Research Project: Biological Control of Invasive Pests in Agroecosystems and Wetland, Forest and Rangeland Ecosystems in the Far Western U.S.

Location: Invasive Species and Pollinator Health

2025 Annual Report

Objectives
1) Discover, identify and prioritize the development of new biological control agents for targeted invasive weed and arthropod pests such as medusahead and bagrada bug. Sub-objective 1A: Determine point(s) of origin of ice plant. Sub-objective 1B: Discover, identify, and prioritize candidate agents of cheatgrass, medusahead and ice-plant. Sub-objective 1C: Discover, identify and prioritize candidate agents of bagrada bug. 2) Evaluate the host range, biology, and potential efficacy of prospective biological control agents for weed and arthropod pests such as French broom and bagrada bug. Sub-objective 2A: Deleted. Sub-objective 2B: Evaluate host range, biology and potential efficacy of candidate agents on yellow starthistle, Russian thistle, French broom, cheatgrass, medusahead, ice plant, and arundo. Sub-objective 2C: Evaluate host range, biology and potential efficacy of candidate biocontrol agents of bagrada bug. 3) Release permitted biological control agents targeting terrestrial weed and arthropod pest targets such as yellow starthistle, Cape-ivy, and spotted wing drosophila, and determine their establishment, dispersal, efficacy, influence on pest populations, benefits for native plant communities or crops, and suitability for integration into integrated weed and arthropod pest management plans. Sub-objective 3A: Rear, release and evaluate a new biological control agent of yellow starthistle. Sub-objective 3B: Release and evaluate biological control agents on bagrada bug and spotted-wing drosophila. Sub-objective 3C: Examine ecological impacts of Cape-ivy biocontrol and implications for integrated management.

Approach
Under Objective 1, we will determine the origin of crystalline ice-plant by sampling the invaded range in California and native ranges in South Africa and Mediterranean Europe. Genetic analyses will involve chloroplast and nuclear DNA. We will isolate soil microbes associated with medusahead and cheatgrass and determine best candidates. Surveys will be conducted in California, Nevada and Oregon and will include determination of symptoms and culturing. We will survey crystalline ice plant in South Africa and the Mediterranean and determine best candidate agents on the basis of host specificity and ability to reduce growth and reproduction. We will identify and prioritize candidate agents of bagrada bug that can attack eggs through surveys in South Africa and Kenya. Under Objective 2, we will determine the host specificity and efficacy of one candidate agent each targeting yellow starthistle, Russian thistle and French broom. We hypothesize that these agents will develop and reproduce only on the targeted weed. Biological safety will be examined in no-choice and choice tests. Candidate impact on plant biomass and seed production will be examined in quarantine and in the native range. We will quantify the host range and efficacy of candidate agents of medusahead and cheatgrass. Microbial candidates will be evaluated for inhibition of root development or seed germination. Insects or mites will be evaluated for ability to reduce growth and reproduction. We hypothesize that one host-specific and efficacious agent of crystalline ice plant will be found. We will conduct host range and efficacy tests as for other weeds. We hypothesize that the arundo leafminer can be reared on a California isolate of its fungal associate. We will isolate the leafminer from its native fungal isolate and parasitic nematode. We will assess host specificity of two candidate parasitic wasp species targeting bagrada bug eggs by comparing attack on native plant bugs and the pest, and ability to kill eggs. Under Objective 3, we will increase production of a newly-permitted rosette-feeding weevil for biological control of yellow starthistle. We will develop an artificial diet to facilitate mass-rearing and refine plant-based rearing. We hypothesize that this weevil will establish on and negatively impact yellow starthistle. Releases will be performed in the coastal hills, Central Valley, and Sierra foothills. We will assess field attack rates by resident enemies on bagrada bug eggs by attracting native natural enemies, and cameras and traps will be used to identify species. Searches will also be made for a non-native natural enemy that may already be present. We will release the first permitted biocontrol agent targeting spotted-wing drosophila in the U.S. and will verify establishment and efficacy. If the new enemy fails to establish, we will study native enemies. We hypothesize that the Cape-ivy shoot tip-galling fly will reduce density and flowering of this weed and increase native plant diversity. Biocontrol will be integrated with physical removal. Where the fly fails to establish, we will release a leaf-mining moth.

Progress Report
This is the final report for project 2030-22000-033-000D, “Biological Control of Invasive Pests in Agroecosystems and Wetland, Forest and Rangeland Ecosystems in the Far Western U.S.”, which is currently under OSQR review. For additional information, see the new project report once it has completed the OSQR certification process. The following research was carried out in support of Objective 1: Discover, identify and prioritize the development of new biological control agents for targeted invasive weed and arthropod pests such as medusahead and bagrada bug. Invasive ice plants smother native plants and alter soil quality. For Sub-objective 1A, an ARS entomologist in Albany, California, sampled crystalline and slenderleaf ice plants along the California coast, and cooperators in South Africa performed genetic analyses on invasive and native range samples. Results indicate coastal western South Africa as the area of origin of both invasive ice plant species in California, with samples from Spain being closely related. In addition, a stem-boring weevil on crystalline ice plant and larvae of several moth species on slenderleaf ice plant were collected and studied in South Africa by an ARS researcher. A root-feeding weevil was studied on slenderleaf ice plant in Spain by an Italian cooperator. Cheatgrass and medusahead are major invasive annual grasses in arid western U.S rangelands, consuming water, degrading forage quality and fueling wildfires. Under Sub-objective 1B, an ARS microbiologist in Albany, California, sampled the root zone of cheatgrass and a sympatric native perennial grass for three years across the western United States. Genetic analyses of bacteria, fungi, and other microbes are in progress and completed for the first of three years of samples. Cultures of a soil bacterium were genetically characterized, and their herbicidal effects were found to be minimal. An ARS entomologist shipped rust-infested cheatgrass samples from Greece to ARS collaborators in Frederick, Maryland. Bagrada bug has invaded California’s $2.3 billion-per-year cole-crop industry. This stinkbug feeds and spreads on related non-native weeds and native plants. In support of Sub-objective 1C, an ARS entomologist in Albany, California, produced sterile sentinel eggs from unmated bagrada bug females to use as bait for field collection of parasitic wasps. Parasitism of seven-day-old sterile eggs did not differ from fresh, fertilized eggs, which attract wasps for only three to four days. In addition, parasitism of 12-day-old sentinel eggs treated with X-rays was slightly lower than on fresh eggs. These results show that irradiated sentinel eggs may facilitate foreign exploration for bagrada bug parasites, including new sites identified in South Africa and Italy. The following research was carried out in support of Objective 2: Evaluate the host range, biology, and potential efficacy of prospective biological control agents for weed and arthropod pests such as French broom and bagrada bug. Yellow starthistle (YST) consumes water, displaces native plants, and hinders grazing and outdoor activities, including military training, in the western United States. Under Sub-objective 2B, a seed-feeding weevil was collected in Bulgaria in June 2023 by an ARS entomologist and European collaborators and imported into the ARS quarantine laboratory in Albany, California. Mated females were confined on flowering YST and four closely related non-target native plants. While weevils fed and laid eggs on YST and larvae developed within YST seedheads, only one non-target species flower bud was damaged by weevil feeding, zero eggs were laid, and no larval development occurred on the native plant species tested. A petition to permit release of this weevil is in preparation. Russian thistles displace native plants in western U.S. rangelands, obstruct roads, consume water, and fuel wildfires. Also, under Sub-objective 2B, ARS entomologists in Montferrier-sur-Lez, France, sent 200 pupae of a leaf- and flower-feeding moth to the ARS quarantine laboratory in Albany, California, where mated female moths were confined on five Russian thistle species and on seven non-target plant species. Three Russian thistles supported full development, while no eggs or larval development occurred on non-target plants. Hatched larvae were placed on four Russian thistles and five non-targets; larval damage and growth were observed on all Russian thistles, while no sustained damage or development occurred on non-targets. A petition to permit release of this moth is in preparation. French broom invades woodlands, pastures and meadows in the Pacific U.S. states, displacing native flora and fueling wildfires. Also, in support of Sub-objective 2B, an ARS entomologist in Albany, California, confined females of a shoot-galling and seed-feeding weevil on French broom or five native plant relatives known as lupines in an ARS quarantine laboratory in Albany, California. Abundant galls formed on French broom while none formed on the non-target lupines. Seed-feeding tests of the weevil on French broom and non-target plant species will be conducted in France. For Sub-objective 2B, native microbes were tested by an ARS microbiologist in Albany, California, as candidate biological control agents targeting medusahead and cheatgrass. Bacteria were isolated from soils, genetically characterized, and tests of their effects on grass seed germination are ongoing. Fungi were isolated from inside cheatgrass and medusahead seeds and their DNA analyzed. Tests of interactions between these seed bacteria and fungi are ongoing. An ARS entomologist from Albany, California, oversaw studies of mite and midge candidate biocontrol agents on cheatgrass and medusahead by collaborators in Greece, Bulgaria, and Serbia, and imported weevils collected from cheatgrass and medusahead in Greece into the ARS quarantine laboratory in Albany, California, where host-range and genetic studies are ongoing. Also, in support of Sub-objective 2B, a stem-boring weevil imported from South Africa was tested by an ARS entomologist in Albany, California, on crystalline ice plant and two U.S. native members of the same plant family (Aizoaceae) in quarantine. Weevils were successfully reared on ice plants, while no development or reproduction occurred on non-target plants. Further tests are ongoing.

Accomplishments
1. Development of novel methods for sampling parasitic wasps attacking stinkbug eggs in the field. Parasitic wasps that attack stinkbug eggs are often used as biocontrol agents of these key pests of crops. Detection of these wasps, including both monitoring of released wasps and discovery of previously unknown wasp species that could become new biocontrol agents, is often achieved by deploying lab-reared stinkbug eggs in the field as sentinels. ARS researchers in Albany, California, developed two novel methods for obtaining sterile bagrada bug eggs for field monitoring of parasitic wasps: inducing oviposition from unfertilized females and treating fertilized eggs with x-rays. Sterile eggs remained attractive to wasps longer than untreated, fertilized eggs and come with no risk of accidental release of the stinkbug pest in a monitored area. To our knowledge, this is the first study to demonstrate the feasibility of using unfertilized or x-ray treated stinkbug eggs as sentinel eggs for parasitic wasp monitoring and discovery. These new methods improve the precision and safety of monitoring wasps attacking stinkbugs and accelerate the discovery and development of new biocontrol agents for these important crop pests.

Review Publications
Hougardy, E.H., Haff, R.P., Hogg, B.N. 2024. Improving the efficiency and safety of sentinel stink bug eggs using X-rays. Insects. 15(10). Article 767. https://doi.org/10.3390/insects15100767.
Hogg, B.N., Daane, K.M. 2024. Landscape effects on seasonal abundance of Drosophila suzukii and its parasitoids in California cane berry fields. Agricultural and Forest Entomology. 27(2):304-315. https://doi.org/10.1111/afe.12664.
Lisi, F., Biondi, A., Hogg, B.N., Rossi-Stacconi, M., Wang, X., Daane, K.M. 2024. Cold storage of Ganaspis kimorum (Hymenoptera: Figitidae) immature stages for optimized classical biological control of Drosophila suzukii (Diptera: Drosophilidae). Journal of Economic Entomology. Article toae286. https://doi.org/10.1093/jee/toae286.
Lisi, F., Rogers, V.D., Henry, E.E., Hogg, B.N., Biondi, A., Wang, X., Daane, K.M. 2025. Potential interactions of larval and pupal drosophila parasitoids and their implications for biological control of Drosophila suzukii. Biological Control. 204. Article 105756. https://doi.org/10.1016/j.biocontrol.2025.105756.
Goemann, H.M., Ulrich, D.E., Peyton, B.M., Gallegos-Graves, L., Mueller, R.C. 2024. Severe and mild drought cause distinct phylogenetically linked shifts in the blue grama (Bouteloua gracilis) rhizobiome. Frontiers in Microbiomes. 2. Article 1310790. https://doi.org/10.3389/frmbi.2023.1310790.
Lazarus, B.E., Mueller, R.C., Germino, M.J. 2025. Soil-microbial communities respond less than plant communities to synthetic- or bio-herbicides applied to address the exotic grass-fire cycle in rangelands. Science of the Total Environment. 991. Article 179831. https://doi.org/10.1016/j.scitotenv.2025.179831.
Moran, P.J., Rogers, D.V., Bitume, E.V., Portman, S.L., Goolsby, J.A. 2025. Establishment and dispersal of the armored scale Rhizaspidiotus donacis for biological control of Arundo donax in northern California. Biocontrol Science and Technology. 35(7):755-776. https://doi.org/10.1080/09583157.2025.2514451.
Daane, K., Hogg, B.N., Stahl, J.M., Haviland, D.R., Wang, X. 2025. Naturally occurring parasitoids of Drosophila suzukii (Diptera: Drosophilidae) and other drosophilids in California. Journal of Economic Entomology. Article toaf132.. https://doi.org/10.1093/jee/toaf132.
Hougardy, E.H., Rogers, D., Hogg, B.N. 2025. Foraging abilities and competitive interactions between two egg parasitoids of bagrada bug in California. Bulletin of Entomological Research. 114(6):737-743. https://doi.org/10.1017/S0007485324000531.