Biological control implementation for giant reed (Arundo donax) and Cape-ivy (Delairea odorata) in southern California

Award Period
to
Award Amount
$162,000
Agency Name
USDA Forest Service
Award Number
18-DG-11052021-227
PI First Name
Thomas
PI Last Name
 Dudley
CO-PI
Adam Lambert
Area/s of Research
Ecology and Evolution
Abstract

The bicontrol programs for the riparian weed species giant reed/arundo and Cape-ivy are at a critical stage of refinement and implementation in California. The Cape-ivy fly has developed in cages northern CA, but timing of release and warm, dry conditions likely impeded survival at the one test site in southern CA (Portman and Moran 2017). The imported arundo wasp has not yet established in northern CA (Bitume and Moran 2017) but an unintentionally introduced form of this wasp is present in southern counties (Dudley et al. 2008) and may be better suited for re-distribution in the State. The arundo armored scale was successfully transferred to plants in the field in northern CA, but the release techniques have not been tested in central and southern CA; a similar scale of uncertain identity was recently discovered in southern CA which also may offer potential for statewide re-distribution, if found to be taxonomically and ecologically similar to the imported insect.. In addition, a non-native arundo fly is sparsely present at some southern CA sites and causes significant impact; a form of this Arundo fly is the subject of pre-release overseas testing but has not yet been imported into North America.

Thus, both biocontrol programs need refining to ensure implementation success in infested coastal and inland watersheds from the Oregon border to San Diego, including taking advantage of the potential for augmentation biocontrol using specialist herbivores present in currently limited ranges. Prior experience with weed biocontrol agents shows that latitude, climate and moisture gradients influence establishment (e.g. Byrne et al. 2002, Bean et al. 2007; Reeves 2017), particularly if only one/two genotype/accessions of the agent are available, as is the case for arundo and Cape-ivy. The goal of this project is refine release methods and assess establishment and early impact of these agents in central-southern CA, in coordination with USDA cooperators in northern CA, and to evaluate the potential for re-distribution to regions where weed control is desired. The objectives are:

1. Conduct studies of specialist herbivores currently present, to determine taxonomic affinities, relationships with host plants and suitability for re-distribution to other parts of the State;

2. Release biocontrol agents into controlled field environments to assess establishment and developmental responses, , while measuring efficacy in relation to geographic and climatic factors;

3. Conduct open releases where appropriate to assess initial establishment and dispersa behaviorl;

4. Develop field monitoring protocol for subsequent (including post-project) evaluation of  impact to target weeds , and changes in plant community composition.