18th January 1998

Baffled botanists battle a blunder

By Dr. Dharman Wickremaratne

The genesis of the Salvinia plant can be traced to Brazil. At a time when Salvinia was alien to Sri Lanka, the Department of Botany of the University of Ceylon in 1939 got down some Salvinia plants for an examination from the Royal Botanical Gardens in (UK). From time to time Salvinia plants were brought to Sri Lanka from Kew Gardens or Calcutta since the process of getting them down was both expensive and troublesome. Some plants thus brought to Sri Lanka were released into a canal at Kolonnawa in the hope they would grow there to be collected when needed.

Salvinia brought here for study purposes appears to have slipped from everybody's attention after a short period of time. According to a legend, Salvinia is supposed to have been introduced into the major water bodies in and around Colombo in order to make them look like grasslands so that during the Second World War, Japanese parachutists would land on salvinia and get drowned. The fact that the spread of Salvinia began from Kolonnawa is perhaps known only to the scientists who released this plant into the Kolonnawa canal in 1939.

The Salvinia plant spread fast to the water bodies and fertile paddy fields throughout Sri Lanka becoming a great enemy of agriculture. Several steps taken by the relevant authorities towards its eradication had insignificant success. Although Salvinia plants were removed on a mass scale from water bodies and paddy fields, the menace would spread again after a short period of time.

Reading the gravity of the problem, the Natural Resources Energy and Science Authority (NARESA) of Sri Lanka took the initiative to find a solution. Scientists from the Universtiy of Sri Jayawardenapura were of the view that biological control can be successfully adopted against Salvinia and accordingly a project was launched by NARESA to combat Salvinia using a weevil. NARESA's main role here was to enlist the expertise available in universities, research institutes and various government departments. In addition, NARESA obtained the necessary funds from the Australian Centre for International Agricultural Research (ACIAR) and expertise from the Commonwealth Scientific and Industrial Research Organization (CSIRO). The primary course of action undertaken in this project was the testing, both in the laboratory and in the field, of the effectiveness of Cytobagous Salvinia a weevil which had been used successfully for biological control of Salvinia in Australia as well as in Papua New Guinea.

Says Prof. Priyani Soysa, the Director-General of NARESA, "We found out that Australia had discovered a weevil capable of destroying Salvinia. We decided to bring down this weevil to Sri Lanka in order to control the Salvinia menace. Towards the end of 1980, the Department of Zoology of the University of Kelaniya was entrusted with the responsibility of forging ahead with the proposed project in collaboration with NARESA. Presently the officials involved in this assignment have been successful in controlling the menace by about 85%."

While NARESA and CSIRO provided the necessary guidance and ACIAR the financial support, the University of Kelaniya and the Department of Agriculture got involved in the experimental activities. It was a tiny weevil of Brazilian origin known as cyrotobagous salviniae that was made use of for this gigantic task. The first step in the process of experimentation was to ascertain whether this tiny weevil was likely to pose a threat to other agricultural crops. Three well known Biologists in Sri Lanka, namely Dr. G. Sivanathan, Mr. G. A. Gunatilleke and Dr. Ivor Fernando were involved in the initial experiments relating to this weevil.

Said Dr. Ivor Fernando of the Department of Zoology of the University of Kelaniya "When we commenced the campaign against Salvinia, this water weed had already assumed dangerous proportions. However we wanted to make sure that this weevil will not attack any other plant. Detailed experiments were conducted with this weevil by the quarantine division of the Department of Agriculture at Gannoruwa. These experiments proved that the Citrobagus beetle survives solely on Salvinia and will not attack any other plant of economic importance. Accordingly we decided to release this weevil into the water bodies infested with Salvinia".

Speaking further Dr. Fernando said: "NARESA appointed an Action Committee in this connection which consisted of members from NARESA, the University of Kelaniya, Jayawardenapura and the Departments of Agriculture, and Irrigation. Target locations numbering 132 water bodies which had been completely effected by Salvinia throughout Sri Lanka were selected for the purpose of introducing the weevil. A part of the first consignment of weevil received from Australia was handed over to the Central Agricultural Research Institute at Gannoruwa. Propagation of this weevil was not a difficult task. First of all, this weevil was released into selected water bodies even if they were completely covered by this plant. We were convinced that this weevil was the best remedy."

Most of the water bodies examined before and after the biological control programme showed that they are clear of Salvinia. The campaign launched by NARESA covered areas in and around Colombo as well as in Anuradhapura, Polonnaruwa, Kurunegala, Puttalam, Puliyankulama, Girandurukotte, Maduru Oya, Ampara and Angunakola-pelessa.

While the weevil feeds and survives entirely on Salvinia, its breeding cycle is also dependent on the plant. The larvae of this weevil feed inside the plant while the adult feeds on growing buds. Due to the combined action of both adults and larvae, growth of the plant is arrested at first and then the plant dies and turns brown. After a while the dead plants sink to the bottom of the water body. When the Salvinia plant dies in this manner, most of the weevils will perish in the absence of their usual food plants. However some will survive on a few plants and persist to carry on the goodwork.

Director of Plant protection, Dr. Lakshman Amerasinghe said "Our main objective is to breed this weevil in a proper manner because there are several other locations where the threat of Salvinia still exists. We are in the process of releasing the weevil in places like Mahiyanganaya, Bible and Matale. In short we are prepared to release the weevil into any water body where the Salvinia menace exists, if and when we are informed".

Replying to our question as to whether the Plant Protection Unit would respond in the event of several requests for assistance coming in at the same time, Dr. Amerasinghe said: "We have faced such situations before. What we do is to despatch a consignment of weevils by post. The fact that the weevil can survive for a few days without food and water is a special advantage in moving the weevil to various locations. We hope to continue this campaign more systematically in association with state and community organizations and to completely control the Salvinia menace in Sri Lanka in the near future".

The writer is a General Secretary of the Bangkok based Asia Pacific Forum of Environmental Journalists and Deputy Secretary of the Paris based International Federation of Eco Journalists.

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