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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

2019 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
Progress was made on all three objectives and their sub-objectives. Understanding how invasions begin and progress through space and time is often unknown, but these are fundamental questions in invasion ecology and biological pest control research. The primary focus of this project is to understand how invasions occur, which supports managing and disrupting the spread of exotic pests. Supporting Sub-objective 1A, ARS scientists at Davis, California, conducted experiments to evaluate establishment of invasive water primrose (Ludwigia peploides) recruited from seed into new environments with climates different from their seed source region. These scientists compared growth, morphological, and physiological trait responses of plants generated from seed sourced from multiple invasive populations in three climatic regions: Mediterranean California, Mediterranean France, and Oceanic France, but grown under common environmental conditions in Davis. Results suggest seed source region was a major factor influencing differences in trait responses among plants. Plants from geographically and climatically distinct source regions had the most differences in trait responses. California individuals accumulated more biomass, flowered earlier, and had higher leaf nitrogen content than Oceanic France plants. Those from Mediterranean France were intermediate in responses. The parental seed source influenced differences in the timing and amount of flowering, which ultimately affects invasion success of the offspring in new environments. Parental life-history greatly influenced observed differences in the extent and timing of reproductive effort that can ultimately influence invasion success. Populations from the same climate zones, in contrast, did not consistently have similar functional trait responses even when grown under the same environmental conditions. These findings indicate that invasive Ludwigia populations have developed unique abilities to thrive under different climate conditions. Also in support of Sub-objective 1A, data collection on the spread of water hyacinth and South American spongeplant in the Sacramento-San Joaquin Delta was completed this year, and geographic information system (GIS) analysis of drift of the floating aquatic plants was initiated. The drift of these two species will be analyzed based on wind speed and direction, and tide stage and direction. Analysis indicates that mat movement is not continuous nor necessarily in the same direction as the previous sampled interval. Mats often experience short movements with periods in which they are presumably caught on an obstruction. Movement will not be simple to predict or describe. The biological control agents, Diorhabda carinulata and D. elongata, were introduced from their native ranges to the western U.S. These beetles were expected to attack invasive saltcedar trees and aid in regional efforts to control the weed. The resulting distribution of these insects in California remains unknown. Supporting Sub-objective 1A, scientists surveyed the exotic saltcedar trees in California, revealing that beetles remain established in saltcedar-dominated watersheds but their range was limited to original release areas and another nearby watershed. No beetle dispersal into other areas infested with the tree was observed. Saltcedar remains a serious problem where the beetles are established, indicating that the insects have not been successful at suppressing the invasive weed, in contrast to other areas where the beetles are considered very effective. These findings indicate that unknown factors limit the long range spread of the insects in California. A scientific report documenting these results was published in a peer review journal this year. Invasive yellow flag iris populations negatively impact native plant communities and tidal wetland restoration projects to enhance fish habitat in the Sacramento-San Joaquin Delta, and in other estuaries in their naturalized range. Under Sub-objective 1B, ARS scientists and collaborators from University of Seville, Spain, made progress on laboratory analyses of plant and soil samples from invaded field sites in California, and from native populations in Spain. Statistical analyses of field and laboratory data were conducted, and potential effects of sea level rise were assessed from patch elevation and inundation modeling. The team completed seed germination trials to evaluate thresholds relevant to sea level rise, and initiated manuscript preparation. A two-year common garden experiment initiated with seedlings, and a full factorial greenhouse experiment are underway to evaluate responses of iris seedlings to salinity and inundation stresses and to evaluate their physiological or genetic capacity to adjust and maintain growth and fitness with changing sea level. In support of Objective 2, progress was made to improve scientific monitoring methods and spatially-specific adaptive management of aquatic weeds, and to support integrated weed management and ecological restoration strategies. Under Sub-objective 2A, ARS scientists from Davis completed data collection on two additional demonstration projects in the Sacramento-San Joaquin Delta. The researchers utilized hydroacoustic sampling, biomass sampling, and point intercept sampling to inform management of aquatic weeds using herbicide technologies that had not been previously used or evaluated in the Sacramento-San Joaquin Delta region (hereafter referred to as “Delta”). Herbicide treatments for water hyacinth control in the Delta are applied in strips, producing areas of mixed decaying and living vegetation. In support of Sub-objective 2B, scientists in Albany, California, sampled invertebrates below water hyacinth plants before, and four weeks after, glyphosate applications to determine if decaying plants supported invertebrate communities. Data suggests more invertebrates occur at all sites as the season progressed, but there was no difference between treated and untreated sites in the number of species. Dissolved oxygen decreased in some treated areas, but to levels unlikely to harm invertebrates. Thus, even decaying water hyacinth serves as habitat for invertebrates that are forage for endangered Delta fish species. The results provided valuable information for weed management and present a framework for reconciling invasive species management efforts that support threatened and endangered fish species. Findings were recently published a peer reviewed journal. Also supporting Sub-objective 2B, evaluations of 2018 releases of the water hyacinth planthopper in the Delta indicated that the planthopper established a population at only one of 18 sites, precluding field evaluations of the effects of agricultural herbicide or mosquito insecticide application. Climatic modeling of the planthopper using CLIMEX software suggested that Delta habitats are marginally suitable. Additional planthopper releases are being made in 2019. Prior studies of Delta field populations of the water hyacinth weevil N. bruchi, and laboratory-simulated climatic effects on the closely-related weevil N. eichhorniae, were used to conclude that an Australian accession of the N. eichhorniae is more suitable for Delta releases than the American accession, and host range testing concluded that the Australian accession is safe for release. Supporting Sub-objective 2C, and to support restoration goals, scientists in Davis, California, completed an assessment of environmental characteristics and processes, and their relationship to the dispersal, abundance, and spread of invasive Ludwigia hexapetala at three spatial scales in the Russian River, California. Detailed results reported in FY18 were published this year in a peer-reviewed journal. This year, scientists made progress on analyses of vegetation data from a final component of the multi-year study. They evaluated aquatic plant community distribution, composition, and diversity in invaded patches of L. hexapetala, finding these factors vary by river reach and with abundance of the invasive species. Scientists evaluated species richness and diversity indices to assess impact of L. hexapetala on vegetation by river reach and year, calculated temporal and spatial changes in beta diversity (plant species turnover rates) between river reaches, and completed an indicator species analysis to determine which species are representative of each reach of the river. These data also identify key native plant species that have persisted in the face of invasion by L. hexapetala. Further statistical analyses are planned, and exploration of new models is underway for assessing impact of the invasion on changes in plant species abundance over both space (river reach) and time. In support of Objective 3, ARS scientists completed a two-year study on dispersal of spotted wing drosophila (SWD) and its natural enemies at 10 organic cane berry (raspberry or blackberry) fields. SWD and its parasitoids were monitored along 150 meter-long transects that extended from crop fields into non-crop habitats. Sampling continued year-round at intervals of one to three months. SWD and its parasitoids are also being trapped at 50 sample locations in berry fields and non-crop habitats to study the effects of habitat fragmentation on SWD. Studies continued on bagrada bug, which is a key pest of cole crops. Abundance and natural enemies of bagrada bug were monitored at 18 sites in northern California by counting numbers and by deploying eggs in patches of known weedy hosts of the bug, which were adjacent to cole crops. Two species of bagrada bug parasitoids from Pakistan are also being tested. Brown marmorated stink bug was also monitored, but it is not yet widespread in California.

1. Areawide aquatic weed project reduces floating aquatic weeds. Non-native, invasive floating aquatic weeds, including water hyacinth, South American spongeplant, waterprimrose, and alligatorweed, consume water resources in the Sacramento-San Joaquin River Delta, block flow, hinder recreational boating, and degrade aquatic and wetland habitats. ARS scientists in Albany and Davis, California, led the Delta Region Areawide Aquatic Weed Project (DRAAWP). A new integrated, adaptive management plan based on modeling, remote sensing, testing of new tools, and assessment of efficacy and economic costs, received regulatory approval and has been implemented in cooperation with the Division of Boating and Waterways, California Department of Parks and Recreation, with contributions from National Aeronautics and Space Administration (NASA)-Ames Research Center, four departments at the University of California-Davis, and three other state or county agencies. Use of the plan has already reduced peak annual water hyacinth populations by 30 percent, while reducing the number of acres treated with herbicides per year by over 50 percent. The plan doubles the number of chemical control tools authorized for floating and submersed weeds, adds biological control of water hyacinth, and expands the focus to cover a total of nine floating and submersed weeds. Project outputs are allowing for more proactive, efficacious, and cost-effective aquatic weed management in this critical water resource nexus.

2. Addition of the herbicide endothall for management of Brazilian Egeria (Egeria densa). For the past decade, the only herbicide available to control Brazilian egeria in the Sacramento/San Joaquin River Delta was fluridone. Prevailing wisdom was that the potassium salt of endothall was not effective for controlling egeria. In outdoor aquatic mesocosm experiments, ARS scientists at Davis, California, demonstrated that applications of endothall achieved 60 percent control and a field demonstration project found 43 percent control after a single treatment. The applied significance of this work is confirmation that multiple treatments of endothall will control egeria in the Sacramento/San Joaquin Delta, and will allow water movement in situations in which the fluridone cannot be used. In support of the Delta Region Areawide Aquatic Weed Project, the use of the potassium salt of endothall has passed regulatory scrutiny and will assist in efforts to restore habitat for the endangered Delta smelt. In addition, endothall has been approved for use in irrigation water, so it may be used closer to irrigation water intakes.

Review Publications
Abbas, A.M., Rubio-Casal, A., De Cires, A., Grewell, B.J., Castillo, J.M. 2019. Differential tolerance of native and invasive tree seedlings from arid African deserts to drought and shade. South African Journal of Botany. 123:228-240.
Gallego-Tévar, B., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Figueroa, E., Ainouche, M., Castillo, J. 2019. Genetic structure of Spartina hybrids between native Spartina maritima and invasive Spartina densiflora in southwest Europe. Perspectives in Plant Ecology, Evolution and Systematics. 37:26-38.
Pratt, P.D., Herr, J.C., Carruthers, R., Walsh, G. 2019. Complete development on Elodea canadensis (Hydrocharitaceae) eliminates Hydrellia egeriae (Diptera, Ephydridae) as a candidate biological control agent of Egeria densa (Hydrocharitaceae) in the U.S.A. Biocontrol Science and Technology. 29(4):405-409.
Gallego-Tevar, B., Infante-Izquierdo, M.D., Figueroa, E., Munoz-Rodriquez, A.F., Grewell, B.J., Castillo, J.M. 2019. Some like it hot: Maternal-switching with climate change modifies formation of invasive Spartina hybrids. Frontiers in Plant Science. 10:484.
Hagler, J.R., Nieto, D.J., Machtley, S.A., Spurgeon, D.W., Hogg, B.N., Swezey, S.L. 2018. Dynamics of predation on Lygus hesperus (Hemiptera: Miridae) in alfalfa trap cropped organic strawberry. Journal of Insect Science. 18(4):12.
Donley Marineau, E.E., Perryman, M., Lawler, S.P., Hartman, R.K., Pratt, P.D. 2019. Management of invasive water hyacinth as both a nuisance weed and invertebrate habitat. San Francisco Estuary and Watershed Science. 17(2):1-19.
Gallego-Tevar, B., Curado, G., Grewell, B.J., Figueroa, E., Castillo, J.M. 2018. Realized niche and spatial pattern of native and exotic halophyte hybrids. Oecologia. 188(3):849-862.
Gallego-Tevar, B., Rubio-Casal, A., De Cires, A., Figueroa, E., Grewell, B.J., Castillo, J.M. 2018. Phenotypic plasticity of polyploid plant species promotes transgressive behavior in their hybrids. AoB Plants. 10(5):ply055.
Turnipseed, R.K., Moran, P.J., Allan, S.A. 2018. Behavioral response of gravid Culex quinquefasciatus, Aedes aegypti, and Anopheles quadrimaculatus (Diptera: Culicidae) to aquatic macrophyte volatiles. Journal of Vector Ecology. 43(2):252-260.
Wang, R., Huachin, C., Luo, Y., Moran, P.J., Grieneisen, M.L., Zhang, M. 2019. Nitrate runoff contributing from the agriculturally intensive San Joaquin River Watershed to Bay-Delta in California. Sustainability. 11(10):2845.
Reddy, A.M., Pratt, P.D., Hopper, J., Cibils-Stewart, X., Cabrera Walsh, G., Mc Kay, F. 2018. Variation in cool temperature performance between populations of Neochetina eichhorniae (Coleoptera: Curculionidae) and implications for the biological control of water hyacinth, Eichhornia crassipes, in a temperate climate. Biological Control. 128:85-93.
Hogg, B.N., Moran, P.J., Smith, L. 2019. Relative performance and impacts of the psyllid Arytinnis hakani (Hemiptera:psyllidae) on nontarget plants and the target weed Genista monspessulana (Fabales:fabaceae). Environmental Entomology. 48(3):524-532.
Wang, X., Hogg, B.N., Hougardy, E., Nance, A., Daane, K.M. 2018. Potential competitive outcomes among three solitary larval endoparasitoids as candidate agents for classical biological control of Drosophila suzukii. Biological Control. 130:18-26.
Wang, R., Chen, H., Luo, Y., Yen, H., Arnold, J.G., Bubenheim, D., Moran, P.J., Zhang, M. 2019. Modeling pesticide fate and transport at watershed scale using the soil & water assessment tool: general applications and mitigation strategies. In: Goh, K.S., Gan, J., Young, D.F., Luo, Y., editors. Pesticides in Surface Water: Monitoring, Modeling, Risk Assessment, and Management. Washington, DC: ACS Publications. p. 391-419.