Location: Invasive Species and Pollinator Health2015 Annual Report
1) Characterize the diversity and basic biology of target weeds, including yellow starthistle and other weeds such as Russian thistle and Cape-ivy, estimate their potential range and environmental/economic impacts, and determine their regions of origin. 2) Discover and evaluate the host-specificity and potential efficacy of arthropod biological control agents for target weeds such as Cape-ivy, yellow starthistle, Russian thistle, French broom, and Scotch and bull thistles. 3) Evaluate the population dynamics and efficacy of biological control agents, their impact on non-target species, and relevant interactions in associated biological communities and farming systems, for weeds such as Cape-ivy, French broom, yellow starthistle, and Russian, Scotch and bull thistles.
We will develop classical biological control programs to help control invasive alien plants such as Cape-ivy, yellow starthistle, Russian thistle, French broom, and Scotch thistle. Molecular genetic methods will be used to help characterize genetic diversity of the target weeds and determine their geographic origin, which are necessary to direct foreign exploration for prospective agents. Climatological analysis of the known geographic distribution of target weeds will predict potential geographic range for invasion in the USA. Field and laboratory experiments will be used to measure the environmental and economic impacts of these target weeds. With the assistance of foreign cooperators, we will discover prospective arthropod biological control agents for the above weed targets. We will evaluate the hostspecificity and potential efficacy of these agents in experiments conducted in our quarantine laboratory and in the field where these agents are native. Host specificity bioassays and GC-MS analysis of volatile organic chemicals of target and nontarget plants will help determine the importance of plant secondary chemistry in determining specificity of prospective biological control agents. We will conduct field experiments to study the population dynamics and efficacy of biological control agents after they have been released for weeds such as Cape-ivy, French broom, yellow starthistle, and Russian, Scotch and bull thistles. This will include studies on impact on non-target species, and on possible interactions within targeted biological communities and farming systems.
This is a new replacement project that continues research from project 2030-22000-025-00D, "Biological Control of Invasive Terrestrial and Riparian Weeds in the Far Western U.S. Region, with Emphasis on Thistles, Brooms and Cape-ivy," which expired in June 2015. Please see the final Year 5 report for that project for additional information. Identifying the origins and invasive impacts of exotic weeds can provide insights to their biology and management, and detailed knowledge of the host ranges of new candidate biological control agents is essential prior to release. Under Objective 1, literature reviews and meetings with natural resource managers revealed that invasive ice plant (Carpobrotus edulis) and jubatagrass/pampasgrass (Cortedaria selloana) are high-priority targets for improved management in the far western U.S., justifying further investigation of their suitability for biological control. Yellow starthistle (Centaurea solstitialis) samples from 10 California sites were compared using microsatellite DNA analysis to samples from one site in northern Greece, in the area where several biological control agents released in the U.S. in the 1980s and 1990s were originally collected. The results agreed in part with earlier findings that that invasive yellow starthistle in California is genetically distinct from yellow starthistle in the native Greek range, suggesting that the biocontrol insects from Greece may not be fully compatible for maximum reproduction and impact on the invasive yellow starthistle in California. The results also revealed significant genetic variation among 10 California yellow starthistle populations sampled. Based on these findings, work on the new project will focus on collection of new populations of existing agents and new agents from the area where the invasive yellow starthistle in the western U.S. originated-western Mediterranean Europe. In no-choice host range tests of the Cape-ivy moth (Digitivalva delaireae) on two close native relatives (Senecio blochmaniae and Senecio flaccidus) which, based on the literature, are chemically similar to Cape-ivy (Delairea odorata), no larval damage or development occurred in four tests per species, while Cape-ivy plants exposed to adult moths produced 25-50 pupae per plant. These results suggest that the Cape-ivy moth will not cause harm to these native relatives of Cape-ivy in the field. Studies on growth of French broom (Genista monspessulana) plants grown from seed collected from invasive (California) compared to native (France and Spain) locations were conducted to determine factors that might limit efficacy of candidate biocontrol agents. Biocontrol was simulated by releasing larvae of a native moth on outdoor plants at the research facility to determine if invasive and native plants differ in tolerance and regrowth in response to herbivory. Native and invasive plants were consumed equally by this moth. The biology, efficacy and ecology of insects released as biological control agents of weeds must be thoroughly investigated. Under Objective 2, three previously-released biocontrol agents on yellow starthistle, the seedhead weevil Eustenopus villosus, the seedhead-galling fly Urophora sinuraseva, and the seedhead-feeding fly Chaetorellia succinea were assessed for differences in feeding damage and reproduction on plants grown from seed collected in California, in comparison to plants grown from seed collected from northern Greece. Potted Greek and California plants were exposed to natural populations of these insects at a field site, and both no-choice tests, involving only one California or Greek plant, and dual-choice tests with two plants from each region, were run in cages in the greenhouse. The seedheads are being dissected to determine results. The arundo wasp (Tetramesa romana) and arundo armored scale (Rhizaspidiotus donacis) were released at four new sites in the Sacramento-San Joaquin Delta and two new sites in the Sacramento River watershed for biocontrol of arundo (Arundo donax).
Reddy, A.M., Mehelis, C.N. 2015. Pre-release efficacy assessment of the leaf-mining moth Digitivalva delaireae (Lepidoptera: Glyphipterigidae), a potential biological control agent for Cape-ivy, Delairea odorata (Asteraceae), in western North America. Biological Control. 90:67-74.