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

2020 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
Understanding how invasions of exotic species begin and progress through space and time is a fundamental objective of invasion ecology and biological pest control research. The focus of this project is to understand how invasions occur, which will provide an ecological foundation for management to disrupt the spread of exotic pests. Identifying plant traits that facilitate colonization of invasive species in new environments can support effective containment strategies prior to rapid population growth. Under Sub-objective 1A, research was completed on measuring the effects of watershed variables on invasion of Ludwigia hexapetala from shoot fragments, resulting in three published journal articles in prior years. ARS researchers at Davis, California, and collaborators, extended this work, with new focus on an understudied reproductive mode: resprouting of Ludwigia congeners from rhizome fragments. Analyses of plant traits grown from rhizome fragments under contrasting soil nutrient levels were completed. L. peploides had superior ability, relative to L. hexapetala, to maximize resource uptake and allocation, that in turn supported rapid colonization. Both taxa exhibited high regenerative ability from rhizome tissue with elevated soil nutrients. This research indicates that reduced nutrient loading and prevention of erosion, which fragments and disperses weed rhizomes, will reduce the weed’s invasive potential. Published results were recognized by an Editor’s Choice award by AoB Plants journal. Also supporting Sub-objective 1A, drift data analyses were completed for water hyacinth and South American spongeplant, and a manuscript was submitted to complete this research. Researchers found direction of tidewater flow was the dominant factor controlling movement, rather than wind direction, as had been found in other studies. Also, in the absence of flood flow events, movements were relatively short in both time and distance – about 2.5 hours and 500 meters, respectively. The size of the mat or clumps of plants had no effect on distance or time traveled. Plants would intermittently snag on obstructions or the channel side during their drifting events, as indicated by an analysis of their global positioning system (GPS) tracks. This research supports the idea that nuisance plants are mostly resident in a given part of the water body, moving only short distances, but this movement can be frequent. Supporting Sub-objective 1B, ARS researchers and collaborators made progress on experimental analyses to assess yellow flag iris growth and trait responses to increasing salinity and inundation with sea level rise. Lab analyses of plant tissue were completed; statistical analyses and a draft manuscript are underway. In field studies comparing phenology and fitness of iris populations, progress was made but greatly constrained due to COVID-19. Dispersal of floating seeds is the primary mode of spread of the species. Trials were completed on germination dynamics of seed sources from fresh vs. brackish tidewater sites in the San Francisco Bay-Delta Estuary subjected to salinity ranging from fresh to marine levels. Higher brackish salinity inhibited germination, but seeds exposed to seawater for 55 days germinated when exposed to freshwater. Results update risk assessments to consider invasion and new colonization of yellow flag iris following potentially long-distance seed dispersal with tidal currents. A manuscript was submitted for publication. Invasive species arriving in novel environments encounter new climatic conditions that affect their establishment. Determining trait responses of invasive plants from different environments provides a framework to assess potential responses to climate change. Supporting Sub-objective 1B, an international team led by ARS scientists at Davis, California, completed an experiment growing an invasive water primrose sourced from six populations and three climatic regions. Populations from geographically distant and climatically distinct regions had the most distinct fitness responses. The more similar the environment in the seed source region was to the newly invaded region, the better the plants performed under new conditions. Results provide new insights to understand colonization of invasive plant species under changing environmental conditions. Findings were published in American Journal of Botany featured with a cover photograph and an Editor’s Choice award. In support of Objective 2, progress was made to improve monitoring of spatially-specific adaptive and integrated management of aquatic weeds and ecological restoration. As a product of the Delta Region Areawide Aquatic Weed Project (DRAAWP), 13 manuscripts were prepared for a special journal issue covering: operational aquatic weed control, seasonal weed growth in the Sacramento-San Joaquin Delta, aquatic weed growth models, efficacy of new chemical control tools, economic modeling indicating cost savings with early-season treatment, effects of water hyacinth on dissolved oxygen and benefits of control, tidal-driven movement patterns of water hyacinth, remote sensing of floating aquatic weeds using satellites, and development of new biocontrol tools. From more narrow-focused beginnings, the DRAAWP broadened impact by implementing new technology reducing water hyacinth by 30%, and improved control of four floating and five submersed aquatic weeds, while leveraging expertise and new funding across 18 public agencies. Under Sub-objective 2A, ARS researchers in cooperation with California State Parks, assessed submersed herbicide treatments to control submersed invasive plants, with focus on Brazilian waterweed. Results clearly demonstrated that hydroacoustic sampling can assess weed abundance in an operational setting, and the management agency has adopted the method for monitoring. Using data generated from these tools and techniques, the effectiveness of submersed herbicide treatments can be statistically evaluated, and provide clear visualization of results for the public. A manuscript reporting results has been accepted for publication. Under Sub-objective 2B, surveys in December 2019 in the Sacramento-San Joaquin Delta indicated the presence of planthoppers at densities of less than one per leaf at eight of 11 sites that had received releases in 2019 for biocontrol of water hyacinth. However, in surveys to determine overwintering in May 2020, planthoppers were found at only three of 11 sites, and only one hopper per site. It was thus not possible to examine the effect of crop pesticide applications, mosquito control or plant quality on planthopper establishment. Four sites with the most stable water hyacinth populations were selected for future planthopper releases. Also in support of Sub-objective 2B, ARS scientists achieved all objectives regarding the effects of herbicide treatment methods for water hyacinth control on invertebrate populations that support endangered Delta fish populations. Published findings provided valuable information for weed management and a framework for reconciling invasive species management efforts that support threatened and endangered Delta fish species. Supporting Sub-objective 2C, ARS scientists evaluated a five-year dataset on temporal and spatial dynamics of riverine plant community distribution, composition, and diversity in invaded patches of Ludwigia hexapetala in the Russian River. Preliminary results indicate these factors vary by river reach, hydrology, and with changing abundance of L. hexapetala. A collaboration for advanced data-modeling, field validations, and manuscript writing were delayed by pandemic constraints. Soil seed banks also affect species composition and restoration of invaded wetland plant communities. Comparisons of similarities in species composition between standing vegetation and a seed bank emergence assay among invaded and non-invaded wetlands were completed. Plant species richness and diversity were substantially lower in standing vegetation at invaded sites as compared to non-invaded sites. Seed bank emergence was recorded in response to drawdown vs. flood inundation, and sediment depth. Over 12 months, 69 plant taxa, including L. hexapetala, germinated primarily from moist soil seed banks signaling the need for long-term management to deplete undesirable seed banks for restoration success. Results were published in a peer-reviewed journal. In support of Objective 3, ARS scientists completed a one-year study examining the effects of habitat fragmentation on populations of spotted wing drosophila (SWD) and its natural enemies in cane berry (raspberry or blackberry) fields in and near Watsonville, California. Every three to four months SWD and its parasitoids were trapped at 52-58 sample locations that varied in the amount of non-crop vegetation surrounding them. Studies continued on bagrada bug (Bagrada hilaris), which is a key pest of cole crops. Abundance and natural enemies of bagrada bug were monitored from summer to fall at 13 sites in northern California by counting numbers and by deploying eggs in patches of known weedy hosts of the bug, adjacent to cole crops. Two species of bagrada bug parasitoids from Pakistan are also being tested. Parasitoids already resident in California were also tested for their ability to attack bagrada bug eggs. New work on tritrophic interactions between the herbivorous bagrada bug, invasive perennial pepperweed, and a plant pathogenic fungus was also conducted and published this year.

Accomplishments
1. New assessment technology improves evaluation of aquatic weed management success. A set of assessment tools developed by an ARS scientist in Davis, California, evaluate control methods for submersed aquatic weeds such as Brazilian waterweed. These tools collectively provide a rigorous test of the effectiveness of weed management actions and related changes in species composition of native plant communities. California State Parks is now using the tools to support adaptive decision making. The tools predict the need for weed control, and quantify the effectiveness of actions taken to reduce weed impacts. Output from these tools also provides an effective way to communicate results to regulatory agencies, as well as to stakeholders and the public.

2. Discovery of traits supporting colonization of invasive water primroses improves management. Understanding plant characteristics that influence spread can be key to improving invasive plant management. Polyploidy is a chromosomal mutation that can drive speciation and potentially increase invasiveness. ARS researchers at Davis, California, and John Carroll University collaborators, applied a trait response framework in outdoor experiments, evaluating responses of diploid and polyploid water primroses (Ludwigia species) to contrasting environmental conditions when established from asexual fragments. Contrary to predictions, the diploid creeping water primrose established from either shoot or rhizome fragments produced more biomass than the decaploid primrose at the colonizing life stage. Results support ploidy-specific management approaches, with priority for early and rapid control of creeping water primrose given the superior colonizing ability of the diploid. Results have also influenced changes in unsuccessful management approaches for different water primrose species that previously had been treated as the same.

3. Discovery of a biocontrol agent that can attack bagrada bug eggs in soil. Bagrada bug has become one of the most damaging pests to cole crops in California after its discovery in the state in 2008. Conventional pesticides are the primary means for controlling this pest, leaving organic growers with few options. A long-term solution is the introduction of a novel biological agent specialized on this pest. Unlike most stinkbugs, bagrada bug buries its eggs individually in soil, and this habit may make it difficult to control. No stinkbug parasitoids that are currently present in California appear to be able to find and attack buried bagrada bug eggs. ARS researchers in Albany, California, found that a parasitoid from Pakistan was able to locate and attack bagrada bug eggs in soil. This ability is likely to be highly specialized, and shows that this parasitoid has potential for helping to control bagrada bug and thereby protect cole crop production in California.

Review Publications
Grewell, B.J., Futrell, C.J., Iannucci, M., Drenovsky, R.E. 2019. Resprouting potential of rhizome fragments from invasive macrophyte reveals superior colonization ability of the diploid congener. AoB Plants. 11(6). https://doi.org/10.1093/aobpla/plz071.
Gallego-Tevar, B., Peinado, P., Alvarez, R., Gandullo, J., Grewell, B.J., Figueroa, E., Castillo, J.M. 2019. Changes to the functional traits of phosphoenolpyruvate carboxylase following hybridization in C-4 halophytes. Physiologia Plantarum. 169(1):83-98. https://doi.org/10.1111/ppl.13053.
Gallego-Tevar, B., Grewell, B.J., Futrell, C.J., Drenovsky, R.E., Castillo, J.M. 2019. Interactive effects of salinity and inundation on native Spartina foliosa, invasive S. densiflora, and their hybrid from San Francisco Estuary, California. Annals Of Botany. 125(2):377-389. https://doi.org/10.1093/aob/mcz170.
Gallego-Tevar, B., Grewell, B.J., Figueroa, E., Castillo, J.M. 2019. The role of exotic and native hybrids during ecological succession in salt marshes. Journal of Experimental Marine Biology and Ecology. 523:151282. https://doi.org/10.1016/j.jembe.2019.151282.
Grewell, B.J., Gillard, M., Futrell, C.J., Castillo, J.M. 2019. Seedling emergence from seed banks in Ludwigia hexapetala invaded wetlands: Implications for restoration. Plants. 8(11):451. https://doi.org/10.3390/plants8110451.
Infante-Izquierdo, M.D., Gallego-Tevar, B., Sanchez-Gullon, E., Nieva, F.J., Grewell, B.J., Castillo, J.M., Munoz-Rodriguez, A.F. 2019. Morphological and anatomical evidence supports differentiation of new interspecific hybrids from native Spartina maritima and invasive S. densiflora (Poaceae, subfamily Chloridoideae). Plant Systematics and Evolution. 305(7):531-547. https://doi.org/10.1007/s00606-019-01591-5.
Hougardy, E.H., Hogg, B.N., Wang, X., Daane, K. 2019. Comparison of thermal performances of two Asian larval parasitoids of Drosopihila suzukii. Biological Control. 136. https://doi.org/10.1016/j.biocontrol.2019.104000.
Infante-Izquierdo, M.D., Castillo, J.M., Grewell, B.J., Nieva, F.J., Munoz-Rodriguez, A.F. 2019. Differential effects of increasing salinity on germination and seedling growth of native and exotic invasive cordgrasses. Plants. 8(10):372. https://doi.org/10.3390/plants8100372.
Hougardy, E.H., Wang, X., Hogg, B.N., Johnson, M.W., Daane, K.M., Pickett, C.H. 2020. Current distribution of the olive psyllid, Euphyllura olivina, in California and initial evaluation of the parasitoid Psyllaephagus euphyllurae as a biological control candidate. Insects. 11(3):146. https://doi.org/http://dx.doi.org/10.3390/insects11030146.
Tofangsazi, N., Hogg, B.N., Portman, S.L., Pratt, P.D. 2019. Tritrophic interactions between an invasive weed (Lepidium latifolium), an insect herbivore (Bagrada hilaris), and a plant pathogenic fungus (Albugo lepidii). Environmental Entomology. 48(6):1317-1322. https://doi.org/10.1093/ee/nvz111.
Gillard, M., Drenovsky, R.E., Thiebaut, G., Tarayre, M., Futrell, C.J., Grewell, B.J. 2020. Seed source regions drive fitness differences in invasive macrophytes. American Journal of Botany. 107(5):749-760. https://doi.org/10.1002/ajb2.1475.
Infante-Izquierdo, M.D., Polo-Avila, A., Sanjose, I., Castillo, J.M., Nieva, F.J., Grewell, B.J., Munoz-Rodriguez, A.F. 2020. Effects of heavy metal pollution on germination and early seedling growth in native and invasive Spartina cordgrasses. Marine Pollution Bulletin. 158:111376. https://doi.org/10.1016/j.marpolbul.2020.111376.
Gallego-Tevar, B., Peinado-Torrubia, P., Alvarez, R., Grewell, B.J., Castillo, J.M. 2020. From physiology to salt marsh management challenges with sea level rise: the case of native Spartina foliosa, invasive S. densiflora and their hybrid. Conservation Physiology. 8(1). Article coaa053. https://doi.org/10.1093/conphys/coaa053.
Hofstra, D., Schoelynck, J., Ferrell, J., Coetzee, J., De Winton, M., Bickel, T., Champion, P., Madsen, J.D., Bakker, E., Hilt, S., Matheson, F., Netherland, M., Gross, E. 2020. On the move: New insights on the ecology and management of native and alien macrophytes. Aquatic Botany. 162:103190. https://doi.org/10.1016/j.aquabot.2019.103190.
Gallego-Tevar, B., Grewell, B.J., Drenovsky, R.E., Castillo, J.M. 2019. Transgressivity in key functional traits rather than phenotypic plasticity promotes stress tolerance in a hybrid cordgrass. Plants. 8(12):594. https://doi.org/10.3390/plants8120594.
Caudill, J., Jones, A., Anderson, L., Madsen, J.D., Gilbert, P., Shuler, S., Heilman, M. 2019. Aquatic plant community restoration following long-term management of invasive Egeria densa with fluridone treatments. Management of Biological Invasions. 10(3):473-485. https://doi.org/10.3391/mbi.2019.10.3.05.