Location: Invasive Species and Pollinator Health2016 Annual Report
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.
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.
It is necessary to prioritize potential weed targets for biological control based on damage caused and inadequacy of other control methods. Under Objective 1, a list of sites was developed for surveys of two soft scale insects that feed on invasive ice plant, and their previously-introduced parasitic wasps. Scouting trips and dialogue with natural resource agencies determined which sites met all criteria for sampling. A total of 15 non-ornamental ice plant populations in dune habitats on the California coast and three along canals in the Central Valley were selected for sampling, and permits/permissions obtained. The feasibility of developing biocontrol for several potential weed targets (ice plant, yellow sorrel, woolly mullein, and jubatagrass) suggested by stakeholders was investigated through literature surveys to determine the number of close native relative plants, and discussions with stakeholders about invasive damage/benefits attributed to these weeds. A key stakeholder, the California Invasive Plant Council, completed a ranking process that took into account invasiveness, damage caused, and difficulty to control via other methods. A total of 64 weeds were ranked for suitability for biocontrol. ARS researchers in Albany, California are already working on developing new and evaluating existing agents for 10 of these; new agents are under development by other research groups for at least 10 others. Assessments of biocontrol feasibility from the point of view of biosafety (low number of close native relatives; further discussions with stakeholders) are ongoing. Also under Objective 1, the host specificity (safety), life cycles, and efficacy of new candidate biological control agents were examined. Exploration was conducted in southern France on Russian thistle to find the candidate moth Gymnancyla canella for possible future use as a biocontrol agent of Russian thistle, one of the most damaging invasive weeds in rangelands in the western U.S. Small amounts of moth larval damage was observed on previous year plants, but no pupae were collected. Target and nontarget plants are being grown at the ARS-European Biological Control Laboratory in France. The candidate French broom weevil Lepidapion argentatum was received from France for overwintering in the quarantine lab. ARS scientists in Albany used caged French broom shoot tips and male-female weevil pairs to determine the minimum day length required for successful galling on shoot tips (12 hours). A reproductive colony was established on galled shoot tips and completed four generations. Studies on the efficacy of the candidate French broom psyllid Arytinnis hakani were completed, demonstrating that the growth and survival of both small and large potted plants is reduced after one generation, and that a psyllid density of at least five per leaf is needed to kill plants. However, 2016 no-choice development tests indicated that this psyllid can develop on at least four species of lupines, French broom’s closest relatives native to the U.S. For biological control of Cape-ivy, the closely-related nontarget plants Senecio aronicoides and Senecio triangularis were obtained at field sites to verify the ability of the candidate moth Digitavalva delaireae to complete development only on Cape-ivy. Tests with Senecio triangularis found no larval feeding on leaves, corroborating prior results on other Senecio species. New biological control agents must be released, and the efficacy of previously-released agents verified and combined with other control methods, to maximize the effectiveness of biological and integrated invasive weed management. Under Objective 2, in a field plot and in greenhouse no-choice or choice tests, two previously-released yellow starthistle agents (the flower-galling fly Urophora sinuraseva and the seedhead-feeding fly Chaetorellia succinea) were more successful (i.e., produced more larvae) on a starthistle accession from San Diego than on other California accessions, and also in comparison to an accession from northern Greece, where the agents were originally collected. Another, more widespread agent, the flower head-feeding weevil Eustenopus villosus, showed no preference. Expanded field tests in 2016 with potted plants are comparing 11 accessions from California as well as Oregon to the Greek accession, and also to four accessions from France and Spain, the region where starthistle is native and is genetically closest to the invasive populations in California and Oregon. Field surveys at a state-owned recreational area in southern California invaded by Dalmatian toadflax indicated that the weevil Mecinus janthiniformis, released by ARS in 2014 after a fire destroyed the previous biocontrol population, successfully colonized Dalmatian toadflax that summer, although less than 5% of the stems in the release plots were attacked. Dissection of dead stems from 2015 indicated higher attack than in 2014, and in May 2016, adult beetles were observed dispersing from the release plots to other plants. Evidence of feeding by the larvae of a native root moth larvae was present in 3 to 8% of the roots from this site in 2015, consistent with prior years. Over 15 native plant species co-occur with the weed at the southern California site and stand to benefit from biocontrol. Two sites in far northern California (one each in Lassen and Trinity Counties) were selected for additional studies of weevil-moth associations. Also in northern California, the Scotch broom mite (Aceria genistae), which arrived on its own by dispersing from other states, was found galling shoot tips of invasive Scotch broom and was present at many sites. Field plantings are being used to determine whether it can feed on lupines, Scotch broom’s closest native relatives. The arundo wasp and arundo armored scale were released at four new sites in the Sacramento-San Joaquin Delta (total of nine sites now in this region), for biological control of the giant invasive grass known as arundo or giant reed. New sites were also identified in the Sacramento and San Joaquin River Valleys. In 2015 tests with a collaborator from Chico State University involving arundo shoots with galls or ‘tumors’ made by the arundo wasp, provided by ARS and placed in the field, no parasitism/attack on the galls was observed at three sites in the northern Sacramento Valley. For biological control of Cape-ivy, a field release permit for the Cape-ivy fly Parafreutreta regalis was received from APHIS in May 2016. The fly was reared for the first time outside of quarantine for one generation. Initial releases were completed at one field site in the Bay Area of California.
1. Field host range of non-native insect that feeds on invasive Scotch broom determined. Scotch broom has invaded about 1 million acres of rangelands and forests in California and elsewhere in the western U.S., making fields unpalatable to livestock, increasing fire risk, and displacing native plants. A non-native insect that feeds on plant sap, known as the Scotch broom psyllid, arrived on its own in California and can do significant damage to Scotch broom. A major concern was that this psyllid would damage nontarget plants, especially lupines, which are the closest native relatives to this invasive alien species. In laboratory experiments conducted by ARS scientists in Albany, California, the psyllid was able to feed and develop on one lupine species. However, in a field experiment no eggs or immature psyllids were found on lupines planted close to heavily infested Scotch brooms. These results indicate that the psyllid poses no danger to native lupines, and the insect could thus, with appropriate permits, be redistributed by resource agencies interested in improving control of Scotch broom.
2. Impact of potential biological control agent of French broom clarified. French broom has invaded 100,000 acres of coastal mountain and Sierra foothill forests and rangelands in California, increasing fire risk and displacing native plants. The French broom psyllid, native to Europe, has been released in Australia and can kill French broom plants. Conflicting information existed in the literature about the impact of the psyllid, in part because impact was measured over only one generation. In a quarantine laboratory test, ARS scientists in Albany, California, demonstrated that only 11% of the plants died after one psyllid generation, but 82% died after three generations, and the few psyllid-infested plants that survived were 66% smaller than uninfested plants. In additional tests, growth of both small and large psyllid-infested plants was reduced after one generation, and a psyllid density of six psyllids per leaf consistently killed plants. The results suggest strategies for when and how to release the psyllids to maximize biocontrol impact, in regions where it can be demonstrated that the psyllid is sufficiently host-specific for release.
Goolsby, J., Moran, P.J., Racelis, A.E., Summy, K.R., Martinez-Jimenez, M., Lacewell, R.D., Perez De Leon, A.A., Kirk, A.A. 2015. Impact of the biological control agent, Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas. Biocontrol Science and Technology. 26(1):47-60.
Hogg, B.N., Smith, L., Moran, P.J., Daane, K.M. 2016. Post-establishment assessment of host plant specificity of Arytainilla spartiophila (Hemiptera: Psyllidae), an adventive biological control agent of Scotch broom, Cytisus scoparius. Biocontrol Science and Technology. 26(7):995-1008. doi: 10.1080/09583157.2016.1178707.
Hogg, B.N., Moran, P.J., Smith, L. 2016. Multi-generational impacts of the psyllid Arytinnis hakani (Hemiptera: Psyllidae) on growth and survival of the invasive weed Genista monspessulana. Biological Control. 100(1):87-93. doi: 10.1016/j.biocontrol.2016.05.015.
Hogg, B.N., Smith, L., Daane, K.M. 2016. Impacts of the adventive psyllid Arytainilla spartiophila on growth of the invasive weed Cytisus scoparius under controlled and field conditions in California. Environmental Entomology. 45:109-116.
Madeira, P.T., Facey, J., Pratt, P.D., Maul, D., Wheeler, G.S. 2016. Are three colonies of Neostromboceros albicomus, a candidate biological control agent for Lygodium microphyllum, the same host biotype? Biocontrol Science and Technology. 26(3):440-445.
Moran, P.J., Pitcairn, M.J., Villegas, B. 2016. First establishment of the planthopper Megamelus scutellaris Berg 1883 (Hemiptera: Delphacidae) released for biological control of water hyacinth in California. Pan Pacific Entomology. 92(1):32-43. doi: 10.3956/2016-92.1.32.
Pratt, P.D., Herdonica, K., Valentine, V., Makinson, J., Purcell, M., Mattison, E.D., Rayamajhi, M.B., Raghu, S., Moran, P.J. 2016. Development rate, consumption and host specificity of Carea varipes (Lepidoptera: Nolidae). Annals of the Entomological Society of America. 109(4):513-517. doi: 10.1093/aesa/saw021.
Tipping, P.W., Martin, M., Pratt, P.D., Rayamajhi, M.B., Getty, L. 2015. Resource regulation of an invasive tree by a classical biological control agent. Biological Control. 85:12-17.