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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

2021 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
This is the final report for Project 2030-22000-029-00D, which has been replaced by Project 2030-22000-032-00D. For additional information, see the new project report. Supporting Sub-objective 1A, scientists at Davis, California, investigated the influence of hydrology on watershed-scale dispersal and spread of Ludwigia hexapetala. Repeated sampling of buoyant, asexual fragments of five sites in the Russian River was completed to assess variation of dispersal with river flow. Results indicate pulse recreational disturbances best explained 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. Published results suggest a need for prioritized weed management in the middle river reach. Under Sub-objective 1A, data acquired using GPS trackers for analyses of drift of were completed to improve understanding of mechanisms underlying the spread of floating water hyacinth and South American spongeplant. Researchers found direction of tidewater flow was the dominant factor controlling movement, rather than wind direction. In the absence of flood flow events, movements were relatively short in both time (2.5 hours) and distance (500 m). The size of the mat or clumps of plants had no effect on distance or time traveled. This research indicates floating weeds are mostly resident in occupied areas, moving only short distances, but this movement can be frequent. Two beetles, Diorhabda carinulata and D. elongata, were intentionally introduced from their native ranges to the western United States for the biological control of saltcedar. Based on success elsewhere in the United States, these beetles were expected to attack invasive saltcedar trees and aid in regional control efforts. Supporting Sub-objective 1A, scientists surveyed saltcedar trees in California to determine the status of control, and found that one beetle is established in saltcedar stands but its range is very limited in California. No beetle dispersal into other infested areas was observed. Saltcedar remains a serious problem where the beetle is established. The insects have not been successful at suppressing the invasive weed in California. Results indicate that unknown factors limit the long range spread of the insects in California. A scientific report documenting these results was published in 2019. Under Sub-objective 1B, an experiment evaluating the growth and trait responses of invasive Iris pseudacorus (yellow flag iris) to increasing salinity and inundation with sea level rise was completed. Iris growth greatly declined in moderate brackish salinity compared to plants grown in freshwater during the pre-reproductive life stage. The weed was tolerant of inundation, but increasing salinity limited its capacity to acclimate to deeper inundation. Germination dynamics of iris seeds from invaded San Francisco Bay-Delta tidal wetlands were evaluated under a range of fresh to marine salinity levels. High brackish salinity inhibited germination, but seeds exposed to seawater for 55 days quickly germinated when exposed to freshwater. Risk assessments should consider colonization potential of yellow flag iris following long-distance tidal seed dispersal. Two articles were published in peer reviewed journals. Under Sub-objective 1B, scientists at Davis, California, and Rennes, France, completed experiments on seed germination of invasive Ludwigia spp. (water primroses) populations from two invaded ranges: California and northwestern France. The germination capacities of L. hexapetala and L. peploides were compared under 3C warming predicted in climate change models. Under all tested temperatures, the germination rates were over 80% for L. hexapetala 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. An experiment comparing seedling performance of Ludwigia spp. sourced from six invasive populations in three climatic regions was performed. Populations from geographically distant and climatically different 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 emergent seedlings performed under new conditions. Published results provide new insights on the colonization of invasive plant species under changing climatic conditions. Under Objective 2, the Delta Region Areawide Aquatic Weed Project (DRAAWP) supported the National Aeronautics and Space Administration (NASA), five University of California departments and four state and county agencies. New adaptive, integrated chemical, mechanical and biological control tools, remote sensing/assessment and modeling were developed by ARS and other project scientists and implemented against four floating and five submersed weeds in the Delta. Products included five scientific symposia, four stakeholder meetings with 15 natural resource agencies and 55 other stakeholder presentations, a project website and blog, and a journal special issue. Outcomes included a 30% reduction of peak annual floating weed acreage between 2015-2018 with a concomitant 50% reduction in herbicide application. Stakeholders experienced 50 to 100% reduced weed control costs in marinas and pumps. Two new interagency working groups leveraged the USDA funds 10-fold to support new aquatic weed control and habitat restoration projects. 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 indicate hydroacoustic sampling can assess weed abundance in an operational setting, and the management agency 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. Under Sub-objective 2B, the water hyacinth planthopper (Megamelus scutellaris) was verified as established in Folsom, California. In the Sacramento-San Joaquin Delta, surveys at 16 sites for leaf-chewing weevils (Neochetina spp), a leaf-mining moth (Niphograpta albiguttalis) and the planthopper revealed that only N. bruchi is broadly established in the Delta and, although genetically diverse, does not provide control. Chilling studies indicated that N. eichhorniae from Australia was tolerant of temperate Delta conditions. Lab tests verified that listed fish species experienced no ill effects from feeding on these insects. A total of 490,000 water hyacinth planthoppers were released in the Delta, and they were found at six sites in December 2020, suggesting establishment. A beetle released previously in the United States was released against alligator weed near the Delta, and three potential agents were evaluated in the lab against water primrose. Regulatory permits dictate that herbicide treatments for water hyacinth control in the Delta be applied in strips, producing areas of mixed decaying and living vegetation. Supporting 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 revealed that invertebrates increased over time, 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. These findings were published a peer-reviewed journal. Under Sub-objective 2C, a 5-year study was completed on how environmental variation influences the abundance and spread of invasive Ludwigia hexapetala in the Russian River Watershed. Abundance was greatest in areas with high variation in flow. Population patches expanded where light and aqueous phosphorus were elevated relative to uninvaded areas. Native plant species persisting with invaders were identified to support restoration approaches. Plant species richness and diversity in vegetation and seed banks were substantially lower in Ludwigia-invaded sites. In a seed bank emergence assay (treatments: moist soil; shallow flood), 4,075 seedlings including 69 plant taxa and 33% alien species, emerged primarily from moist soil signaling the need for long-term effort to deplete weed seed banks for restoration success. Results were published in peer-reviewed journals. For 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. A one-year study was also conducted on the effects of habitat fragmentation on SWD in cane berry fields at over 50 locations. Populations of resident natural enemies were augmented to help control SWD; over 300,000 parasitoids were released. A five-year study was completed on the effects of resident natural enemies on bagrada bug, which is a key pest of cole crops. Each year natural enemies of bagrada bug were monitored from summer to fall at a total of 18 sites in California by deploying eggs in patches of weedy hosts of the bug, which were adjacent to cole crops. The host specificity and foraging efficiency of two species of bagrada bug parasitoids from Pakistan were also tested.


Review Publications
Williams, D.A., Harms, N.E., Knight, I.A., Grewell, B.J., Futrell, C.J., Pratt, P.D. 2020. High genetic diversity in the clonal aquatic weed, Alternanthera philoxeroides in the United States. Invasive Plant Science and Management. 13(4):217-225.
Leon-Osper, M., Infante-Izquierdo, M.D., Soriano, J.J., Nieva, F.J., Grewell, B.J., Castillo, J.M., Munoz-Rodriguez, A.F. 2020. Heat stress effects on sexual reproductive processes of a threatened halophyte. South African Journal of Botany. 133:184-192.
Castillo, J.M., Curado, G., Munoz-Rodriguez, A.F., Grewell, B.J. 2020. Germination syndrome divergence among pairs of sympatric sister species along an estuarine salinity gradient. Environmental and Experimental Botany. 181. Article 104274.
Gillard, M.B., Castillo, J.M., Mesgaran, M.B., Futrell, C.J., Grewell, B.J. 2021. High aqueous salinity does not preclude germination of invasive Iris pseudacorus from estuarine populations. Ecosphere. 12(5). Article e03486.
Daane, K.M., Yokota, G.Y., Walton, V.M., Hogg, B.N., Cooper, M.L., Bentley, W.J., Millar, J.G. 2020. Development of a mating disruption program for a mealybug, Planococcus ficus, in vineyards. Insects. 11(9):635.
Daane, K.M., Wang, X., Hogg, B.N., Biondi, A. 2021. Potential host ranges of three Asian larval parasitoids of Drosophila suzukii. Journal of Pest Science.
Reddy, A.M., Pratt, P.D., Grewell, B.J., Harms, N.E., Cibils-Stewart, X., Cabrera Walsh, G., Faltlhauser, A. 2021. Biological and host range characteristics of Lysathia flavipes (Coleoptera: Chrysomelidae), a candidate biological control agent of invasive Ludwigia spp. (Onagraceae) in the USA. Insects. 12(5):471.
Rayamajhi, M.B., Rohrig, E., Tipping, P.W., Pratt, P.D., Leidi, J.G. 2020. Allometric equations for the invasive vine air potato (Dioscorea bulbifera) in its exotic range in Florida. Invasive Plant Science and Management. 13(2):76-83.
Solis, M.A., Pratt, P.D., Makinson, J., Purcell, M.F., Rayamajhi, M.B., Mattison, E.D., Mally, R. 2020. Archernis humilis (Swinhoe) (Lepidoptera: Crambidae) rediscovered feeding on skunk vine (Paederia foetida L.) in southeast Asia. Proceedings of the Entomological Society of Washington. 122(3):732-749.
Smith, M., Wright, S., Clark, P.T., Pratt, P.D., Purcell, M., Brown, B. 2020. Fundamental host range of Lophodiplosis indentata (Diptera: Cecidomyiidae), the last proposed biological control agent for Melaleuca quinquenervia (Myrtaceae) in Florida. Biocontrol Science and Technology. 30(10):1073-1082.
Wineriter-Wright, S., Smith, M., Metz, M., Makinson, J., Bradley, B., Purcell, M., Pratt, P.D. 2020. The biology of Casmara subagronoma (Lepidoptera: Oecophoridae), a stem boring moth of Rhodomyrtus tomentosa (Myrtaceae): descriptions of the previously unknown adult female and immature stages, and its potential as a biologic. Insects. 11(10):653.