Biological Control
Common Name | Scientific Name | Released | Effectiveness Nationally |
---|---|---|---|
Crown Weevil | Trichosirocalus horridus | 1990s | did not persist - see below |
Gall Fly | Urophora stylata | 1990s | common |
Receptacle Weevil | Rhinocyllus conicus | 1990s | less common |
Regarding the Crown Weevil, De Biase and others have confirmed that a number of thistle species including both Spear Thistle and Nodding Thistle are hosts for this insect, but in Australia it has only persisted on Nodding Thistle (Morley 2012). The Australian releases were sourced from New Zealand where they are effective on both species of thistle. However the New Zealand population was obtained from Canada which in turned got it's insects from Germany. It is possible that a different biotype, for example from Italy, would be more effective in Australia as suggested by Morley.
The Spear Thistle Gall Fly was recorded in the vicinity of Woodlands Historic Park by Tom Morley in 2012. In 2020 these photos were taken in Weeroona Conservation Zone in a patch of Spear Thistles where the fly was very common.
The Receptacle Weevil was observed in the park in 2019.
While not deliberately introduced, Red-legged Earth Mites probably also help to control Spear Thistle, given that plants while they are small are heavily attacked by the mites.
References
- A. De Biase, E. Colonnelli, S. Belvedere, A. La Marca, M. Cristofaro and L. Smith (2015) Genetic and morphological studies of Trichosirocalus species introduced to North America, Australia and New Zealand for the biological control of thistles. Bulletin of Entomological Research.