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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

2018 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 (Ludwigia spp.). Colonization experiments are ongoing but analyses of data from net-captured buoyant fragments at cross-channel transects in five watershed reaches of the Russian River were completed. Unexpectedly, dispersing propagule pressure was nonlinear, with more shoot fragments captured in the middle rather than lower river. Fragments from the middle river were twice the length of fragments captured in the lower river and bore 83% more stem nodes, characteristics associated with greater establishment success. Highly variable capture counts suggest the importance of local pulse disturbance events in dispersal of L. hexapetala. Results support development of spatially targeted management and outreach prevention efforts to decrease propagule dispersal and spread. Results were published, in addition to a second paper reporting germination experiments. In support of Objective 1, ARS scientists implemented a third year of drogue tracking to study factors driving the drift of water hyacinth and South American spongeplant in the Sacramento/San Joaquin River Delta. Tracking studies were performed monthly to supplement data from locations collected during the first two years. Preliminary analysis indicates that water flow due to tidal exchange and sporadic mass flow (e.g., runoff) from tributaries is much more important than wind in moving plant mats, and plant mats typically travel only short distances. The size of the mat had no impact on the distance or direction the mat traveled. Preliminary results were presented at a scientific meeting. Over a decade has passed following the release of Diorhabda carinulata and D. elongata, but the resulting establishment and distribution of these two biological control agents remains unknown. Supporting Objective 1, scientists conducted surveys of the exotic saltcedar trees in California, revealing that beetles remain established in saltcedar-dominated watersheds but their spread is limited to the original release area and another nearby watershed. No beetle dispersal into nearby areas infested with the tree was observed. 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, in contrast to other areas where the beetles are considered successful. These findings indicate that environmental or behavioral factors limit the long range spread of the biological control agent in California. A publication documenting these results has been submitted to a peer review journal. 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 Estuary") and University of Seville to quantify ecological impacts, and assess tolerance and growth with increases in salinity and inundation regimes. In 2018, a United States Geological Survey scientist, with expertise in hydrologic evaluation, joined the collaborative team to assist with elevation surveys and hydrologic analyses. Plant and soil data were evaluated from six population sites along an estuarine gradient. Benthic invertebrate samples were evaluated from four populations. Importance of spread by seed was confirmed, prompting refinement of research plans. Seeds were collected, germination trials were initiated to evaluate thresholds relevant to sea level rise, colleagues began refining experimental designs, and seedlings are being cultured for upcoming manipulative experiments. To support Objective 2, ARS scientists collaborated with the National Aeronautics and Space Administration (NASA) Ames Research Center on simultaneous collection of remote sensing data and ground-collected biomass data to develop a tool to predict the abundance of water hyacinth from LandSat reflectance data. Thus far, the tool can predict biomass in large stands. ARS scientists are also working with cooperators from California State Parks Division of Boating and Waterways to transfer technology on sample methods for species composition in submersed and floating vegetation. Development of a remote sensing tool based on hydroacoustic surveys of sites with Brazilian waterweed has continued. Evaluation of two management demonstration projects is underway using the point intercept sampling method for species composition and comparison of hydroacoustic surveys to ground-truth abundance sampling for target weed biomass. Under Objective 2, releases of the water hyacinth planthopper, M. scutellaris, and the water hyacinth weevil, Neochetina eichhorniae, were permitted, pioneering the inclusion of biocontrol in an integrated, adaptive aquatic weed management plan for the Sacramento-San Joaquin Delta. This plan was facilitated by interagency interactions developed as part of the USDA-ARS-funded Delta Region Areawide Aquatic Weed Project (DRAAWP). The planthopper was released at 20 sites in the Delta. Host range testing of the water hyacinth weevil was completed in quarantine, necessary because a new accession of the weevil from Australia will be released. This accession showed twofold greater reproduction and survival under simulated cold Delta winter conditions as compared to a U.S. and Uruguayan accession. A U.S. accession of the water hyacinth moth, Niphograpta albiguttalis, was obtained and propagated in quarantine for verification of pathogen-free colonies and future field release. Herbicide treatments for water hyacinth control in the Delta are applied in strips, producing areas of mixed decaying and living vegetation. In support of Objective 2, scientists sampled invertebrates per gram of water hyacinth biomass before, and four weeks after, glyphosate applications in treated and untreated areas to determine if decaying plants sustained invertebrate communities. Data suggests more invertebrates occur at all sites after treatment but there was no difference between control and treated sites in species richness or evenness for either sample period. 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. Results provided valuable feedback for weed management and present a framework for reconciling invasive species management efforts that support threatened and endangered fish species. A publication documenting these findings has been submitted to a peer reviewed journal. Understanding how environmental variation in watersheds influences distribution and spread of invasive plants is essential for restoration of impacted ecological functions. Supporting Objective 2, scientists completed analyses of four-year datasets on distribution and abundance of L. hexapetala and environmental variables at three spatial scales in the Russian River, California. Individual population patches expanded where available light and aqueous phosphorus were elevated relative to uninvaded areas. Invaded patches did not expand unabated; the greatest expansion occurred in the middle river (up to 37%) and lower river (up to 88%). In a surprising contrast, up to 20% contraction of patches occurred above seasonal in-stream impoundments. At reach and watershed scales, increasing variability in hydrologic variables correlated with patch structure and spatial dynamics of the invasion with highest abundance in areas with high relative variation in flow. Findings have been submitted and accepted for publication in a scientific journal, and provide a foundation for development of spatially-prioritized integrated hydrologic and invasive plant management strategies to improve ecological restoration outcomes. In support of Objective 3, ARS scientists continued 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 were trapped along 200 meter (m)-long transects that extended from crop fields into adjacent non-crop habitats containing wild blackberry, a key host of SWD. Sampling continued year-round, every one to two months from May 2017. Brown marmorated stink bug was included in the project plan, but has yet to become a major pest in California. In contrast, the bagrada bug (Bh) has become a key pest of cole crops. Its abundance and natural enemies were monitored at 18 sites in Northern Central California by counting numbers and by deploying eggs in patches of known weedy hosts of the bug, which were adjacent to cole crops. Sampling in crop fields will begin in summer, when the bagrada bug starts leaving weed patches. Two species of parasitoids from Pakistan are being tested for efficacy and safety.

1. Climatic tolerances of two key parasitoids of spotted wing drosophila (SWD) determined. Spotted Wing Drosophila (SWD) is a fly that can cause damage to many fruit crops. Only two parasitoids, Pachycrepoideus vindemiae and Trichopria drosophilae, have been recorded to consistently attack SWD in California. Both attack SWD pupae. ARS scientists in Albany, California, are mass-rearing these species for release against SWD. Trichopria drosophilae was found to be less tolerant of temperature extremes than P. vindemiae, indicating that releases of T. drosophilae should focus on coastal locations in California, whereas P. vindemiae may be more successful inland. Results also showed that the parasitoids could be stored at cold temperatures before mass-releases; pupae of both species survived at high rates (69-100%) when placed in cold storage at 12° Celsius for three months.

Review Publications
Madsen, J.D., Wersal, R.M. 2018. Proper survey methods for research of aquatic plant ecology and management. Journal of Aquatic Plant Management. 56:90-96.
Hogg, B.N., Nelson, E.H., Hagler, J.R., Daane, K.M. 2018. Foraging distance of the Argentine ant in California vineyards. Journal of Economic Entomology. 111:672-679.
Skaer Thomason, M.J., Grewell, B.J., Netherland, M.D. 2018. Temporal and nonlinear dispersal patterns of Ludwigia hexapetala in a regulated river. Wetlands Ecology and Management. 1-14.
Castillo, J.M., Gallego-Tevar, B., Figueroa, E., Grewell, B.J., Vallet, D., Rousseau, H., Keller, J., Lima, O., Dreano, S., Salmon, A., Ainouche, M. 2018. Low genetic diversity contrasts with high phenotypic variability in heptaploid Spartina densiflora populations invading the Pacific Coast of North America. Ecology and Evolution. 8(10):4992-5007.
Gillard, M., Grewell, B.J., Futrell, C.J., Deleu, C., Thiebaut, G. 2017. Germination and seedling growth of water primroses: A cross experiment between two invaded ranges with contrasting climates. Frontiers in Plant Science. 8:1677.
Wang, X., Serrato, M.A., Son, Y., Walton, V.M., Hogg, B.N., Daane, K.M. 2018. Thermal performance of two indigenous pupal parasitoids attacking the invasive Drosophila suzukii (Diptera: Drosophilidae). Environmental Entomology. 47(3):764-772.