Water hyacinth, Eichhornia crassipesintroduced to both Australia and Thailand late last centuryis probably the world's worst water weed. It chokes lakes, dams and irrigation channels, increases water loss by evaporation, degrades water quality, obstructs water transport and provides sheltered breeding sites for disease vectors such as mosquitoes.
Until recently, the only control methods have been mechanical or herbicidal. These are expensive, with on-going costs. Now, however, biological control offers the best hope of controlling the weed. Two South American beetles, Neochetina eichhorniae and N. bruchi, feed specifically on water hyacinth and have produced good results in Florida, Louisiana and Sudan. After the initial establishment, biological control costs nothing, and is permanentcoping with regular reinfestation from seeds banks or flood-borne plants.
N. eichhorniae was first released in Australia in 1975 and in Thailand in 1979. While it has had a moderate effect on the growth of the weed in Australia, and some effect in Thailand, there are many sites in both countries where it has had little or no impact on infestations. In Thailand, in particular, there are still vast areas infested by water hyacinth. Recent experience in India and the United States suggests that N. bruchi is a more effective control agent than N. eichhorniae, and that under diverse conditions both species together have a greater impact on water hyacinth than either species alone.
Therefore, this project was set up to:
. increase the level of biological control of water hyacinth in Thailand and Australia (and later elsewhere) by the introduction of N. bruchi to augment and complement the already established N. eichhorniae;
. monitor interactions between the two species after field release; and
. investigate the ecological requirements of the two beetles, especially in relation to plant quality, age, size and location, and climate, and to measure its susceptibility to herbicides used for water hyacinth control.
The commissioned organisation for the ACIAR project is the CSIRO Division of Entomology, which has considerable experience in the biological control of other plants as well as water hyacinthfor example, the Division carried out ACIAR project no. 8722 on the biological control of the giant sensitive plant, Mimosa pigra, using various insects and pathogens. Similar standard methodology will be used in the present project for assessment of weed and control agent populations, spread of agents and control achieved.
A CSIRO entomologist will visit the United States Department of Agriculture (USDA) in Florida to study methods used and work undertaken there with N. bruchi and bring a culture of the beetle back to Australia. N. bruchi will be established in quarantine facilities in Brisbane and Bangkok, and tested for host specificity on a variety of plants. Subject to satisfactory results, the beetle will then be released and monitored (for establishment, multiplication, spread, effect on water hyacinth, and interaction with the already established N. eichhorniae) in both countries. Again subject to satisfactory results, the project team will provide cultures of N. bruchi to other Southeast Asian countries.
The Australian project leader will coordinate the project and collaborate with contacts in Thailand and other Southeast Asian countries established during the M. pigra project. The Thai project leader, from the National Biological Control Research Center, Bangkok, will also liaise with other Asian countries using his large network of contacts in the region.
The introduction of N. bruchi is expected to control water hyacinth effectively in Australia and Thailand, and the researchers expect that economic benefits will start accruing 35 years from the beetle's establishment. It is difficult to put a monetary value on successful control, but an economic assessment of a comparable project on the biological control of salvinia water weed estimated a 50-fold return on project funding of $A300 000.
Apart from reduced application of herbicides to various aquatic environments, benefits will include reduced choking of habitats of aquatic animals by weed masses, reduced obstruction of water channels and water supplies, and reduced health hazards. These benefits will, in turn, flow to other Southeast Asian countries as N. bruchi from Thailand is made available to them.
All countries involved will benefit from the information gained, and the Australian collaboration will enhance the capacities of Southeast Asian countries to conduct their own biological control work in the future.
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