Parrot’s feather

Parrot’s feather (Myriophyllum aquaticum) is a semi-submerged aquatic plant, native to South America, that invades in coastal waterways in Eastern Australia. It is usually found on the edges of freshwater bodies such as dams and lakes, as well as in slow-moving waterways and drains.

This sub-project will import from Argentina the promising candidate biocontrol agent for parrot’s feather, the stem-boring weevil Listronotus marginicollis, into an Australian containment facility to undertake host-specificity testing. Species within the Myriophyllum genus are phylogenetically grouped into five sections, and further grouped into four subsections and three clades. Parrot’s feather is grouped into section Pectinatum, which does not comprise any other species present in Australia. Therefore, five representative Myriophyllum species native in Australia from other sections will be selected for testing, with emphasis placed on species with overlapping geographical distribution with the target weed and ease of access.

Colleagues from the Fundación para el Estudio de Especies Invasivas (FuEDEI) in Argentina will obtain all relevant permits for exportation, collect the weevil from the field and organise shipments to Australia. After importation from Argentina and establishment of a culture of the weevil in the containment facility in Australia, the selected native species will be tested using replicated adult feeding and lifecycle completion trials under no-choice conditions. If a non-target species supports development of the weevil in more than two replicates across the no-choice trials, then choice trials with that species will be performed. If the weevil develops on a species in choice trials, then continuation trials will be set-up with that species to fully assess risks.

If one or more of the native Myriophyllum species are shown to support a population of the weevil over several generations in the continuation trials, the culture will be terminated, and this candidate agent will not be pursued further. If, however, the trials demonstrate that the weevil does not pose a threat to the tested native species, a proposal will be developed for testing additional species relevant to the Australian context to gather all necessary information to apply for its release in Australia.

Kumaran Nagalingam of CSIRO is leading this sub-project.

Background

Why is the weed a problem?

While parrot’s feather in Australia does not spread by seeds, because they are infertile since only female plants are present, it can effectively spread by vegetative fragments. The weed can form dense stands in waterbodies which adversely affect water flow and habitats for native species.

How is the weed currently managed?

Physical removal is the main control technique used. Where possible, draining of waterbody can be effective in killing the weed as it dries out. Herbicidal treatment is possible, but since the weed is in waterways only limited options are available.

For more detail see https://weeds.dpi.nsw.gov.au/Weeds/ParrotsFeather

Previous research

The stem-boring weevil Listronotus marginicollis, originating from South America, was tested for host-specificity by South African colleagues and shown to only attack Myriophyllum aquaticum. In those tests, however, only one other Myriophyllum sp., M. spicatum, was included since South Africa does not have native Myriophyllum spp. (I. Paterson and G. Martin, Rhodes University, pers. comm.). Despite being shown to be specific and damaging on the weed during testing, a decision was made not to release the weevil in South Africa because the introduced leaf-feeding beetle (see below) is so damaging across the range of the weed and thus there was limited chance that the weevil would establish.

The leaf-feeding beetle Lysathia n. sp., also from South America, was released in South Africa in 1994 for the biocontrol of parrot’s feather. The beetle was found in the host-specificity testing performed prior to its release in South Africa to only attack the target weed and not another introduced, closely related species, Myriophyllum spicatum. However, in subsequent tests performed in South Africa in 2014 for a New Zealand agency interested in this biocontrol agent, the beetle was found to feed and pupate on the New Zealand native Myriophyllum robustum, a close relative of the target weed. Based on this result and considering that Australia has 37 endemic species of Myriophyllum, this candidate agent was not selected for research in this sub-project because of the high likelihood that it would not have the level of host specificity required for the Australian context. While there is no certainty, it is expected that the stem-boring weevil, which is the focus of the sub-project, would be more specific than the leaf-feeding beetle.

Trust-funded sub-project

The key activities of the sub-project are to:

• Import the stem-boring weevil into an Australian quarantine facility and establish/maintain a culture.
• Conduct replicated no-choice trials with the weevil with each of five non-target species closely related to the target weed. Depending on results perform subsequent choice/continuation trials.