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

2016 Annual Report

Objectives
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.

Approach
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
This report documents substantial progress made on all three objectives of Project Number 2030-22000-029-00D, "Watershed-scale Assessment of Pest Dynamics and Implications for Area-wide Management of Invasive Insects and Weeds" which started December 2015, and expands the scope of research from the previous project, 2030-22000-024-00D, "Landscape-Level Assessment and Management of Invasive Weeds and their Impacts in Agricultural and Natural Systems." Aquatic Ludwigia species (water primroses) have aggressively invaded watersheds in the Pacific west and Florida. In support of Objective 1, ARS scientists at Davis, California, are evaluating how spatial and temporal variability of environmental conditions within watersheds influence the propagule pressure, dispersal, colonization and spread of Ludwigia spp. Study sites were established in the Russian River watershed. Methods were developed, tested and refined to evaluate impact of asexual ramet length and release site on ramet dispersal distance, survival and resprouting capacity. A pilot scale field experiment was deployed for a multi-year assessment of factors supporting fragment colonization and demographic success that may be influenced by water management. Also under Objective 1, study populations were identified, and mature seed capsules were collected from Ludwigia taxa of differing ploidy levels in the invaded Russian River and Loire River watersheds of California and Brittany, France. A permit was obtained from California Department of Food and Agriculture for importation of seeds from France. Pilot experiments were initiated to evaluate seed viability and comparative germination responses to increasing temperature under predicted climate change conditions. Experiments are underway in climate controlled growth chambers, and also in contrasting outdoor conditions in California and Brittany. Substantial progress has been made towards the 2016 evaluation of aquatic plant community distribution, composition and diversity relative to the abundance of invasive Ludwigia hexapetala, water flow patterns and other environmental parameters in 7 discrete reaches of the Russian River watershed, supporting Objective 2C and riverine restoration strategies. Completion of the first phase of this study plan will continue through the end of the 2016 growing season (overlapping into the 1st quarter of FY17) to quantify important variables such as weed abundance that peak late in the growing season. In support of Objective 1, we evaluated mechanisms underlying spread of floating aquatic plants in the Delta. A drogue system has been developed that allows continuous position recording after deployment, combined with a transmitter that allows the researcher to retrieve the drogue so long as they are within 2,000 yards of the device. Several trials of this device have been completed, with more planned over the summer. The device can be placed within a floating mat of water hyacinth or other floating plant, which then tracks the movement of the free-floating mat as it responds to wind, wave, and tidal action. Currently, only water hyacinth has been tested. More surveys will be performed to locate South American spongeplant populations for tracking. Surveys for Diarhabda elongata, a biological control agent of the weed tamarisk, were conducted in northern California to determine establishment of the beetle and its geographic distribution a decade after its release. This first survey confirms the establishment of the beetle in tamarisk stands in northern California. However, these findings indicate that spread of the beetle is limited to the original release area and another nearby watershed but no dispersal was observed into other areas infested with the weed. Additional annual surveys are needed to determine if the beetle’s range is consistent across years. Rapidly expanding yellow flag iris populations may negatively impact extensive ecological restoration plans in the Sacramento-San Joaquin Delta and Pacific coast estuaries. To support Objective 1B, ARS scientists in Davis have established collaborations with scientists at California State University Long Beach, and at University of Seville, Spain in the native range, to determine its physiological tolerances and growth dynamics under increased salinity and inundation regimes expected with sea level rise, and impacts on invertebrate food webs. Study sites have been established along salinity and inundation gradients in the Delta – San Francisco Estuary, and GPS mapping of populations to facilitate refinement of experimental design is complete. Additional reconnaissance field surveys are underway along the Pacific west coast, and will be completed by the end of the 2016 growing season (overlapping FY16- first quarter FY17). To support Objective 2 and the development of geospatially-explicit monitoring methods, ARS scientists in Davis completed surveys of twelve plots in Delta areas with and without Brazilian elodea management, utilizing hydroacoustic technology to measure plant height at discrete points associated with plant presence/absence determinations. Biomass data was also collected at discrete points within the plots, to relate plant height to the best measure of abundance. ARS scientists assessed the ability of the NASA water hyacinth tool to detect locations of water hyacinth, and to measure water hyacinth abundance. The science team measured plant biomass and canopy height where the satellite imagery from LandSat had detected the presence of water hyacinth. Under Objective 2B, the water hyacinth planthopper was released at five sites upstream of the Delta between Sacramento and Madera Counties in northern California to support integrated management strategies. Releases in the Delta have been delayed pending regulatory review. The influence of water hyacinth (Eichhornia crassipes) management on aquatic invertebrate communities of the Sacramento-San Joaquin River Delta was measured. Aquatic invertebrate species were sampled before and four weeks after herbicide application. We selected five herbicide treatment locations paired with five locations where no herbicides were used. Data indicates that seasonality has a stronger influence on invertebrate abundance and diversity measures than weed management activities. The abundance of invertebrates per plant collected four weeks after treatment continued to increase over time but was not different between control and treatment locations. Neither species richness nor evenness was different before and after treatment. The primary community-level difference noted before and after treatment was a significant rise in the number of predators present after treatment. These findings are important for informing management decisions surrounding aquatic vegetation and how management may impact littoral food webs. The impacts of current control activities appear to be minimal for invertebrate species associated with water hyacinth. These findings are useful given the urgency for aggressive water hyacinth management in the Delta and indicate that current management practices are not strongly influencing Delta invertebrate food webs In support of Objectives 1 and 2, the subordinate Delta Regional Areawide Aquatic Weed Project made significant progress on integrated, adaptive management of water hyacinth, Brazilian waterweed and arundo in the Sacramento-San Joaquin Delta. Satellite images from NASA indicated 60% reduction in water hyacinth coverage between July and November 2015, and a 50% reduction in peak annual coverage between 2014 and 2015. The Division of Boating and Waterways-California Department of Parks and Recreation treated a record number of acres of water hyacinth, and improved control of Brazilian waterweed with no additional chemical use. Water hyacinth site selection was guided by implementation of the Water Hyacinth Mapping Tool developed by the Areawide team. In ARS-led seasonal growth studies of water hyacinth, egeria, and curlyleaf pondweed, peak biomass occurred in late-summer/early-fall. Changes in growth and biomass were tied to air and water temperature. Releases of a biocontrol agent for water hyacinth and two for arundo were initiated. ARS and University of California-Davis collaborators performed tests of the effectiveness/efficacy of two existing and two newly-permitted herbicides. The Areawide project team refined a model (Delta Soil and Water Assessment Tool, or Delta-SWAT) to predict weed population growth based on land use. Project collaborators found that egg and larval mosquito densities were elevated in water hyacinth. The UC-Davis Agricultural Issues Center determined the annual cost to control aquatic weeds in the Delta (over $8 million) and constructed an economic model to predict reduced costs in the future. To support Objective 3, studies on dispersal of spotted wing drosophila (SWD) were developed with scientists from University of California, Berkeley. A laboratory colony of SWD was established in Albany, California and permits are pending for the study of three SWD parasitoid species that may be used as biological control agents of the pest. Focus on brown marmorated stink bug was proposed in the Project Plan, but the pest has not reached high densities in California's agricultural systems. In contrast, Bagrada hilaris has rapidly become a major pest of cole crops in the western U.S. To prepare for host range testing of bagrada bug parasitoids to be received this year, laboratory cultures of bagrada bug and six candidate stink bug species were established. Methods were tested for deploying bagrada bug eggs to assess attack by resident natural enemies in the field, and collaborations have been developed with ARS - Stoneville, Mississippi, ARS European Biological Control Laboratory, University of California Cooperative Extension, University of California, Davis, and California Department of Food and Agriculture.

Accomplishments

None.

Review Publications
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.
Duffy, W.G., Garone, P., Grewell, B.J., Kahara, S.N., Fleskes, J., Helm, B., Moyle, P.B., Records, R., Silveira, J. 2016. Wetlands. In: Mooney, H. and Zavaleta, E., editors. Ecosystems of California: A Source Book. Berkeley, CA: University of California Press. p. 669-692.
Grewell, B.J., Skaer Thomason, M.J., Futrell, C.J., Iannucci, M., Drenovsky, R. 2016. Trait responses of invasive aquatic Ludwigia congeners (Onagraceae): effects of ploidy and resource availability. AoB Plants. 8:plw014. doi :10.1093/aobpla/plw014.
Fleming, J.P., Dibble, E.D., Madsen, J.D., Wersal, R.M. 2015. Investigation of Darwin’s naturalization hypothesis in invaded macrophyte communities. Biological Invasions. 17(5):1519-1531.