thistle tortoise beetle

Thistle tortoise beetle is a small, exotic beetle. It is native to Europe and Asia. It was introduced into Quebec in 1901 and has since spread across the continent. It is now common in the northern United States from Vermont south to Maryland and west to Great Lakes states. It is present but uncommon in the west. It is uncommon but increasing in Minnesota. It was introduced into New Zealand as a control of the non-native Canada thistle. Though effective, it is not used in the United States because it also attacks beneficial native thistles.

Adults are tortoise-shaped, ¼″ to 5 ⁄16″ (6 to 8 mm) long, oval when viewed from above, and convex when viewed from the side. The female is larger than the male.

The upper thoracic plate (pronotum) and hardened wing covers (elytra) are green. The edges are spread out, flattened, and thin, and extend over the head and legs. The front (anterior) edge of the pronotum is broadly rounded. The corners at the base of the pronotum are at right angles. The plate between the wing bases (scutellum) is small and triangular. The front margins of the elytra, when taken together, form a very shallow arc with a strong, brace-like excavation around the scutellum. The upper surface of the elytra is covered with small punctures but is not deeply pitted or wrinkled. There is a small depression on each elytron in the middle on the front margin. Each depression usually contains a small spot or dark shading. The inner margin of each elytron, where they meet (together called the suture) often has dark shading. The underside of the body is black.

The head is completely concealed when viewed from above. The eyes are not notched. The antennae are long but less than half as long as the body. The first five segments are pale, the remainder dark. Segment 3 is distinctly longer than segment 2, and segment 8 is distinctly longer than wide. The antennae are extended when at rest. There is no groove on the underside of the prothorax for them to be tucked into.

The third segment of the leg (femur) is black at the base, orangish-brown at the tip. The fourth segment (tibia), and the last part of leg (tarsus), corresponding to the foot, are orangish-brown. The tarsus has five segments. The fourth segment is very short and is concealed within the broadened tip of the third segment, making the tarsus appear to have only four segments. The last segment bears a pair of well-developed claws.

Total length: ¼″ to 5 ⁄16″

Weedy fields, roadsides, parks

One generation per year: March through September

Adults feed on the underside of leaves, larvae feed on the upperside. They eat round holes in the leaves.

The larvae carry dried fecal matter over their body, presumably as a form of camouflage. The fecal matter is attached to a forked appendage on the last abdominal segment, and is held suspended over the body.

Adults overwinter in tussocks, leaf litter, and moss. The female lays groups of eggs on the underside of leaves near the base of the plant. The eggs hatch in about a week, and the young reach maturity in about six weeks.

Leaves of plants in the Asteraceae (Aster) family, especially thistles Carduus, Cirsium, and Onopordum, but also knapweed and burdock.

Sources

22, 24, 27, 29, 30, 82, 83.

Still uncommon but increasing in Minnesota

Thistle Tortoise Beetle (Cassida rubiginosa)
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Thistle Tortoise Beetle (Chrysomelidae: Cassida rubiginosa) on Leaf
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Cassida rubiginosa
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Cassida Rubiginosa
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LITTLE GREEN BUG[CASSIDA RUBIGINOSA]
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Location: Woodbury, MN

Location: Woodbury, MN

Location: Woodbury, MN