2012 Annual Report
1a.Objectives (from AD-416):
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.
1b.Approach (from AD-416):
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 host-specificity 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.
Progress was made on all three main objectives. For Objective 1 Biodiversity and biology of weeds, during exploration for biological control agents of Scotch thistle and Russian thistle plant specimens were collected in Turkey, Italy, and Bulgaria and were sent to cooperators for DNA analysis. For Objective 2 Host specificity and efficacy of prospective biological control agents, we measured life history responses to temperature of a psyllid, Arytainilla hakani, collected on French broom in France and conducted host specificity tests. A field experiment was conducted in Turkey, to evaluate the host plant specificity of an agent of yellow starthistle, Larinus filiformis, and of Scotch thistle, Larinus latus. Exploration for prospective agents of Scotch thistle and Salsola (common tumbleweed) were continued in Turkey, Italy, and Bulgaria. Host plant specificity evaluations were completed for two prospective agents of Cape Ivy: a stem-boring moth, Digitivalva delaireae, and the gall-forming fly, Parafreutreta regalis. Petitions for both agents were submitted to USDA-APHIS for evaluation as part of the process for requesting permission to release the agents to control Cape ivy. A prospective biological control agent of musk thistle, Urophora solstitialis, was received in quarantine, and we began host plant specificity testing (not a milestone, but was requested by a stakeholder, California Department of Food and Agriculture). Analysis of volatile organic chemicals emitted by host plants was conducted to help understand how a host-specific insect, Ceratapion basicorne, chooses its host plant. For Objective 3 Impact, work on measurement of infestation of flower heads of bull thistle by the previously released fly, Urophora stylata, was postponed for lack of staff. Populations of yellow starthistle and biological control agents were monitored at long-term study sites in California.
Biological control agent study. Yellow starthistle is an invasive alien weed that has invaded about 20 million acres of rangeland in the western USA and costs about $1.5 billion in California alone. A prospective weevil biological control agent of yellow starthistle, Ceratapion basicorne, appears to be very host specific, but it can sometimes develop on safflower in laboratory experiments. An ARS researcher at Albany, California, conducted a field experiment with foreign cooperators in Italy to evaluate the potential risk of this insect to safflower when grown as a crop. No attack of the weevil was observed in over 1,000 safflower plants that were dissected. The results indicate no significant risk that this insect will harm safflower, which should help to convince regulatory agencies that the insect is safe enough to use to control yellow starthistle. This experiment should also help clarify the differences in host specificity behavior of insects under laboratory versus field conditions, which is important for determining the safety of prospective biological control agents.
Stoeva, A., Harizanova, V., De Lillo, E., Massimo, C., Smith, L. 2011. Laboratory and field experimental evaluation of host plant specificity of Aceria solstitialis, a prospective biological control agent of yellow starthistle. Experimental and Applied Acarology. 56(1):43-55 DOI: 10.1007/s10493-011-9497-6.
Smith, L. 2012. Host plant oviposition preference of Ceratapion basicorne (Coleoptera:Apionidae), a potential biological control agent of yellow starthistle. Biocontrol Science and Technology. 22(4):407-418.