Location: Invasive Species and Pollinator Health
2020 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 hostspecific 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
This is a new bridging project that continues research from project 2030-22000-027-00D, "Management of Invasive Weeds in Rangeland, Forest and Riparian Ecosystems in the Far Western U.S. Using Biological Control," which expired in May 2020. Please see the 2030-22000-027-00D report for additional information. Initiation of a biological control (biocontrol) program requires long-term investment and significant up-front costs. It is necessary to first prioritize which weeds to target with biological control, discover candidate biocontrol agents, and begin risk assessment testing. These research activities were addressed under Objective 1.
Crystalline ice plant smothers native plants and alters soils. Under Sub-objective 1.1, collections of crystalline ice plant by overseas collaborators in South Africa and Italy began at four sites to determine this weed’s genetic origins in the United States, and to explore biocontrol agents in South Africa and the Mediterranean Basin.
The host range, biology, and effectiveness of candidate biological control agents need to be evaluated for ongoing programs. Yellow starthistle, Russian thistle, French broom, and Cape-ivy displace native plants and forage grasses in rangelands, forests, and along streams, consume scarce water, and fuel wildfires. Under Sub-objective 1.2, maximized telework prevented continuation of tests on the host range of the seedhead-feeding weevil, Larinus filiformis, on yellow starthistle, the stem-boring moth, Gymnacyla canella, on Russian thistle, and the shoot tip-galling and seed pod-feeding weevil, Lepidapion argentatum, at the ARS in Albany, California. The global Covid-19 pandemic prevented a field test on the host range of L. filiformis in Bulgaria. An addendum to a prior field release application was prepared for submission to USDA that incorporates new host range testing results for the leaf-mining and stem-boring moth, Digitivalva delaireae, a candidate biocontrol agent of Cape-ivy.
Research on the release of new weed biocontrol agents, and on evaluation of their establishment, efficacy, and integration into weed management, was completed under Objective 2. Under Sub-objective 2.1, maximized telework delayed and prevented tests of diet components to develop a mass-rearing protocol for the root- and rosette-feeding weevil, Ceratapion basicorne, a newly-permitted agent against yellow starthistle. Initial population development of the weevil at one field site, at which the weevil was released under the expired project, was monitored. Also Under Sub-objective 2.1, past field garden and greenhouse no-choice and choice test results on the reproductive performance of the seed-galling fly, Urophora sinuraseva, the seed-feeding fly, Chaetorellia succinea, and the flower- and seed-feeding weevil, Eustenopus villosus, on accessions of yellow starthistle from California, France/Spain, and northern Greece were analyzed in preparation for publication.
Dalmatian toadflax is one the most widespread invasive weeds in rangelands in the western United States, but it has been brought under control in many areas by the stem-boring weevil, Mecinus janthiniformis. Under Sub-objective 2.2, results obtained under the expired project from releases of M. janthiniformis on Dalmatian toadflax at a location in southern California, demonstrating successful weevil establishment and reduction of Dalmatian toadflax density by two-fold, were analyzed and prepared for publication.
Arundo is a giant grass that invades riparian habitats in northern California and throughout the southwestern United States. Under Sub-objective 2.3, 2,400 females of the shoot tip-galling wasp, Tetramesa romana, a known effective biocontrol agent, were released at four sites, two each in the Sacramento and San Joaquin River watersheds of California’s Central Valley. Although the wasp is established at one other site in each region, prior releases under the expired project had not led to establishment at these specific four sites. Wasps were also released at one new site in the southern Sacramento-San Joaquin Delta. Additional wasps from Texas and a separate population from southern California were released to compare their reproduction under Central Valley conditions. A greenhouse host range test of another biocontrol agent, the arundo armored scale Rhizaspidiotus donacis, was conducted to verify prior greenhouse and field results that the scale, cannot complete its full development and reproduce on a close relative, common reed.
Also under Sub-Objective 2.3, the shoot tip-galling fly, Parafreutreta regalis, was released for biological control of Cape-ivy at five sites, from Humboldt County south to Monterey County along the California coast. This fly is established at four other sites along the coast, and technology to release flies in ways to maximize establishment was applied to these five new sites, including the use of multiple caged releases, and short-term planting of greenhouse-galled plants in the field. Drought is a significant limiting factor on Cape-ivy growth in the summer in California’s Mediterranean climate. A greenhouse test was performed in which 20 plants each were exposed to 75% reduced watering in ether the adult egg-laying stage, gall and larval development stage, both, or neither (normal watering). Drought stress during larval development reduced plant size and growth, and reduced fly reproduction by over 50%. Cape-ivy flies should thus not be released on drought-stressed plants.
Accomplishments
