Biological control of parrot’s feather, Myriophyllum aquaticum in temperate biomes

Parrot’s feather, Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), is a popular ornamental plant that has become problematic worldwide, due to its ability to spread easily and turn into an invasive species. Originally from the Amazon basin, parrot’s feather has now spread worldwide and is considered invasive in several temperate regions such as western North America, Europe and South Africa. In the invaded range, parrot’s feather forms dense impenetrable mats which affect stream flow, interfere with irrigation, recreational use and increase the risk of flooding. In addition, it degrades water and habitat quality resulting in reduced native species richness. Recently, biological control programmes targeting parrot’s feather in western North America have been initiated. There are three potential biological control agents worth further investigation. The leaf-feeding flea beetle (Lysathia sp.) and the stem-mining weevil (Listronotus marginicollis) are both native to South America and have been developed for South Africa; the former has been released. The third, a North American native weevil (Phytobius vestitus), was recently identified damaging parrot’s feather in Louisiana. Yet, to be able to use these insects as biological control agents against parrot’s feather, several requirements should be met, such as their ability to perform and survive in a different climate from their original one, as well as to establish any potential to spread onto native non-target plant species. Using Lysathia sp. as model system, host-specificity tests are now underway for closely related species with parrot’s feather as controls. In addition, life-history traits of the insect developing on different plant species, and at different temperatures will be measured. Preliminary results suggest that the more complex the habitat is, the more Lysathia sp. tends to be specific to parrot’s feather, suggesting a narrow ecological host range. With this work we hope to highlight the natural enemy suitability for a novel ecological niche, and try to answer the question of what should be prioritized for testing, safety or efficiency?