Cassida rubiginosa*
* listed for information only. This insect is known to attack native thistles, is not an approved agent, and is NOT distributed by IWCP.
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Common Name
Thistle tortoise beetle
Weeds Impacted
This beetle attacks a number of exotic and native thistles. Both larvae and adults can significantly impact thistle populations by feeding on foliage.
Insect Description/Field Identification
Adults are green, oval beetles with a hard covering over the body somewhat resembling a turtle shell. They are typically around 7.5 mm (approximately 1/3 inch) long and have black undersides. Larvae are green, 6 mm (1/4 inch) long, with spines on their sides and a forked tail spine. The presence of C. rubiginosa in the field can be detected by a characteristic, “window pane” type feeding damage made by young larvae (see below picture of C. rubiginosa feeding damage to the native thistle, Cirsium brevistylum).
Life Cycle
Females lay eggs in the spring and summer. Larvae are active through late summer, when they pupate and the new adults emerge. New adults feed until late fall, then overwinter in soil litter.
Availability
Because C. rubiginosa feeds on several native and economically important thistle species, it is not approved for biological control. This insect is NOT distributed by IWCP.
References
Winston, R., R. Hansen, M. Schwarzlander, E. Coombs, C. B. Randall, and R. Lym. 2008. Biology and Biological Control of Exotic True Thistles. USDA Forest Service. FHTET-2007-05.
Photo Credit
IWCP staff
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