Location: Invasive Species and Pollinator Health
2023 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.
Subobjective 1A: Determine point(s) of origin of ice plant.
Subobjective 1B: Discover, identify, and prioritize candidate agents of cheatgrass, medusahead and ice-plant.
Subobjective 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.
Subobjective 2A: Deleted.
Subobjective 2B: Evaluate host range, biology and potential efficacy of candidate agents on yellow starthistle, Russian thistle, French broom, cheatgrass, medusahead, ice plant, and arundo.
Subobjective 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.
Subobjective 3A: Rear, release and evaluate a new biological control agent of yellow starthistle.
Subobjective 3B: Release and evaluate biological control agents on bagrada bug and spotted-wing drosophila.
Subobjective 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
Samples from southwestern South Africa are closest to those from California, and these areas are climatically similar. A total of 91 leaf and 279 seedhead samples of invasive stinkwort were shipped from California to the ARS European Biological Control Laboratory (EBCL) in France for genetic analysis.
Cheatgrass and medusahead are invasive annual grasses covering millions of acres in western U.S rangelands, consuming water, degrading forage quality and fueling wildfires. In support of Sub-objective 1B, an ARS scientist in Albany, California, conducted the second year of a large-scale sampling, targeting cheatgrass and a native grass to gain insights into: 1) how cheatgrass modifies the rhizosphere (soil-root interface) microbiome to facilitate its success; 2) the nature of competitive interactions that may limit establishment of microbial biological control agents; and, 3) whether local isolates (strains) of a bacterium, Pseudomonas fluorescens, are more effective in controlling cheatgrass than previously-studied strains. DNA analyses from soil samples are ongoing to identify microbial community differences across sites and between plant species.
Also in support of Sub-objective 1B, a cooperator in South Africa studied the host range of a stem-boring weevil, Lixus carinerostris, as a candidate biological control agent of crystalline ice plant. It was not able to develop on South African members of the only two genera of the same plant family (Aizoaceae) that have native members in North America. An ARS scientist from Albany, California, visited 10 sites in South Africa, collecting samples and making ecological observations. A cooperator in Italy visited the Canary Islands (Spain), Morocco and Egypt and collected a root-feeding weevil on slenderleaf ice plant. In collaboration with ARS scientists in Sidney, Montana, and Fort Detrick, Maryland, two ARS scientists in Albany, California, conducted studies on germination and reproduction of common crupina, an invasive weed of rangelands in the Pacific U.S. states to support efforts to release a new fungal biological control agent.
Since 2008, 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, wasps were collected from known host plants of bagrada by a cooperator at three sites in South Africa. Samples are being sorted for potential parasitic wasps that attack bagrada bug. Four infested sites were located on the island of Cyprus for collection of parasitic wasps.
Candidate agents of weeds and pest insects must be rigorously evaluated in a quarantine laboratory and, when possible, in the native range, to determine their host range (safety), biological life cycles and impact. These studies were completed under Objective 2.
Yellow starthistle (YST) consumes water, displaces native plants, and hinders cattle and horse grazing. In support of Sub-objective 2B, an ARS scientist in Albany, California, imported 40 adults of the seedhead weevil (beetle) Larinus filiformis from Bulgaria to evaluate its ability to complete development on four rare native U.S. relatives of YST in quarantine. Weevils laid no eggs on any of the U.S. plants.
Russian thistle displaces native plants in rangelands, consumes scarce water resources and fuels wildfires. In support of Sub-objective 2B, over 200 pupae of Gymnancyla canella, a stem-boring and fruit-eating moth, were collected by collaborators at the ARS EBCL in France and imported by an ARS scientist in Albany, California, where they are expected to emerge in late summer 2023 for host-range and biological studies.
French broom is a woody shrub that invades pastures and displaces native flora in coastal and forest ecosystems. In support of Sub-objective 2B, an ARS scientist in Albany, California, continued studies on the shoot tip-galling weevil Lepidapion argentatum, testing its ability to complete development on four native lupine species. The weevil developed only on French broom.
Under Sub-objective 2B, native microbes were evaluated by an ARS scientist in Albany, California, as biological control agents targeting medusahead and cheatgrass. DNA was extracted from seven previously-identified strains of the bacterium P. fluorescens and submitted for sequencing, as prior research indicated that this species holds potential for biological control of medusahead. Culturing of this and related species from soils collected from the biogeographical survey from 1B has been initiated. An ARS scientist in Albany, California, and international collaborators, discovered unidentified rust-like fungal pathogens on cheatgrass in Greece and Armenia. A shoot base-galling weevil was collected for the first time on cheatgrass in Greece and differentiated from known cereal pests using DNA fingerprinting. Gall midges (Stenodiplosis tectori) were collected from cheatgrass in Greece to support host-range and other testing in laboratories of international collaborators. Host-range and impact studies of Aculodes altamurgiensis and A. marcelli, two mites discovered on medusahead and cheatgrass, respectively, were initiated by international collaborators.
Arundo consumes water and fuels wildfires in the southwestern United States. Under Sub-objective 2B, the leafminer Lasioptera donacis was collected in Italy by an ARS scientist in Albany, California, and reared in the quarantine laboratory. Experiments to expose this fly to California fungal material isolated from arundo leaf sheaths were not successful but are continuing.
In support of Sub-objective 2C, an ARS scientist continued testing the host specificity of the exotic bagrada bug egg parasitoid Gryon aetherium. Choice tests (20) were conducted with the native stinkbug Holcostethus abbreviatus, which occurs on the same host plants as bagrada bug and was attacked by G. aetherium at higher rates than any other non-target species in no-choice tests. The wasp clearly 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 and release of the rosette weevil Ceratapion basicorne targeting yellow starthistle (YST) continued. An ARS scientist recorded YST density, root damage, and plant diversity at three California release sites. A planned fourth release of C. basicorne was postponed due to microbial contamination of the weevil colony. A protocol to detect insect DNA in damaged YST roots is being developed, as rosette weevils have not yet been collected from damaged roots at the California release sites. Efforts to rear C. basicorne on artificial diets continued, but 0 of 134 weevil larvae placed on experimental diets completed development.
In support of Sub-objective 3B, an ARS scientist in Albany, California, conducted surveys of the distribution and impact of the recently-discovered exotic wasp G. aetherium and other parasites attacking bagrada bug eggs at four California sites. Parasitism was monitored in eggs collected from soil. G. aetherium was present at all sites. Of the 31,759 bagrada bug eggs collected, 8.36 percent (%) were parasitized by G. aetherium and only 0.01% by other wasps. Discovery efficiency (the ability of parasitoids to locate egg patches) was 80% or higher at three of the sites, but exploitation efficiency (the ability of parasitoids to exploit each egg patch) was less than 20%, suggesting that G. aetherium can locate egg patches efficiently but is less efficient at attacking all eggs.
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, with up to $1B in projected losses nationwide. In support of Sub-objective 3B, 1,400 adult wasps of Ganaspis brasiliensis, a new non-native 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. No G. brasiliensis were recovered, although two naturally occurring wasp species were collected. However, G. brasiliensis offspring were recovered from field cages infested with both SWD and the parasite, suggesting that conditions were suitable for G. brasiliensis.
Cape-ivy invades forests and scrublands along the California coast. In support of Sub-objective 3C, measurements of impact continued at three sites at which the shoot tip-galling fly Parafreutreta regalis is established, and establishment verified at seven more sites. A study on integrated management was carried out on potted plants to determine if the fly could limit regrowth after simulated herbicide treatment. However, flooding destroyed this site. Studies were initiated at a site in a California State Park.
Accomplishments
Review Publications
Hougardy, E.H., Hogg, B.N., Wang, X., Daane, K.M. 2022. Discrimination abilities and parasitism success of pupal parasitoids towards spotted-wing drosophila pupae previously parasitized by the larval parasitoid Ganaspis brasiliensis (Hymenoptera: Figitidae). Environmental Entomology. 51(6):1106-1112. https://doi.org/10.1093/ee/nvac083.
Hogg, B.N., Nelson, E.H., Daane, K.M. 2023. A comparison of candidate banker plants for management of pests in lettuce. Environmental Entomology. 52(3):379-390. https://doi.org/10.1093/ee/nvad029.
Hougardy, E.H., Hogg, B.N. 2022. Factors affecting progeny production and sex ratio of Gryon aetherium (Hymenoptera: Scelionidae), a candidate biological control agent for Bagrada hilaris (Hemiptera: Pentatomidae). Insects. 13(11). Article 1010. https://doi.org/10.3390/insects13111010.
Goolsby, J., Moran, P.J., Martinez Jimenez, M., Yang, C., Canavan, K., Paynter, Q., Ota, N., Kriticos, D. 2023. Biology of invasive plants 4. Arundo donax L. Invasive Plant Science and Management. 16(2):81-109. https://doi.org/10.1017/inp.2023.17.
Young, S.L., Archer, D.W., Blumenthal, D.M., Boyd, C.S., Clark, P., Clements, D.D., Davies, K.W., Derner, J.D., Gaskin, J.F., Hamerlynck, E.P., Hardegree, S.P., Jensen, K.B., Monaco, T.A., Newingham, B.A., Pierson Jr, F.B., Rector, B.G., Sheley, R.L., Toledo, D.N., Vermeire, L.T., Wonkka, C.L. 2023. Invasive annual grasses: re-envisioning approaches in a changing climate. Journal of Soil and Water Conservation. 78(2):95-103. https://doi.org/10.2489/jswc.2023.00074.
Cabrera Walsh, G., Sosa, A.J., Mc Kay, F., Maestro, M., Hill, M., Hinz, H., Paynter, Q., Pratt, P.D., Raghu, S., Shaw, R., Tipping, P.W., Winston, R.L. 2023. Is biological control of weeds conservation’s blind spot? Quarterly Review of Biology. 98(1):1-28.
Vidovic, B., Andelkovic, N., Jojic, V., Cvrkovic, T., Petanovic, R., Marini, F., Cristofaro, M., Rector, B.G. 2022. A new Aculodes species (Prostigmata: Eriophyidae) described from an invasive weed by morphological, morphometric and DNA barcode analyses. Insects. 13(10). Article 877. https://doi.org/10.3390/insects13100877.
Young, S.L., Anderson, J.V., Baerson, S.R., Bajsa Hirschel, J.N., Blumenthal, D.M., Boyd, C.S., Boyette, C.D., Brennan, E.B., Cantrell, C.L., Chao, W.S., Chee Sanford, J.C., Clements, D.D., Dray Jr, F.A., Duke, S.O., Porter, K.M., Fletcher, R.S., Fulcher, M.R., Gaskin, J., Grewell, B.J., Hamerlynck, E.P., Hoagland, R.E., Horvath, D.P., Law, E.P., Madsen, J., Martin, D.E., Mattox, C.M., Mirsky, S.B., Molin, W.T., Moran, P.J., Mueller, R.C., Nandula, V.K., Newingham, B.A., Pan, Z., Porensky, L.M., Pratt, P.D., Price, A.J., Rector, B.G., Reddy, K.N., Sheley, R.L., Smith, L., Smith, M., Snyder, K.A., Tancos, M.A., West, N.M., Wheeler, G.S., Williams, M., Wolf, J.E., Wonkka, C.L., Wright, A.A., Xi, J., Ziska, L.H. 2023. Agricultural Research Service weed science research: past, present, and future. Weed Science. 71(4):312-327. https://doi.org/10.1017/wsc.2023.31.
