Location: Invasive Species and Pollinator Health
2017 Annual Report
Objectives
1) Determine the host specificity, life cycle, and efficacy of new candidate biological control agents for invasive weeds of western rangeland, forest and riparian ecosystems, such as yellow starthistle, Russian thistle, Cape-ivy, and French broom.
Subobjective 1.1: Determine feasibility of biological control of ice plant and other invasive weeds in the far western U.S.
Subobjective 1.2: Determine host specificity, life cycle, and efficacy of new biological control agents of yellow starthistle, Russian thistle, French broom, and Cape-ivy.
2) Release and evaluate new biological control agents of invasive weeds in western rangeland, forest and riparian ecosystems, and evaluate previously released and adventive agents in the context of variation in weed genotype, climatic influences, and land management regimes, including the use of other control methods.
Subobjective 2.1: Determine effect of plant genotype on efficacy of extant biocontrol agents of yellow starthistle.
Subobjective 2.2: Determine distribution and impact of adventive or recently released insects on Dalmatian toadflax.
Subobjective 2.3: Release and evaluate new biological control agents targeting arundo and Cape-ivy.
Approach
We will determine the current status of biological control of ice plant by surveying field sites for extant herbivores, including two soft scale species that feed on the leaves, and several parasitic wasps that were introduced to control these scales, over 40 years ago when ice plant was valued as an ornamental. We will determine the feasibility of biocontrol of ice plant and other candidate invasive weeds using new agents through surveys of land managers and other stakeholders, and by scoring weeds according to invasiveness, damage caused, and the likelihood of finding host-specific and efficacious biological control agents in their native ranges. These studies will take phylogenies of the weeds and related native plants into account to determine the feasibility of avoiding nontarget plant damage. We will determine the host ranges of new candidate biological control agents of yellow starthistle, Russian thistle, and French broom through overseas collection by collaborators and no-choice and choice tests in our quarantine laboratory. These studies will also evaluate the biology and impact of candidate agents on targeted weeds. We will determine the ability of the Cape-ivy moth to reproduce and feed on closely-related nontarget plants. Information from host range testing and other studies on new candidate agents will be used to submit applications to the USDA for permits for field release. We will determine the ability of previously-released biological control agents of yellow starthistle, including a seedhead-feeding weevil and a seedhead-galling fly, to damage, survive and reproduce on invasive western U.S. genotypes of yellow starthistle in relation to genotypes from the Greek native range where the agents were originally collected, and from western Mediterranean Europe, where yellow starthistle in the western U.S. originated. These studies will be conducted under no-choice and choice conditions in the greenhouse and in field plantings. New accessions of these agents will be collected from western Mediterranean Europe and evaluated for host specificity among close relatives prior to release. At field sites in southern and northern California, we will evaluate the ability of a leaf- and stem-feeding weevil to reduce invasive Dalmatian toadflax plant size and Dalmatian toadflax population size, and determine the degree of recolonization of invaded sites by native plants. We will release and evaluate the impact of a stem-galling wasp and a shoot- and root-feeding armored scale for biological control of the invasive giant grass known as arundo in the Sacramento-San Joaquin Delta and associated river watersheds, where arundo is impacting water resources. These studies will determine the effect of climate on wasp and scale establishment success. We will release and evaluate a shoot tip-galling fly for biological control of Cape-ivy at field sites along the California coast. Studies on arundo and Cape-ivy will include evaluations of agent dispersal within field sites, and of integrated biological-chemical control, in which herbicides will be applied and the ability of biocontrol agents to colonize and have impact on regrowth will be determined.
Progress Report
It is necessary to prioritize weed targets for biological control based on the damage they cause to natural resources such as water and soil, and on the costs, feasibility, and degree of efficacy of other control methods. Initiation of a biological control program requires a long-term investment with significant up-front costs. Under Objective 1, a total of 20 field sites invaded by ice plant were sampled for the presence of two immobile soft scale insects that were accidentally introduced decades ago, to see if they or several intentionally-introduced parasites of the scale insects are present. Damaging insects were not observed on ice plant, suggesting that new biocontrol agents would be needed to exert biocontrol impacts on this weed.
Also under Objective 1, through a collaboration with scientists in Australia, a three-phase process was developed to prioritize weeds of the western United States for biological control. This involved first consulting with state weed management coordinators and other relevant stakeholders to compile lists of weeds of importance to the western U.S. for prioritization as targets. Two workshops, involving stakeholders with relevant expertise were developed, to classify each weed in terms of impacts, management goals, and prospects for biocontrol. Finally, compilation of all information was used to make recommendations on priority weeds. In FY 2017, the first phase was completed and the second initiated. State coordinators, representing 10 states, provided ARS scientists with lists of weeds to take through the prioritization process. The number of weeds on each state list ranged from nine to 51. Nine state-specific on-line surveys were designed and circulated by state coordinators, and 187 stakeholders responded. Most of the weeds only occurred on one state list, but 23 occurred on three or more. Participants at the first workshop, held during a regional weed management conference, added 10 species. Workshop deliberations led to most (23) of the weed species retaining their survey-based impact level, while eight increased and two decreased in impact. Discussions enabled the identification of potential economic/environmental benefits should the weed be effectively managed by biological and integrated control. Additional discussions sought to anticipate potential conflicts of interest of biological control, for weeds that have a perceived or actual beneficial use. A second workshop, to be hosted by USDA-ARS, was planned with invited attendees who are experts in weed biocontrol research and practice in the western U.S., to assess the feasibility of biological control of the prioritized weeds.
Also under Objective 1, the biological safety (host range), life cycle and impact of new biological control agents were examined, as this information is essential for regulatory evaluation of applications for permits to release. No new biocontrol agents, or new collections of existing agents, were found in surveys of yellow starthistle in France and Spain. The seedhead weevil Larinus filiformis was collected in Bulgaria and is being reared at the ARS-European Biological Control Laboratory (EBCL) in France. One beetle (Psylliodes chalcomera) previously studied in Turkey was collected in Bulgaria and is reproducing on plants at the ARS-EBCL, to establish a colony for import, along with the weevil, to the ARS in Albany, California. Attempts to collect a moth (Gymnancyla canella) that feeds on Russian thistle in southern France failed last fall. Additional surveys are ongoing. Studies on the French broom psyllid Arytinnis hakani were completed, confirming that the psyllid can develop for multiple generations on several lupines, French broom’s closest relatives in the U.S., and can affect the growth and survival of at least one lupine species. These results preclude the release of the psyllid in the U.S. for biocontrol. The results of the rigorous psyllid host range and impact studies are useful for other regions where the psyllid is found on invasive French broom, such as Australia.
The shoot tip-galling French broom weevil Lepidapion argentatum was reared successfully in the ARS Albany, California quarantine, using a technique developed to facilitate emergence of adult weevils outside of shoot tip galls. The first study on the impact of this weevil on small seedlings was conducted. Galling of small seedlings may reduce spread of French broom from seed. The Cape-ivy moth Digitivalva delaireae was tested on several of Cape-ivy’s closest North American relatives including Senecio aronicoides, which has some of the same attractant chemicals as Cape-ivy. Adult moths laid eggs on both Cape-ivy and on nontarget plants, but no development to pupation occurred. Additional tests with one to two other species in the genus Senecio are ongoing, but results so far indicate that the moth is safe for release in the U.S. for biocontrol of Cape-ivy.
Under Objective 2, new biological control agents must be released, the efficacy of released agents verified, and biocontrol combined with other control methods, to maximize effectiveness. Over 1,000 seedheads of yellow starthistle were dissected from a field test in 2016 that compared 11 accessions from California and Oregon to one accession from northern Greece. The flower-galling fly Urophora sinuraseva, the seedhead-feeding fly Chaetorellia succinea, and the flower head-feeding weevil Eustenopus villosus, all released in the U.S. 20-30 years ago, were all collected originally in northern Greece, and the hypothesis was that these insects would produce more offspring on the Greek accession. Four accessions from Mediterranean France and Spain, the region where starthistle is genetically closest to the invasive populations in California and Oregon, were also included. In 2017, a third field test was conducted, focusing on four French/Spanish accessions and three northern Greek accessions, as well as greenhouse tests. In a collaboration between ARS and University of California-Berkeley, collections of both yellow starthistle and biocontrol agents were made throughout California ("Using Landscape Genetics to Explore Factors Affecting the Biological Control of Yellow Starthistle,") to compare the genetic ‘fingerprints’ of the plant and insects collected from various U.S. and European locations, in relation to the patterns of feeding damage and reproduction by biocontrol agents on yellow starthistle observed in our field tests.
Also under Objective 2, overwintering of the Dalmatian toadflax weevil (Mecinus janthiniformis) was examined for the first time at the southernmost release location in North America, located in northern Los Angeles County. At one of three release sites, the Dalmatian toadflax weevil increased five-fold in abundance in 2016 and 2017 compared to prior years, dispersed to survey points at which weevils were not released, and showed 50% or higher overwintering survival in Dalmatian toadflax stems. Overwintered weevils were re-released at two other 2014 release sites on this state-owned property to facilitate weevil dispersal. Fifteen plant species other than Dalmatian toadflax were surveyed as a measure of beneficial impact of biocontrol. A native moth (Penstemonia sp.) that feeds on the roots of Dalmatian toadflax was surveyed at this southern site, and also two sites in far northern California to which the Dalmatian toadflax weevil has dispersed on its own from other states. Fewer than 10% of the roots contained evidence of moth feeding, making it impossible to examine interactions between the weevil and moth in the field.
Scotch broom (Cytisus scoparius) is an exotic bush that displaces native and important forage species and disrupts forestry management. A gall forming mite (Aceria genistae), discovered as an accidental introduction on Scotch broom plants in 2005 near Tacoma, Washington, is known to cause significant damage to Scotch broom in its native European range, as well as in New Zealand where it was intentionally introduced as a biological control agent. ARS scientists surveyed broom-infested areas of California, resulting in the discovery of galled Scotch broom plants across nine counties. The highest concentration of galled plants occurred in a five-county area in the western foothills of the Sierra Nevada, and damage levels appeared sufficient to reduce Scotch broom growth and/or seed production. Dispersal of the gall mite into California has led to tests of the ability of the gall mite to feed on native lupines, to determine if the mite is safe for redistribution as a biocontrol agent.
Biological control agents that are regionally or nationally new were released under Objective 2. The arundo wasp (Tetramesa romana) and the arundo armored scale (Rhizaspidiotus donacis) were released at seven sites, including three in the Sacramento River watershed, three in the San Joaquin watershed, and one in the Sacramento-San Joaquin Delta. Releases compared the effect of three different mechanical control methods on agent establishment. Plots were either cut to ground level, 1 meter height, or not cut, before releasing biocontrol agents. Baseline data were collected on live and dead arundo shoot density and biomass. The Cape-ivy fly Parafreutreta regalis was released for the first time nationally at seven coastal sites near streams, where Cape-ivy is most-invasive, in five counties in Northern California in late 2016. This fly makes galls in the shoot tips of Cape-ivy. Galls were observed at four sites by April 2017. Additional releases were made in 2017 at sites extending northward to Humboldt County and southward to Santa Barbara County.
Accomplishments
1. New biological control agent released targeting Cape-ivy. Cape-ivy is one of California’s worst coastal invasive weeds, choking streams that provide water for high-value agriculture and smothering native plants. ARS scientists in Albany, California released a fly that makes tumor-like galls in shoot tips from Cape-ivy’s native range in South Africa. This is the first biocontrol agent in the world targeting Cape-ivy, which is also invasive in Hawaii, as well as in Australia and southern Europe. The fly was initially released at 10 sites from Santa Barbara to Sonoma Counties, survived the winter, and made galls by the summer of 2017. The release protocol included baseline monitoring of Cape-ivy plant vigor and biodiversity of other plants, to facilitate future monitoring of biocontrol impact. These releases have spurred interest among natural resource managers all along the California coast to learn more about the Cape-ivy biocontrol program, and several have asked ARS to conduct biocontrol releases on their sites as part of their integrated control programs against Cape-ivy.
Review Publications
Moran, P.J., Vacek, A.T., Racelis, A.E., Pratt, P.D., Goolsby, J. 2017. Impact of the arundo wasp, Tetramesa romana (Hymenoptera: Eurytomidae) on biomass of the invasive weed, Arundo donax (Poaceae: Arundinoideae) and on revegetation of riparian habitat along the Rio Grande in Texas. Biocontrol Science and Technology. 27:96-114.
Pratt, P.D., Herdocia, K., Valentin, V., Makinson, J., Purcell, M., Mattison, E.D., Rayamajhi, M.B., Moran, P.J., Raghu, S. 2016. Development rate, consumption, and host fidelity of Neostauropus alternus (Walker, 1855) Lepidoptera: Notodontidae. Pan Pacific Entomology. 92(4):200-209. doi:10.3956/2016-92.4.200.
Hogg, B.N., Moran, P.J., Smith, L. 2017. Impacts of the psyllid Arytinnis hakani on invasive French broom in relation to plant size and psyllid density. Environmental Entomology. 46(3):552-558. doi: 10.1093/ee/nvx074.
Hopper, J.V., Pratt, P.D., McCue, K.F., Pitcairn, M.J., Moran, P.J., Madsen, J.D. 2017. Spatial and temporal variation of biological control agents associated with Eichhornia crassipes in the Sacramento-San Joaquin River Delta, California. Biological Control. 111:13-22. doi:10.1016/j.biocontrol.2017.05.005.
