Project title: Foreign Exploration in India for Natural Enemies of the Aquatic Weed Hygrophila polysperma, a Recent Invader of Florida’s Freshwater Ecosystems
Contact information:
James P. CudaEntomology & Nematology Dept, UF/IFAS
Building 970, Natural Area Drive
Gainesville, FL 32611-0620
Phone: 352-392-1901 x 126
Fax: 352-392-0190
Email: / William A. Overholt
Biological Control Research and Containment Laboratory UF/IFAS/IRREC
2199 South Rock Road
Fort Pierce, FL 34945
Phone: 772-468-3922 x 143
Fax: 772-468-3973
Email: / Carol A. Ellison
CABI Europe – UK
Silwood Park
Buckhurst Road
Ascot, Berks
United Kingdom SL5 7TA
Phone: +44 (0)1491-829165
Fax: +44 (0) 1491-829123
Email:
Abstract
Hygrophila, Hygrophila polysperma (Roxb.) T. Anderson (Polemoniales: Acanthaceae), is an invasive aquatic plant that is impacting canals, creeks and slow flowing rivers in the lower two-thirds of the Florida peninsula. It is replacing hydrilla, Hydrilla verticillata (L.f.)Royle Hydrocharitaceae), in many waterbodies in South Florida previously infested with this aquatic weed because hygrophila is largely unaffected by conventional herbicides and grass carp used to control hydrilla. Due to the current lack of reliable and cost-effective control measures, the further expansion of hygrophila in Florida is of significant concern. Hygrophila is a serious threat to all Florida waterways because it is capable of tolerating a wide range of water temperatures, and the seeds or viable fragments it produces can be transported unintentionally to new locations. Recent experiences in south Florida indicate that practical solutions for long term control of this plant are not currently available. New methods to control current infestations and prevent further spread are needed to address the hygrophila problem in Florida.
There is general agreement that hygrophila is a good candidate for classical biological control. It is native to the Indian subcontinent, and the risk for non-target damage by approved biological control agents discovered in hygrophila’s native range would be low because only one native species in the genus Hygrophila occurs in the USA. Classical biological control also is an appealing option because the aquatic habitats infested with hygrophila are relatively stable ecosystems conducive to biological control agent establishment. More importantly, the invasive characteristics exhibited by hygrophila are consistent with the ‘enemy escape hypothesis’, which asserts that hygrophila is able to attain high population densities outside its native range because it has been freed from the effects of the coevolved natural enemies that normally keep it in check. Surveys for host specific natural enemies of hygrophila in its native range are needed because there currently is no information available on potential biological control agents of this nuisance aquatic plant. India has a strong interest in biological control and the proposal provides an opportunity to engage and collaborate with India Scientists. This will enable data on the biological control potential of hygrophila to be gathered and incorporates capacity building for Indian students in this approach to weed management.
Project Description:
Hygrophila polysperma (Roxb.) T. Anderson (Polemoniales: Acanthaceae) is a rooted submersed or emersed aquatic plant of shallow freshwater areas and saturated shorelines. Also known as hygrophila, hygro, East Indian hygro, green hygro, Miramar weed, oriental ludwigia, and Indian swampweed, this invasive aquatic plant (hereafter referred to as hygrophila) is a federal listed noxious weed (USDA 1983), a state listed Category II prohibited plant (FLDEP 1993), and a Florida Exotic Pest Plant Council Category I invasive species (FLEPPC 2005). Hygrophila is causing serious problems in many locations formerly occupied by hydrilla, Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae) (Sutton 1995). The submersed growth habit displaces native vegetation in many canals and drainage ditches in south Florida. The plant forms dense stands that occupy the entire water column, clogging irrigation and flood-control systems (Schmitz and Nall 1984, Sutton 1995) and interfering with navigation (Woolfe 1995). It also is capable of competitively displacing native submersed plants in shallow water (Spencer and Bowes 1985) and river ecosystems (Angerstein and Lemke 1994), and will successfully compete with hydrilla in some flowing water systems (Vandiver 1980, Les and Wunderlin 1981, Anon. 1986, Van Dijk et al. 1986). Hygrophila also creates problems as an emergent plant in some shoreline areas, including rice fields (Krombholz 1996).
Practical solutions for the long term control of hygrophila are not readily apparent. Conventional control measures currently being used to manage existing infestations are costly and do not provide satisfactory control. In south Florida canals, for example, aquatic plant managers have been attempting to use an integrated approach that combines mechanical and/or chemical methods with the triploid grass carp Ctenopharyngodon idella Val (Cuvier & Valenciennes) (Pisces: Cyprinidae) a polyphagous fish that was introduced into Florida in the 1970s primarily for controlling hydrilla (Sutton and Vandiver 1986, Sutton 1995).
Each method has its advantages and disadvantages. Mechanical control may be useful for removing the floating mats, but harvesting increases the number of stem fragments that can be transported to other areas where they can infest new water bodies (Sutton 1995). Established hygrophila infestations also are difficult to control with fluridone, an aquatic herbicide currently registered for hydrilla and the plant apparently is resistant to other herbicides registered for aquatic use (Sutton et al. 1994a & b; Sutton 1996). Endothall provides temporary control of both submersed and emersed forms but regrowth occurs 4 to 8 weeks post-treatment (Sutton 1995). Multiple applications of endothall are required to keep hygrophila under maintenance control (Sutton 1995). Herbicides typically used for controlling hygrophila also are expensive, costing from $988 to $1482 per hectare. Treatment costs are even higher when labor and equipment are included. An extreme case involved the use of fluridone in a flowing water system where sustained control was achieved for 20 months at a cost of $34,580 per hectare (Sutton 1996).
Stocking rates with the herbivorous triploid grass carp C. idella that effectively control hydrilla and other aquatic weed species are inadequate for hygrophila because the plants appear to be unpalatable to the fish. The grass carp will feed to a limited extent on submersed hygrophila in the absence of preferred food plants (Sutton 1995). However, larger fish and stocking rates higher than for other aquatic weed problems must be used (Sutton 1995). The stems and leaves are covered with raised lines or dots that contain accumulations of calcium carbonates formed in the epidermal cell walls that are referred to as cystoliths (Sutton 1995). Because grass carp prefer to graze on the soft tips of young tender plants, hygrophila may be less palatable than hydrilla due to the presence of the cystoliths. More importantly, because grass carp are not selective feeders, they will completely remove all aquatic vegetation in a water body if densities are not precisely controlled. Consequently, they cannot be used in large open water systems.
A combination of factors suggests that in the absence of effective control methods, the northern (and possibly western) range expansion of hygrophila will continue. According to Reams (1950, 1953), hygrophila was established in Richmond, Virginia area lakes for 15 to 20 years where it tolerated freezing temperatures for brief periods. Unlike hydrilla that can only invade aquatic habitats, hygrophila often grows terrestrially along the shore as a ditchbank weed (Spencer and Bowes 1985). The plant has a high growth rate and is capable of rapidly expanding a population ten-fold in 1 year (Vandiver 1980). Rooted nodes of small pieces of the easily fragmented stems have the potential to develop new stands (Les and Wunderlin 1981). Spencer and Bowes (1985) showed that regrowth potential from stem fragments even surpasses that of hydrilla. The lack of seasonal variation in biomass, low light compensation and saturation points, a low CO2 compensation point, and the ability to rapidly change resource acquisition in response to changing environmental conditions also make hygrophila a formidable competitor (Spencer and Bowes 1985, Kovach et al. 1992). Chemical treatments for controlling hydrilla may even contribute to the spread of hygrophila by leaving open areas that are susceptible to invasion by the more herbicide tolerant plant (Schmitz and Nall 1984, Spencer and Bowes 1985, Sutton 1995).
A noticable increase in the number of public lakes and rivers with hygrophila has occurred in Florida since 1990 (Langeland and Burks 1998). Schmitz and Nall (1984) offer several explanations as to why the hygrophila problem in Florida is increasing in severity. These include adaptation of the plant to Florida’s waterways, that hygrophila is only now reaching public water bodies after being cultivated elsewhere, eutrophication of Florida’s public lakes and rivers due to the state’s population growth, and it simply may have escaped detection due to its similarity to alligator weed, Alternanthera phylloxeroides (Mart.) Griseb. (Amaranthaceae).
One of the most important but overlooked explanations for the recent hygrophila problem is simply a lack of host specific natural enemies attacking the plant, which would make it less competitive with native flora. Surveys of the natural enemies of hygrophila are needed because there is no information available on potential biological control agents of this aquatic plant (Buckingham 1994, Pemberton 1996, Cuda and Sutton 2000). However, even if extensive surveys produce few or no promising agents on the target species, the possibility exists that the plant could be controlled with natural enemies collected from one of its close relatives; new encounter theory (Hokkanen & Pimentel, 1984). In India, for example, the larva of an agromyzid fly Melanagromyza sp. (Diptera: Agromyzidae) was discovered boring into the stems of the related Hygrophila auriculata (Schumach.) Heine (Lucknow), visibly damaging the plant (Sankaran and Rao 1972, Sankaran 1990). However, native species of Hygrophila in USA need careful consideration before this approach can be implemented.
Project Objectives
Specific project objectives would include the following:
1. Establish collaboration with research institution(s) in India, and develop a research programme on biological control
2. Catalog and geoposition historical populations of hygrophila from herbaria records
3. Identify populations of hygrophila in several Indian locations
4. Collect and identify natural enemies of hygrophila
5. Develop rearing/culturing methods for candidate natural enemies
6. Apply for permission to the Government of India to export candidate natural enemies and import into quarantine for testing in the USA
Methods
Objective 1. Establish collaboration with research institution(s) in India and develop a research programme on biological control:
We propose to establish a partnership with scientific institution(s) initially in India (and perhaps later in Malaysia) to initiate exploratory surveys for natural enemies of hygrophila. Two of the potential collaborating institutions are CABI, which has an office in New Delhi, and the Project Directorate for Biological Control (PDBC) located in Bangalore. Both institutions have well equipped laboratories with modern scientific equipment and other requisite facilities. Faculty and staff are well trained in modern biological control techniques and local regulatory issues. Dr. R. J. Rabindra, the PDBC Project Director and Dr. Sean Murphy, the current Director of the CABI centre, have expressed interest in collaborating on the hygrophila biological control project. Scientists at PDBC will receive training in natural enemy surveying, collection, isolation and identification, as appropriate.
Objective 2. Catalog and geoposition historical populations of hygrophila from herbaria records
Efforts will be made to visit university and museum herbaria in India which may have collections of hygrophila, and Kew Herbarium in London. The locations of hygrophila specimens found in the herbaria will be mapped to help identify sites for conducting natural enemy surveys. The mapping effort will be conducted by Abhishek Mukherjee, a new Ph.D. graduate student from India hired for the project. Mr. Mukherjee will collaborate with CABI and PDBC researchers in India as well as the UF/IFAS Biological Control Research and Containment Laboratory (BCRCL) in Ft. Pierce, FL. The BCRCL recently established a web-based database for cataloging plant and natural enemy information collected in India that is accessible (to all collaborators?) in real time.
Objectives 3 and 4. Identification and characterization of extant populations of hygrophila and collection of arthropod herbivores.
Based on herbaria records and local knowledge, surveys will be conducted to identify populations of hygrophila in water bodies in the region. Ideally, several populations will be found and characterized (e.g., type of water body; water clarity, depth, and quality, plant morphology and genotype, evidence of herbivory, etc.). Plant specimens will be collected and deposited in Indian and USA? herbaria. Organisms found feeding on hygrophila or causing disease symptoms will be collected, preserved, recorded in the database, identified by taxonomic specialists, and voucher specimens deposited in appropriate Indian and USA institutions. Fungal specimens will also be deposited in the CABI International fungal collection and herbarium. Other aquatic plants found growing near hygrophila also will be sampled as a first step in determining host specificity.
Objective 5. Develop rearing methods for candidate natural enemies
Organisms causing obvious damage to hygrophila leaves, stems or roots will be transported to laboratories or field stations operated by CABI or PDBC, and their biologies studied. Priority will be given to those agents found to attack hygrophila exclusively. Rearing methods will be developed based on their biologies.
Objective 6. Apply for permission to the Government of India to export candidate natural enemies and import into quarantine for testing in the USA
A permit will be applied for from the Government of India. If successful, arthropods and fungal pathogens that appear to be specific to hygrophila, and cause visible damage to plants will be imported under permit into quarantine in Florida (either Gainesville or Fort Pierce) for host range studies.
Deliverables
Annual reports will be submitted to the collaborating institutions summarizing project activities, accomplishments and research findings. Preliminary results obtained during the project’s first year will be presented at scientific conferences and reported in Aquatics, the official journal of the Florida Aquatic Plant Management Society. Significant research findings will be published in peer reviewed journals, and all collaborators will receive co-authorship
Benefits to India
The University of Florida (UF) and North Carolina Agricultural and Technical State University (NCA&T) recently launched a major research, teaching and extension effort in collaboration with two agricultural Universities in India- Acharya N.G. Ranga Agricultural University (ANGRAU) and Punjab Agricultural University (PAU) (See http://international.ifas.ufl.edu/FOCUSWEB/focusjun07001.htm). The joint U.S. India Agricultural Knowledge Initiative: “Sustainable Water Resource Management” was established to enhance water resources in India. Because one of the project’s goals is capacity building in water management, the proposed hygrophila biological control project is consistent with the joint Initiative. By participating in the project, specific benefits to India will include: (a) strengthening and enhancing the training of Indian graduate students (e.g., Mr. Abhishek Mukherjee) by providing assistantships for obtaining graduate degrees at UF, (b) discovering new knowledge by surveying, identifying, and vouchering of aquatic plant specimens and biocoenoses associated with hygrophila in Indian museums, (c) providing Indian students and scientists with practical experience in state of the art techniques and procedures currently used in classical weed biological control programs.