Weed Biological Control Status and Options for Sri Lanka

Abstract

Invasive alien plants can cause significant losses in production and biodiversity, and due to the high costs of conventional control, biological control is often the only feasible long-term option for their management. Weed biological control was first attempted in Sri Lanka in 1865, with the introduction of Dactylopius ceylonicus to control prickly pear (Opuntia monacantha). Since then, 10 more biological control agents have been introduced into Sri Lanka to control an additional six weed species. Field surveys were conducted to record invasive weeds in Sri Lanka that had been targets for biological control in other countries to identify possible biological control options for Sri Lanka. Over 70 sites were surveyed, covering eight of the nine provinces. Nineteen weed species that are considered invasive and the target of biological control elsewhere were sighted. Biological control attempts have been initiated in Sri Lanka against six of these species: Chromolaena (Chromolaena odorata), water hyacinth (Pontederia crassipes), two types of prickly pear (Opuntia monacantha, and Opuntia stricta), parthenium weed (Parthenium hysterophorus) and salvinia (Salvinia molesta), with mixed success. Introduced biological control agents were not found in all areas where their target weed species were sighted. Therefore, the re-distribution of some of these agents, as well as the introduction of additional biological control agents for chromolaena, lantana (Lantana camara) and parthenium weed, could be reconsidered, given the priorities attached to these species. During the surveys, four biological control agents that had not been deliberately introduced into Sri Lanka were found on lantana, and one agent was found on Noogoora burr (Xanthium strumarium), presumably having spread from India. However, as lantana is not considered under adequate control, the importation of several other biological control agents that have been released worldwide could be investigated. There are good biological control prospects for numerous other weed species also, including alligatorweed (Alternanthera philoxeroides), Madeira vine (Anredera cordifolia), air yam (Dioscorea bulbifera), mile-a-minute (Mikania micrantha), two types of giant sensitive plants (Mimosa diplotricha and Mimosa pigra), parrot’s feather (Myriophyllum aquaticum) and water lettuce (Pistia stratiotes).