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Biological control of Hygrophila polysperma: Searching for natural enemies in India - First Trip Report

Mukherjee, A. , Cuda, J. P., Overholt, W. A. & Ellison, C.
Entomology and Nematology Department, University of Florida, BioControl Research & Containment Laboratory, University of Florida, CAB International, Silwood Park, Ascot, UK SL57TA. Published in Aquatics (Spring 2008) Vol. 30(1): 20-22

Introduction:

Dr. Jim Cuda and Dr. Carol Ellison in CABI, New Delhi Office
Fig. 1: Dr. Jim Cuda and Dr. Carol Ellison
in CABI, New Dehli Office.

Hygrophila, Hygrophila polysperma (Roxb.) T. Anders (Acanthaceae) is a federal- listed noxious weed, and an invasive aquatic plant in Florida that is spreading to other warm water areas of the United States and Mexico. This plant is 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. Alternative methods are needed to address the hygrophila problem in Florida in order to prevent the rapid regrowth and spread of this aquatic weed.

Meeting in PDBC, Bangalore, India
Fig. 2: Meeting in PDBC, Bangalore, India
Dr. Rabindra (centre) and his team (right)

There is general agreement that hygrophila is a good candidate for classical biological control. The risk for non-target damage by approved biological control agents would be low because only one native species in the genus Hygrophila occurs in the US. Classical biological control is an appealing option because the aquatic habitats infested with hygrophila are relatively stable ecosystems conducive to biological control agent establishment, and the invasive characteristics exhibited by hygrophila are consistent with the ‘enemy escape hypothesis’. Because hygrophila is an Old World species that is native to the southeastern Asiatic mainland (e.g. India), surveys of its natural enemies are needed because there is no information available on potential biological control agents for this aquatic plant. We recently traveled to India in order to establish cooperative agreements with collaborating institutes, and obtain locality information for hygrophila by visiting different herbaria.

Accomplishments:

We arrived in New Delhi (previously Delhi) on 18 September 2007. The following day we met Dr. Carol Ellison (Fig 1.) to discuss specific project objectives. Dr. Ellison, a Senior Scientist and Invasive Species specialist with CABI was hired as project consultant and liaison with the Project Directorate of Biological Control (PDBC) India, an institute of the Indian Centre for Agricultural Research (ICAR) which is the central body of biological control research in India. During the course of this project CABI will be our main contact in India. Dr. Ellison is a Plant Pathologist who will provide expertise in isolating and identifying pathogens affecting hygrophila.

On 20 September, a visit was made to Bangalore, where Dr. Ellison met with Dr. Rabindra, the Director of PDBC (Fig 2.). As the primary organization for biological control research in India, PDBC has well equipped laboratories and field stations for conducting surveys and rearing of natural enemies. A presentation was made containing background information and specific objectives of the project. Dr. Rabindra and his team were impressed by the objectives of the project and assured us of their cooperation

Collection of herbarium information:

Fig. 3 Map showing the distribution of hygrophila (shaded area) in India
Fig. 3 Map showing the distribution of
hygrophila (shaded area) in India.

After reaching Kolkata (previously Calcutta) on 29 September, our primary objective was to collect herbarium records of hygrophila before initiating local surveys. We visited the ‘Central National Herbarium’ located in the ‘The Botanic Garden’, Howrah, Kolkata on 1 October. Established in 1795 by Dr. Willium Roxburgh, ‘The Central National Herbarium’ popularly known as CNH, is one of the oldest and largest herbaria in the world. Currently, the CNH houses about 2.5 million herbarium specimens representing nearly 350 plant families; the specimens are arranged according to Bentham and Hooker’s system of classification. The herbarium Director was kind enough to allow us to access the data base. In total, 64 specimens of hygrophila were examined and the locality information/ecological notes recorded. The herbarium’s records indicated that hygrophila was collected from 12 Indian states, the majority of samples (26 of 64, or 41%) from the state of West Bengal in northeast India. The earliest record dates back to 1910 and at least one sample were collected at an altitude of 1200m. Locality information of hygrophila is presented in Figure 3 (expanded to include Kew Herbarium Records). It is evident from the available data that hygrophila is widely distributed. Contact also was made with the Director of the Herbarium at Kew, London, to arrange a visit to examine their hygrophilacollection. This will help to delimit the distribution of H. polysperma in its centre of origin.

Survey in local aquarium market:

Hygrophila for sale in local market.
Fig 4: Hygrophila for sale
in local market.

Conducting a field level survey based entirely on the herbarium records was difficult due to the time constraint. Therefore, we visited the local aquarium market to find out if hygrophila is being sold commercially. We contacted local aquarium shops and found out that it might be sold in the Sunday ‘Hat’. Hat, in local dialect, is a market that takes place once a week where people from distant places usually come and sell their products, similar to ‘Flea Market’ in the US. We visited the market on 7 October to search for hygrophila. We located a person selling various aquatic plants and were fortunate to find hygrophila among all the different plants being sold (Fig. 4). We purchased some plants from the vendor and also inquired about their location. He agreed to accompany us to those places where he collected the hygrophila.

Identification of Hygrophila polysperma:

Fig. 7: Map showing geo referenced hygrophila population
Fig. 7: Map showing geo referenced
hygrophila population.

Before going into the field to perform the surveys, proper identification of the plant was important. Therefore, we contacted Prof. G. G. Maiti, University of Kalyani, located in Kalyani, West Bengal on 9 October. Dr. Maiti is a plant taxonomist, specializing in biosystematics of angiosperms. He was very helpful to us and confirmed the identification of the plant we collected from the market. Those plants were indeed Hygrophila polysperma.

Local survey for hygrophila:

Geo position of local hygrophila population
Fig 5: Geo position of local
hygrophila population

Insect damage on hygrophila
Fig 6: Insect damage
on hygrophila

The main purpose of this initial survey was to locate an extant population of hygrophila, search for any incidence of insect feeding damage and geo-position the plant’s location (Fig. 5). Collection of the plants for further genetic analysis was another important objective. In this first survey in Kalyani, West Bengal, Prof. Maiti accompanied us on the trip. We were able to locate the plant at Muratpur, Kalyani, West Bengal (labeled as location 1 on the map) along the bank of a canal (Latitude: 22.985375, Longitude: 88.435753) (Figure 7). Since the time of the year when we carried out this survey was just after monsoon season, the main problem that we faced was gaining access to the flooded water bodies. However, it was apparent that this plant grows abundantly in marshy areas of West Bengal. We performed additional surveys (a total of 6 surveys were conducted) around West Bengal to geo-reference the extant population of hygrophila. On the map, another site labeled as location 2 (Fig. 7) was characterized (Latitude: 22.436111, Longitude: 88.394361) having a large patch of hygrophila.

Searching for natural enemies also was part of our initial survey. During the course of our survey we observed some insect feeding damage on the leaves (Fig. 6), but we were unable to collect or identify the natural enemies at this time.

Survey for natural enemies on Hygrophila auriculata: a closely related species of Hygrophila

H. auriculata leaves showing insect damage. H. auriculata leaves showing insect damage.
Fig 8: H. auriculata leaves
showing insect damage.

While in India surveying for natural enemies of hygrophila in September-October 2007, we located another species of the same genus, Hygrophila auriculata (Schum), which is a congener of the target weed. Hygrophila auriculata occurs in the same habitat preferred by hygrophila and thus provided us with an opportunity to survey for genus specific natural enemies. The purpose of this initial survey was to collect samples of H. auriculata and confirm the identity of this species. While collecting the samples, we also found insect damage and disease symptoms affecting the plant. Although we were unable to specifically identify the natural enemies impacting H. auriculata, our findings clearly showed the potential for obtaining insects and pathogens from this congener of hygrophila. There also is published report of larvae of an agromyzid fly boring into the stems of H. auriculata. Additional surveys in 2008 will focus on this natural enemy.

Establishment of a field station:

Establishment of a field station was another important objective of this first trip to India. This field station will be used to establish a culture of pathogens and search for insects before transporting them to the PDBC laboratory in Bangalore for further identification and rearing. It is quite evident from the available data that the eastern part of India is very favorable for the growth of hygrophila. Therefore, having a field station in this particular area will be essential for the success of the project. We were able to establish a cooperative agreement with Krishi Vigyan Kendra (KVK) (= Agriculture Research Institute), Nimpith, West Bengal. KVK is an Indian Council of Agriculture Research (ICAR) affiliated institute that is dedicated to transfer of technology from ‘lab-to-land’. The KVK agreed to provide laboratory space for our use.

Acknowledgements:

Acknowledgements:
This research project is supported by grants from Osceola County, Florida and the Florida Department of Environmental Protection.
For further information on hygrophila use the following references:

[FLEPPC]Florida Exotic Pest Plant Council. 2005. List of Florida’s Invasive Species. Florida Exotic Pest Plant Council. 2005. http://www.fleppc.org/05list.htm.
[USDA – GRIN] United States Department of Agriculture, Germplasm Resources Information Network. Internet: http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?316380