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Thistle tortoise beetle
The thistle tortoise beetle, Cassida rubiginosa, is a tortoise beetle, and as such belongs to the leaf beetles. It has a green carapace (despite "Rubiginosus" being latin for "rusty or rust-coloured").
It is a species recorded in Britain and is native to Eurasia. It feeds on Canada thistle and was intentionally introduced to Virginia to control thistles. It has spread to the northern United States, following accidental introduction to Quebec in 1901. In Canada it has also spread to New Brunswick and Alberta.
Cassida rubiginosa was brought to New Zealand for use as a biological control agent against Canada thistle in 2006. In New Zealand this species is commonly referred to as the 'green thistle beetle' by landowners and biological control practitioners. Field releases of egg-laying adults were first carried out in Otago and Southland in spring 2007. Beetle populations at early release sites in Southland have become established and are already having a minor localized impact on the thistles. It is estimated that Canada thistle (known commonly in New Zealand as 'Californian thistle') costs landowners around $32 million per year in Otago and Southland alone.
Cassida rubiginosa larva carrying package of dried frass on its back
- "Cassida rubiginosa". Integrated Taxonomic Information System.
- "The Biological Control of Weeds Book" Landcare Research/Manaaki Whenua http://www.landcareresearch.co.nz/research/biocons/weeds/book/documents/Green_Thistle_Beetle.pdfInsert footnote text here
- "The Bugs' Informer" http://www.es.govt.nz/documents/brochures/biosecurity/the-bugs-informer-july-2008.pdf
- "Beetles to battle $32m-a-year thistle problem". The Southland Times. Retrieved 22 November 2011.