Location: Invasive Species and Pollinator Health
2018 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
Initiation of a biological control program requires long-term investment with significant up-front costs. It is necessary to prioritize weed targets for biological control based on the damage they cause to natural resources, and on the feasibility and degree of efficacy of other control methods. Ice plant is a widespread invader of coastal dune, forest, and stream-side habitats in California. In Objective 1, 13 sites along the California coast were sampled for abundance of two immobile soft scale insects (Pulvinariella spp.) that were accidentally introduced decades ago, to see if they or several intentionally-introduced parasites of the scale insects are present. The soft scales were present at two sites in low density, indicative of a lack of impact. No other herbivorous insects were observed. Exit holes indicative of parasite feeding on scales were observed.
Also under Objective 1, a weed biological control prioritization process for the western U.S., developed in collaboration with scientists from Australia, neared completion. The first phase harnessed the knowledge of 187 weed scientists and land managers across 10 states to compile a list of 33 key weeds, characterize the impacts of each weed, and document management goals. The second phase used the expertise of biological control scientists and practitioners to assess the feasibility of pursuing a biological control program for each weed, and the likelihood of successfully achieving management goals. Nine weeds were identified as having low priority for biocontrol, whereas 24 were considered moderate or high priority. Six weeds were characterized as having both high prospects for successful biological control and greatest impact on natural environments. A report was drafted and the results will guide selection of targets for future weed biocontrol projects.
The biological safety (host range), life cycle and impact of new biological control agents were examined under Objective 1, as this information is essential for regulatory evaluation of applications for release. Yellow starthistle and Russian thistle are two of the most damaging weeds of rangelands in the western U.S. Sixteen adult Larinus filiformis flower-feeding weevils collected by Italian collaborators in Bulgaria were propagated on yellow starthistle, and data on fecundity, stage of flower head that they attack and survivorship were collected in the ARS European Biological Control Laboratory in France. Larvae of the stem-boring moth Gymnancyla canella collected in France on Russian thistle were reared to pupation stage. Both insects are being propagated for future shipment to the Albany, California ARS quarantine for host range studies.
French broom invades forests and rangelands in the three Pacific coast U.S. states, displacing native plants and fueling wildfires. Four greenhouse experiments were completed under Objective 1 to determine the impact of the shoot tip-galling French broom weevil Lepidapion argentatum on young French broom seedlings. In two fall and winter studies, adults damaged leaves but did not make galls. In two spring/early summer studies, adults both damaged leaves and galled shoot tips, stunting shoot growth. Galling is thus essential for impact on seedlings, and occurs only under spring/early summer daylight conditions.
Under Objective 1, ARS scientists have successfully reared the medusahead mite Aculodes altamurgiensis under laboratory conditions, and host range testing is underway. Medusahead is an annual grass that invades grazing lands and displaces forage species. Biological control may be the only sustainable method to manage this weed in the western U.S., but medusahead is a close relative to wheat and other grain crops, indicating that a high level of host specificity is required. Recent surveys of Central and Eastern Europe by an ARS collaborator in Reno, Nevada, have resulted in the discovery of this small mite in the family Eriophyidae, which includes other mite species that are highly host-specific. Collaborators in Italy shipped a colony of the mite to the ARS quarantine facility in Albany, California.
Also under Objective 1, the host range of the leaf- and stem-mining Cape-ivy moth Digitivalva delaireae, was tested on two native flowers (arrowleaf ragwort and rayless ragwort) that are related to Cape-ivy, a major invasive weed in coastal stream-side and forest habitats in California. Adults laid eggs on arrowleaf ragwort, and some eggs hatched into larvae that made small mines, but the larvae then died. In separate tests, larvae at various stages of development were transferred from Cape-ivy to arrowleaf ragwort. Large larvae killed a few leaves and pupated on arrowleaf ragwort, while small larvae made mines but then died. The results indicate that arrowleaf ragwort cannot support complete development of the moth, so it is safe to release.
Under Objective 2, new biological control agents are being released, the efficacy of released agents verified, and biocontrol combined with other control methods, to maximize effectiveness. A total of 1,630 yellow starthistle seedheads were dissected from 2017 field tests that compared four accessions of yellow starthistle from France/Spain to three from Northern Greece, for reproduction by the flower-galling fly Urophora sinuraseva, the seedhead-feeding fly Chaetorellia succinea, and the flower head-feeding weevil Eustenopus villosus. These insects were released in the U.S. over 20 years ago and were collected originally in Northern Greece. The hypothesis is that the insects would produce more offspring on Greek accessions of yellow starthistle than on accessions from France/Spain, the origin of invasive yellow starthistle in California. The seedhead fly was two-fold more abundant in the samples than the flower-galling fly, consistent with past tests. Greenhouse tests in 2017 and 2018 assessed reproduction by the flower-galling fly in cages when given a choice of one French/Spanish and one Greek accession. These results will improve understanding of the reasons why the biocontrol agents, though abundant, do not exert enough impact on yellow starthistle in California.
Also under Objective 2, surveys to determine biocontrol impact of the Dalmatian toadflax weevil, Mecinus janthiniformis, at the southernmost site in North America, a state park in Southern California, continued for a seventh year. In 2018, weevils were abundant at the release sites and up to one kilometer away at survey sites where they were not released. Dalmatian toadflax stems were larger in 2018 than 2017, but stem abundance was reduced. Twelve other plant species were recorded at survey sites. A root-boring moth (Penstemonia sp.) that has adopted Dalmatian toadflax as a host was found on less than 10% of roots, as in past years. Larvae of the root moth were collected for genetic analysis by a collaborator at the California Department of Food and Agriculture. Preliminary results suggest that moths collected at the southern site are a known native moth, Penstemonia hennei.
In previous years, USDA scientists tracked dispersal of the Scotch broom gall mite, Aceria genistae, into California and assessed its distribution. However, it remained unclear if the gall mite damages other invasive broom species or native plants. Inspection of specimens growing near heavily-galled Scotch broom plants revealed that the mite does not induce gall formation on native or exotic relatives. Potted plants were intermingled and gall mites were inoculated into the canopies of seven test species over two years. The mite induced galls on 60% of the Scotch broom plants, but no galls formed on any other species. These data indicate that the mite is host specific to the target weed and can cause substantial damage.
Also under Objective 2, new releases of biological control agents that are unique regionally or nationally continued. The giant grass known as arundo, or giant reed, consumes scarce water, obstructs flood control channels and creates fire danger along rivers throughout the Southwestern U.S. Surveys to determine the success of 2017 releases of the shoot tip-galling arundo wasp (Tetramesa romana) and the root-feeding arundo armored scale (Rhizaspidiotus donacis) were made at nine sites extending from the Northern Sacramento River watershed to the Southern San Joaquin River watershed. Releases were integrated with mechanical topping of arundo main shoot tips to stimulate production of side shoots favored by wasps. Wasp releases were integrated with herbicide application at one site. The arundo wasp was found to be established and dispersing at two sites. The success of arundo armored scale releases was assessed late in 2018. A greenhouse study revealed that the arundo wasp produces 10-20% more offspring when caged at high humidity than at normal levels. Low humidity may have limited release success at some sites in 2017. In 2018, new field releases were conducted using bagged arundo shoots that had been topped to stimulate side shoot production. This test is comparing wasps sourced from Texas release sites to less successful wasps present in coastal Southern California.
The Cape-ivy shoot tip-galling fly, Parafreutreta regalis, was released under Objective 2 at 10 coastal sites in 2017-18 from Santa Barbara northward to Humboldt County in California. Galls appeared at nine sites and galls with exit holes indicative of new adult emergence were found at five sites. In overwintering studies, galls were found at one site near San Francisco in 2018. New releases were conducted in 2018 using greater numbers of flies. An entomologist traveled to the weed’s native range in South Africa and collected Cape-ivy plant samples for a global genetic analysis of the origin of invasive Cape-ivy in California, Hawaii, and Australia, with some samples provided by overseas collaborators. The Cape-ivy fly was also collected to increase genetic diversity in colonies.
Accomplishments
Review Publications
Goolsby, J., Vacek, A.T., Salinas, C., Racelis, A.E., Moran, P.J. 2017. Host range of the European leaf sheath mining midge, Lasioptera donacis Coutin, a biological control of giant reed, Arundo donax. Biocontrol Science and Technology. 27(6):781-795.
Mckay, F., Logarzo, G., Natale, E., Pratt, P.D., Sodergren, C.J. 2017. Feasibility assessment for the classical biological control of Tamarix in Argentina. Biocontrol. 63:169-184. https://doi.org/10.1007/s10526-017-9855-3.
Moran, P.J., Wibawa, M.I., Smith, L. 2017. Tolerance of the eriophyid mite Aceria salsola to UV-A light and implications for biological control of Russian thistle. Experimental and Applied Acarology. 73(3-4):327-338. https://doi.org/10.1007/s10493-017-0205-z.
Erickson, K., Pratt, P.D., Rayamajhi, M.B., Horvitz, C. 2017. Introduction history influences aboveground biomass allocation in Brazilian peppertree (Schinus terebinthifolius). Invasive Plant Science and Management. 10(3):247-253. https://doi.org/10.1017/inp.2017.23.
Madeline, M., Goolsby, J., Vacek, A.T., Kirk, A., Moran, P.J., Cortes, E., Cristofaro, M., Bownes, A., Mastoras, A., Kashefi, J. 2018. Densities of the Arundo Wasp, Tetramesa Romana (Hymenoptera: Eurytomidae) across its native range in Mediterranean Europe and introduced ranges in North America and Africa. Biocontrol Science and Technology. 28(8):772-785.
