Host Specificity and Suitability of Lema Cyanella (Coleoptera: Chrysomelidae), a Candidate for the Biological Control of Canada Thistle (Cirsium Arvense)

The host specificity of Lema cyanella (L.) (Coleoptera: Chrysomelidae) and its suitability as a biological control agent were investigated. The females lay an average of 1564 eggs and development from egg to adult takes 17.6 days at 25°C during the day and 20°C during the night (average about 23°C). Feeding of adults and larvae is confined to Cirsium , Carduus , and Silybum species, and according to literature records, Cirsium arvense (L.) Scop. is the main host. No economic plants are attacked. A colony of field collected beetles imported from Germany was infected with a Nosema disease. It is recommended that disease free L . cyanella should be released against the weed C . arvense in North America.