Skip to main content
ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #430049

Research Project: Watershed-scale Assessment of Pest Dynamics and Implications for Area-wide Management of Invasive Insects and Weeds

Location: Invasive Species and Pollinator Health

2017 Annual Report

The overall objective of this project is to conduct research to understand the biogeography of invasive pest species and the ecology of invaded systems at a large spatial scale relevant to solving critically important invasive weed and insect pest problems. Sustainable solutions to these problems have been elusive when traditionally approached at smaller, local scales. Geospatial variation in physical and biological processes across aquatic, riparian and agricultural ecosystems can drive pest abundance and affect impacts to entire watersheds, and knowledge is needed to develop effective spatially explicit management approaches and ultimately to improve environmental quality. Specifically, we will focus on the following assigned objectives. Objective: 1) Identify and quantify biological and ecological processes underlying the colonization and spread of key invasive aquatic and riparian plant species in the Sacramento-San Joaquin Delta–San Francisco Bay, and other impacted watersheds, including the effects of spatially diverse physical processes, environmental conditions, and management strategies on these weeds. Subobjective 1A: Evaluate spatially diverse processes and environmental conditions and their relationship to the colonization, spread and management of aquatic and riparian weed species. Subobjective 1B: Evaluate the role of phenotypic plasticity and genetic differentiation on the capacity of invasive aquatic plants/populations to maintain fitness in response to climate change. 2) Develop scientific monitoring methods to guide geospatially-explicit adaptive management for invasive weeds of western watersheds (e.g., water primroses, curlyleaf pondweed, water hyacinth, Brazilian waterweed, and cordgrasses), and develop integrated weed management and watershed restoration strategies effective under various climate scenarios and at landscape scales. Subobjective 2A: Develop geospatially-explicit monitoring methods to guide adaptive management of invasive weeds in Pacific western watersheds. Subobjective 2B: Determine the efficacy of aquatic weed biological control as influenced by pesticide use and evaluate non-target impacts of pesticides on aquatic food webs at watershed reaches adjacent to agricultural lands. Subobjective 2C: Determine invasive pest impacts and develop integrated ecological restoration - pest management strategies to overcome pest impacts and achieve restoration goals under climate/environmental change conditions. 3) Develop integrated pest management (IPM) programs for the control of key invasive insect and mite pests, such as brown marmorated stink bug, spotted wing drosophila, and light brown apple moth, attacking specialty crops in the Sacramento-San Joaquin.

We will evaluate the influence of hydrology, water management and other environmental factors on the spatial variation in propagule pressure, dispersal and establishment of Ludwigia hexapetala throughout the Russian River watershed using field experiments. We will evaluate mechanisms underlying distribution and spread of South American spongeplant in the Sacramento-San Joaquin Delta (Delta) and develop a GIS-based model to predict movement and new invasion sites. We will document release efforts, quantify spatial extent of establishment success and measure geographic range expansion of the saltcedar leaf beetle Diorhabda elongata 10 years following its release in Cache Creek Watershed. The effect of salinity and inundation on survival, growth and dispersal of invasive Iris pseudacorus will be assessed at watershed and landscape scales through field research and mesocosm experiments. In a cross-continent comparative experiment, phenotypic plasticity in germination responses of Ludwigia cytotypes to increasing temperature under predicted climate change conditions will be determined for risk assessments. Decision support tools integrating remote and field-based monitoring techniques for aquatic weeds in the Delta will be developed using remote sensing technology and ground-truthing studies. We will evaluate the water hyacinth planthopper and the water hyacinth weevil for integrated management of water hyacinth in the Delta in areas with and without pesticide applications for weed and mosquito control. Field research at multiple sites representing climatic variation will be conducted to assess aquatic invertebrate community responses to integrated weed management of aquatic weed mats (water hyacinth and Brazilian waterweed) and pesticide runoff in the Delta using a Before, After, Control, Intervention (BACI) experimental design. In the Russian River watershed, we will evaluate aquatic plant community distribution, composition and diversity relative to invasion and abundance of Ludwigia hexapetala, flow patterns and other environmental variables to develop future competitive interaction experiments and support reach-scale restoration strategies. To support control of insect pests on specialty crops in California, we will quantify regional dispersal patterns of the brown marmorated stink bug (BMSB) and spotted wing drosophila (SWD) as influenced by specialty crop type (grape, asparagus, cherry, almond, pear and walnut) and proximity to alternative susceptible hosts including invasive blackberry (Rubus armeniacus) in the Delta. BMSB populations are projected to reach outbreak levels in the Delta but this research will focus on SWD if densities of BMSB fail to reach sufficient levels to be studied at this scale.

Progress Report
In support of Objective 1, ARS scientists are evaluating how environmental variation in watersheds influences dispersal and colonization of water primroses. We conducted repeated sampling of buoyant, asexual fragments of Uruguayan primrose-willow at five sites in the Russian River to assess variation of dispersal with river flow in the watershed. Results suggest pulse recreational disturbance events best explain fragment dispersal patterns. Highest fragment capture rates were in the middle reaches of the watershed. Here fragments also bore 83% greater rooted stem nodes, a trait associated with greater establishment success, than fragments captured elsewhere. Results suggest a need for prioritized management of primrose-willow in the middle region of the river. We refined and implemented a field experiment to quantify the survival and growth of water primrose fragments landing in different substrate conditions, which will continue next year. Under Objective 1, we experimentally evaluated seed germination of invasive water primrose populations from two invaded ranges. Mature seed capsules were collected from invasive water primrose in the Russian and Loire River watersheds of California and northwestern France. In a growth chamber experiment, we compared the germination capacity of two species from the two ranges under three degrees Celsius warming predicted in climate change models. Under all tested temperatures, the germination rates were greater than 80% for water primrose from California. Warming treatments accelerated the time to germination of seeds from both invaded ranges, confirming germination capacity will be maintained under model-predicted temperature scenarios. We conducted a second on-going experiment in outdoor mesocosms simultaneously at Davis, California and Rennes, France using reciprocal transplants of seeds. Also in support of Objective 1, we implemented a second year of drogue tracking to identify the amount of plant movement for both water hyacinth and South American spongeplant in the Sacramento/San Joaquin Delta. Tracking studies are performed twice per month, once per month per species, throughout the year. Global positioning system (GPS)-equipped drogue studies are supplemented with GPS mapping of mat margins to measure mat growth, and remote sensing activities using the hyacinth mapper utility developed for the Delta Regional Areawide Aquatic Weed Project. Initial results indicate that plants typically move less than anticipated. Results of this effort will contribute to an overall spatial model and decision support tool being developed under the Areawide Project. Overall, this project contributed to Objectives 1 and 2 with significant progress on integrated, adaptive management of water hyacinth, Brazilian waterweed and arundo in the Sacramento-San Joaquin Delta. Ten years following the release a leaf beetle species, surveys were completed on a beetle introduced as a biological control agent of the exotic saltcedar tree, for the insect’s northern California distribution. This research revealed that beetles remain established in saltcedar-dominated watersheds, but spread of the beetle is limited to the original release area and another nearby watershed, with no dispersal into nearby areas infested with the tree. It is clear that saltcedar remains a serious problem where the beetles are established, indicating that the biological control agent has not been successful at suppressing the invasive weed. These findings indicate that environmental or behavioral factors limit the long range spread of the biological control agent in California. Invasive yellow flag iris populations are an increasing threat to ecological restoration projects in the Sacramento-San Joaquin Delta and other estuaries. To support Objective 1, ARS scientists are collaborating with California State University (2030-22000-029-09S, "Ecology and Spread of Invasive Yellow Flag Iris With Climate Change - Sea Level Rise in San Francisco Bay-Delta and Pacific Coast Estuaries") and University of Seville, Spain, to quantify ecological impacts of iris populations, and to assess their physiological tolerances and changes in growth dynamics with increases in estuarine salinity and inundation regimes. Data collection on plant community and soil characteristics phases are complete and evaluation of benthic invertebrates in invaded vs. uninvaded plots at three Delta sites are underway. Studies of iris distribution, abundance, plant traits, and environmental variables are in progress at multiple Delta sites, and in Los Penasquitos estuary, California. Seed collections will be completed this growing season to support manipulative experiments. To support Objective 2, ARS scientists collected data on the spatial distribution and abundance of submersed aquatic plants to evaluate the use of spatially-explicit tools to determine the effectiveness of plant management activities on invasive aquatic plant abundance and on the impacts on native plants. These evaluations included presence/absence point intercept sampling, biomass sampling, and hydroacoustic sampling. Subsequently, ARS scientists collected data to directly compare hydroacoustic sampling to biomass of submersed plants at treated and untreated sites. Results of these studies will assist in parameterizing monitoring techniques for operational programs in the Sacramento/San Joaquin Delta, focused on management of invasive Brazilian waterweed. Also under Objective 2, ARS scientists verified the establishment of a planthopper at one site in the San Joaquin River watershed. Releases and verification in the Sacramento-San Joaquin Delta were delayed due to a vacant position for this element, and by a requirement for toxicity testing of Federally-listed Delta smelt and Chinook salmon. A collaborator at University of California (UC) Davis (2030-22000-029-05S, "Areawide Management of Invasive Weeds in the Sacramento/San Joaquin River Delta: A Cooperative Inter-Agency Approach") exposed Delta smelt to dead planthoppers supplied by ARS. Feeding occurred but there was no acute toxicity (mortality). Rainbow trout, used as a surrogate for listed salmonid fish species, also showed no toxic response. ARS scientists documented 10-fold seasonal and spatial variation in densities of the one water hyacinth biocontrol agent in the Delta, the water hyacinth weevil, and found that the weevil was not exerting sufficient impact on water hyacinth to reduce growth. Water hyacinth invasion in the Delta is managed with herbicides applied in strips that generate large areas of mixed decaying and living vegetation. To further support Objective 2, ARS scientists used a Before, After, Control, Intervention experiment to sample invertebrates per gram water hyacinth biomass before and four weeks after glyphosate applications in treated and untreated locations to assess whether decaying hyacinth sustained invertebrate communities. Results documented more invertebrates per gram water hyacinth at all sites after treatment but no detectable differences between control and treated sites in species richness or evenness for either sample period. Dissolved oxygen levels decreased in some treated areas, but to levels highly unlikely to harm invertebrates. This study demonstrates that even decaying water hyacinth serves as habitat for invertebrates that are forage for endangered Delta fish species. Results provided valuable feedback for adaptive management of water hyacinth and present a framework for reconciling invasive species management efforts with food web functions anywhere water hyacinth occurs with food webs that support threatened and endangered fish species. To support Objective 2 and riverine restoration strategies, ARS scientists collected an additional year of data on the distribution of abundance of water primrose, and data on associated plant species, flow data and other environmental variables in the Russian River watershed. Community dynamics of initial datasets collected under multiple years of extreme drought conditions were analyzed. Further analyses of these data are underway to include data acquired under contrasting flood year conditions in 2017 to improve insights into invaded plant community dynamics and potential restoration pathways for recovery of native plant communities. To support Objective 3, ARS scientists initiated studies on dispersal of spotted wing drosophila (SWD) and its natural enemies at 10 organic cane berry (raspberry or blackberry) fields. SWD and its parasitoids are being trapped along transects extending 150 meters (m) into crop fields and 50m into adjacent non-crop habitats containing wild blackberry, a key host of SWD. Brown marmorated stink bug was a focus of the project plan, but has not reached high densities in California. Conversely, the bagrada bug (Bh) has become a major pest of cole crops. To monitor it and its resident natural enemies, Bh numbers were counted and Bh eggs were deployed at 22 patches of known weed hosts of Bh, which were adjacent to cole crops whenever possible. Sampling in crop fields will begin in mid-summer, when Bh is known to start leaving weed patches. Three species of Bh parasitoids from Pakistan were imported and established in quarantine, and are being tested for efficacy and safety.

1. Delta Region Areawide Aquatic Weed Project improves aquatic weed control. ARS scientists in Albany and Davis, California, led an interagency project funded under the USDA-ARS Areawide Pest Management Program that led to the implementation of a new adaptive management framework for aquatic weeds in the Sacramento-San Joaquin Delta of Northern California. Satellite data from the National Aeronautics and Space Administration (NASA-Ames) demonstrated a 20% decrease in peak annual acreage of water hyacinth in the Delta between 2014 and 2016, and a shift in the timing of peak coverage from October to July, significant because peak critical water pumping out of the Delta to the Central Valley occurs in the fall. The Division of Boating and Waterways-California Department of Parks and Recreation used expert knowledge provided by ARS and collaborators to improve management. Models of nutrient and pesticide runoff from the upstream Sacramento and San Joaquin River watersheds were constructed in the ARS Soil Water Assessment Tool (SWAT) framework by a University of California (UC)-Davis collaborator. NASA-Ames collaborators integrated those models into a Delta-SWAT model, and used it to predict water hyacinth growth, working with ARS and UC-Davis scientists. An economist at UC-Davis used plant growth outputs and data on the costs of aquatic weed control and the economic damage the weeds cause, to develop aquatic weed control scenarios to minimize treatment cost while protecting water resources and navigation.

Review Publications
Chen, H., Luo, Y., Potter, C., Moran, P.J., Grieneisen, M.L., Zhang, M. 2017. Modeling pesticide diuron loading from the San Joaquin watershed into the Sacramento-San Joaquin Delta using SWAT. Water Research. 121:374-385. doi: 10.1016/j.watres.2017.05.032.
Grewell, B.J., Skaer Thomason, M.J., Castillo, J.M., Drenovsky, R.E. 2016. Phenotypic plasticity and population differentiation in response to salinity in the invasive cordgrass Spartina densiflora. Biological Invasions. 18:2175-2187.
Castillo, J.M., Grewell, B.J., Pickart, A., Figuerora, M.E., Sytsma, M.D. 2016. Variation in tussock traits of the invasive cordgrass Spartina densiflora along the Pacific Coast of North America. Biological Invasions. 18:2159-2174.
Gillard, M., Grewell, B.J., Deleu, C., Thiebaut, G. 2016. Climate warming and water primroses: germination responses of populations from two invaded ranges. Aquatic Botany. 136(2017):155-163.
Hopper, J.V., Pratt, P.D., McCue, K.F., Pitcairn, M.J., Moran, P.J., Madsen, J.D. 2017. Spatial and temporal variation of biological control agents associated with Eichhornia crassipes in the Sacramento-San Joaquin River Delta, California. Biological Control. 111:13-22. doi:10.1016/j.biocontrol.2017.05.005.
Madsen, J.D., Wersal, R.M. 2017. A review of aquatic plant monitoring and assessment methods. Journal of Aquatic Plant Management. 55(1):1-12.