern U.S. where hydrilla is problematic and where existing agents don’t overwinter. These surveys were initiated but follow up herbivore collection surveys this year were hindered by severe record flooding of aquatic environments in southern temperate Australia. Interrogation of historic hydrilla collection data and field preserved specimens has identified that there is potential to evaluate the biogeography of hydrilla reproductive biotypes and the genetic phylogenies of hydrilla and associated leaf-mining Hydrellia flies. This has been pursued with preliminary results identifying potential leaf mining Hydrellia flies for evaluation (see Objective 2 above). Molecular techniques are being developed for the hydrilla plant molecular diagnostics in collaboration with Texas Christian University and the US Army Corps of Engineers, Engineer Research and Development Center.

1. Advanced genetic tools correct the origin of introduction of invasive old world climbing fern in Florida. Old world climbing fern is highly invasive in Florida where it smothers native vegetation, promotes the spread of wildfires and damages ecosystems, particularly in the Florida Everglades. Natural controls are need in these pristine environments. It’s thought that the most specific and damaging biological control agents are found from where invasive weeds originated. The origins of Florida old world climbing fern was initially thought to be Cape York in tropical North Queensland, Australia and plant feeding mites from this location were introduced into Florida to control this fern, but their impacts were sporadic. Recent advanced genetic techniques determined that the origin of introduction is likely to be the western Pacific or south-east Asia not Australia, and mites and other plant feeding insects from this region will now be evaluated as natural controls.

2. Biological control agent specific against the weed earleaf Acacia exported to stateside quarantine. Biological control agents are urgently required for earleaf Acacia, Acacia auriculiformis, an Australian native tree invasive in Florida. Without control this invasive tree could rapidly expand, reducing biodiversity by invading protected areas such as the Everglades National Park. A damaging gall-forming wasp, Trichilogaster sp. was prioritised for evaluation as a biological control agent as closely related species have successfully controlled Acacia spp. in Africa. Preliminary no-choice host range testing and impact assessments have been completed and determined that this wasp is highly specific and damaging to seedlings. This potential biological control agent was sent to U.S. quarantine for final testing.