Location: Invasive Species and Pollinator Health
2024 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 report documents progress for project 2030-22000-033-000D, titled, “Biological Control of Invasive Pests in Agroecosystems and Wetland, Forest and Rangeland Ecosystems in the Far Western U.S.”, which started in May 2021.
Cheatgrass and medusahead are major invasive annual grasses in arid western U.S rangelands, consuming water, degrading forage quality and fueling wildfires. In support of Sub-objective 1B, an ARS scientist in Albany, California, completed the third year of biogeographical sampling of the soil ‘rhizosphere’ (root zone) of cheatgrass and a co-occurring native perennial grass. Sequencing of molecular markers for bacteria, fungi, and other microbes were completed for the first year and DNA extractions and analyses are ongoing for subsequent years.
Also under Sub-objective 1B, an ARS scientist in Albany, California, visited South Africa to examine and collect the stem-boring weevil Lixus carinerostris, a candidate agent for crystalline ice plant. On slenderleaf ice plant, larvae of several moth species found feeding on flowers are being identified. Additional fieldwork examined candidate agent biology, host range, and efficacy. A root-feeding weevil, Temnorhinus mixtus, was studied on slenderleaf ice plant in the Canary Islands by an Italian cooperator.
Bagrada bug has invaded California’s $2.3 billion-per-year cole crop industry (for example, cabbage, broccoli, and cauliflower). This stinkbug feeds and spreads on related non-native weeds and native plants. In support of Sub-objective 1C, in October 2023, Crete and Cyprus were explored to collect bagrada bug and its natural enemies but none were found. Tests were conducted using X-rays to lengthen the longevity of ‘sentinel’ bagrada bug eggs placed in the field for collection of parasitic wasps, as fresh eggs attract wasps for only 3-4 days. Parasitism levels on 12 day-old irradiated eggs were only slightly lower than on fresh eggs. These results show that use of irradiated eggs may facilitate foreign exploration for bagrada bug parasites.
Candidate biological control agents of weeds and pest insects must be evaluated in a quarantine laboratory and, when possible, in the native range, to determine their host range (safety), biological life cycle and efficacy. These studies were completed under Objective 2.
Yellow starthistle (YST) consumes water, displaces native plants and hinders grazing in the western United States. In support of Sub-objective 2B, a seedhead-feeding weevil (Larinus filiformis) was collected in Bulgaria in June 2023 by an ARS scientist and Serbian and Bulgarian collaborators and imported into the ARS quarantine laboratory in Albany, California. Egg-laying 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 on seedheads, only one non-target species (Cirsium hydrophilum) flower bud was damaged by weevil feeding, zero eggs were laid, and no larval development occurred on the native plant species tested.
Russian thistles displace native plants in western U.S. rangelands, obstruct roads, consume water, and fuel wildfires. In support of Sub-objective 2B, 200 pupae of the leaf- and flower-feeding moth Gymnancyla canella were collected in southern France by cooperators at the ARS-European Biological Control Laboratory (EBCL) and sent to an ARS scientist in Albany, California. Egg-laying females were confined in quarantine on Russian thistles, including Salsola australis, S. kali, S. ryanii, S. soda, and S. tragus, or on seven non-target plants. Three Russian thistle species (S. kali, S. soda, and S. tragus) supported full development, while no egg-laying or larval development occurred on non-target plants. In separate tests, newly hatched larvae were placed on four Russian thistles or five non-targets. Larval damage and development were observed on all Russian thistles while no sustained damage and no development occurred on non-targets.
French broom invades woodlands, pastures and meadows in the Pacific U.S. states, displacing native flora and fueling wildfires. In support of Sub-objective 2B, an ARS scientist in Albany, California, confined females of the shoot-galling and seed-feeding weevil Lepidapion argentatum in quarantine on French broom or five native plant relatives known as lupines. Abundant galls formed on French broom but none formed on the non-target lupines.
In support of Sub-objective 2B, native microbes were evaluated by an ARS scientist in Albany, California, as biological control agents targeting medusahead and cheatgrass. Cultures of bacteria (Pseudomonas) were isolated from soils collected under Sub-objective 1B and characterized using sequencing of the full-length 16S rRNA gene. Tests of their efficacy as pre-emergent bioherbicides against cheatgrass, medusahead and native grass seeds are ongoing. Fungal seed endophytes (living inside the seed) were isolated from cheatgrass and medusahead and sequenced, and tests of antagonistic interactions between Pseudomonas and endophytes are ongoing. Another ARS scientist in Albany, California, and collaborators conducted field surveys in Greece, Bulgaria, and Serbia to collect insects and mites on annual grass weeds.
Also, under Sub-objective 2B, the stem-boring weevil Lixus carinerostris was tested by an ARS scientist in Albany, California, on crystalline ice plant and two U.S. native members of the same plant family (Aizoaceae) in quarantine. Weevils were reared on ice plant, while no development or reproduction occurred on non-target plants.
Arundo consumes water and fuels wildfires in the southwestern United States. Under Sub-objective 2B, the leafminer Lasioptera donacis was reared for three generations in quarantine by an ARS scientist in Albany, California. Preserved females were sent to the EBCL to verify that a nematode that can cause disease in the leafminer has been excluded. Exposure of leafminers to fungi isolated from arundo leaf sheaths from California and DNA tests showed that the leafminer is able to use the California fungi as a food source.
In support of Sub-objective 2C, an ARS scientist in Albany, California, conducted studies on host range of exotic candidate natural enemies of bagrada bug. Data from past years was compiled and analyzed, and it was found that the parasitic wasp Gryon aetherium parasitized 10 out of the 14 tested non-target species, although parasitism levels were less than 1% on three and more than 30% on only two. Choice tests showed that G. aetherium preferred bagrada bug eggs.
Once permits are received for field release, new biological control agents must be released and evaluated for field establishment, dispersal, and efficacy. These studies were conducted under Objective 3.
In support of Sub-objective 3A, rearing of the YST rosette- and taproot-feeding weevil Ceratapion basicorne continued and two release sites were monitored by an ARS scientist in Albany, California. Between 1% and 3% of roots sampled in June 2024 showed signs of infestation, indicating establishment at both sites. Roots of YST from Greece imported into quarantine yielded 18 adult weevils to start new colonies. Rearing has been interrupted by the discovery of infection, in some imported weevils, by an unknown microbe (Rickettsia sp.), that may prevent infected females from producing live male offspring. Efforts are underway to develop protocols to distinguish infected and healthy adults using molecular methods without killing weevils. Imported weevils will thus be screened and infected adults removed.
In support of Sub-objective 3B, an ARS scientist in Albany, California, analyzed field data on parasitism of bagrada bug eggs in California. Only 8% of the 49,488 eggs collected in 2021 and 2022 were parasitized by the adventive wasp Gryon aetherium (introduced accidentally through unknown means), although parasitism exceeded 20% at some sites, and less than 1% of eggs were parasitized by a native wasp, Ooencyrtus californicus. The efficacy of G. aetherium in parasitizing bagrada bug eggs was compared to O. californicus in laboratory tests. G. aetherium attacked eggs in soil, where bagrada bug lays most of its eggs, while O. californicus did not. Parasitism rates by G. aetherium were also far higher than O. californicus.
Spotted-wing drosophila (SWD), a fruit-feeding fly, is a major invasive pest of blueberries, blackberries, raspberries, strawberries, and cherries in California, threatening a $3.4B crop industry. In support of Sub-objective 3B, 1,200 adult wasps of Ganaspis kimorum, a new exotic parasitic biological control agent, were released in an organic raspberry field in Watsonville, California. Traps baited with SWD larvae and collections of berries were used to monitor establishment and dispersal across 250 acres of berry fields and semi-natural habitats. Releases and monitoring were also conducted at six smaller sites. The wasp was recovered at two sites.
Cape-ivy invades forests and scrublands along the California coast. In support of Sub-objective 3C, an ARS scientist in Albany, California, verified establishment of the shoot-tip galling fly Parafreutreta regalis at nine sites. A second year of studies of fly impact on Cape-ivy was completed at three sites. A study of integrated herbicide + biological control was limited by dense populations of other weeds which smothered Cape-ivy, obscuring effects of the fly to limit regrowth.
Accomplishments
1. Shoot-tip galling fly established for biological control of Cape-ivy. Cape-ivy is a perennial vine that smothers shrubs and trees and obstructs creeks in forests and grassland/scrub habitats along the coast of California, threatening water resources and reducing plant diversity. ARS scientists in Albany, California, released a shoot-tip galling fly (Parafreutreta regalis) that was permitted by the USDA as a result of prior ARS research showing it was safe for release. Female flies lay eggs in shoot tips causing tumor-like galls to form, and larvae feed inside the gall. The fly was released initially in cages with adults, but to avoid the risk of cage loss or damage, an innovative approach was developed in which groups of greenhouse-galled plants were placed at field sites and adults allowed to emerge. Surveys starting in 2021 verified establishment at ten sites, including sites on public parkland, with gall densities as high as 70 per square meter (8 per square foot) and dispersal up to 2 miles. Galls were found throughout the year for three years. Knowledge of establishment is now guiding studies of fly impact. Stakeholders have requested site visits to check for the fly on their lands.
2. Field establishment of a biological control agent on yellow starthistle. Yellow starthistle (YST) is an annual weed from Eurasia that has become invasive on more than 10 million acres in the western U.S. It outcompetes native flora, is poisonous to horses, and produces stout, sharp spines that degrade recreational opportunities on public lands and interfere with training exercises on military bases. Ceratapion basicorne, a weevil that mines in the crown and taproot of YST, was developed by ARS scientists in Albany, California, as a biocontrol agent and released at two sites in El Dorado and Monterey counties in California, in 2021 and 2022, respectively. Dissection of 200 YST roots collected from each of the two release sites in June 2024 revealed evidence of C. basicorne damage in 3% of roots from the El Dorado County site and 1% of roots from the Monterey County site, indicating that this agent is successfully colonizing YST plants in these two disparate habitats. Annual field monitoring will continue to track weevil establishment at these sites, while mass-rearing efforts by four stakeholders, coordinated by ARS scientists in Albany, California, will support additional weevil releases across the western United States, representing a new, sustainable, low-cost tool for YST management.
Review Publications
Sarratt, J.V., Perryman, M., Pratt, P.D. 2023. Galls formed by Aceria genistae (Acari: Eriophyidae) alter reproduction of the invasive weed Scotch broom (Cytisus scoparius) in the USA. Biocontrol Science and Technology. 33(9):805-819. https://doi.org/10.1080/09583157.2023.2245984.
Winston, R.L., Schwarzlander, M., Hinz, H.L., Pratt, P.D. 2024. Prioritizing weeds for biological control development in the western USA: Adaption of the biological control target selection system. BioControl. 69:335–351. https://doi.org/10.1007/s10526-024-10243-8.
Azrag, A.G., Obala, F., Tonnang, H.E., Hogg, B.N., Ndlela, S., Mohamed, S.A. 2023. Predicting the impact of climate change on the potential distribution of the invasive tomato pinworm Phthorimaea absoluta (Meyrick) (Lepidoptera: Gelechiidae). Scientific Reports. 13. Article 16477. https://doi.org/10.1038/s41598-023-43564-2.
Hogg, B.N., Grettenberger, I.M., Borkent, C.J. 2023. Parasitism by Gryon aetherium (Hymenoptera: Scelionidae) on Bagrada hilaris (Hemiptera: Pentatomidae) eggs in northcentral California. Journal of Economic Entomology. 116(5):1540–1550. https://doi.org/10.1093/jee/toad172.
Bitume, E.V., Rogers, V.D., Pratt, P.D., Goolsby, J., Moran, P.J. 2024. Establishment of the wasp Tetramesa romana for biological control of Arundo donax in northern California and the role of release plot manipulation. Biological Control. 192. Article 105489. https://doi.org/10.1016/j.biocontrol.2024.105489.
Gariepy, T.D., Abram, P.K., Adams, C., Beal, D., Beers, E., Beetle, J., Biddinger, D., Brind’Amour, G., Bruin, A., Buffington, M.L., Burrack, H., Daane, K., Demchak, K., Fanning, P., Gillett, A., Hamby, K., Hoelmer, K., Hogg, B.N., Isaacs, R., Johnson, B., Lee, J.C., Levensen, H., Loeb, G., Lovero, A., Milnes, J., Park, K., Prade, P., Regan, K., Renkema, J., Rodriguez-Saon, C., Neupane, S., Jones, C., Sial, A., Smythman, P., Stout, A.R., Van Timmeren, S., Walton, V.M., Wilson, J., Wang, X. 2024. Widespread establishment of adventive populations of Leptopilina japonica (Hymenoptera, Figitidae) in North America and development of a multiplex PCR assay to identify key parasitoids of Drosophila suzukii (Diptera, Drosophilidae). NeoBiota. 93:63–90. https://doi.org/10.3897/neobiota.93.121219.
Gaskin, J., West, N.M., Rector, B.G. 2024. Population structure of three invasive congeneric teasel (Dipsacus) species. Invasive Plant Science and Management. 17(1):37-45. https://doi.org/10.1017/inp.2024.5.