Thistle tortoise beetle

Cassida rubiginosa, Imago

Cassida rubiginosa, the thistle tortoise beetle belongs to the family of shield bugs.

Mark

Cassida rubiginosa is about 6-7.5 mm. The top including pronotum and elytra is colored bright green, the underside is black. Often, the outer edge of elytra and pronotum yellow to a narrow hem. The elytra often have a yellow-brown or brown Basaldreieck and four Basalflecke which are sometimes fused into a broad brown seam along the elytra seam, but also can be completely absent. The top surface of pronotum and elytra has a puncture from rough points that are not on the elytra in distinct rows, but are irregularly distributed over the surface. Legs and antennae are reddish-brown, angedunkelt the sensor to the tip. In the living animal, the body appendages are hidden mostly under the broad shield-shaped body and not visible.

Biology and life

Cassida rubiginosa feeds on thistles ( Cirsium and Carduus ) or burdock ( Arctium ) species. Other, lesser known food plants are Knapweed (Centaurea ) and a variety of other Asteraceae ( daisy family ). Most important food plant for beetles ( imagines ) and larvae is the creeping thistle ( Cirsium arvense). The species has, at least in the north of their range one generation per year ( monovoltin ) and hibernates as imago. The beetles leave to the food plant in the fall and fly targeted forests and wooded areas, where they overwinter in the leaf litter. If there are no suitable wintering habitats available, the mortality rate (mortality) in winter is very high ( three of four beetles ). The beetles leave in late spring (March to April), their winter quarters and mate on the host plant. Then the female lays her eggs, preferably on the underside of leaves. Eggs are laid in a nest protected with a shell ( ootheca ), a clutch consists of four to five eggs, often less, sometimes only one. Each female lays during his life in the course of about three months, numerous oothecae (on average about sixty).

Each ootheca is then additionally camouflaged by something votes feces. Like most relatives of the thistle tortoise beetle has five larval instars.

The larvae cases ( exuviae ) of older larvae remain on the dorsal side stick, usually along with a broader envelope of feces. This shield is attached to a long, fork -piece extension at the rear end of the larva. In addition, the larva on each side two rows of prongs. The sting serve primarily as a mechanical sense organs (contact mechanoreceptors ), irritation of the shield is facing the attack. The shield have described the first René- Antoine de Reaumur already Ferchault 1737, numerous early naturalists. Development time from egg to pupa takes about twenty to thirty days, depending on temperature. The last larval stage raises the shield down, attaches itself firmly to the plant and pupate there. The adults of the new generation hatch in Germany in mid-summer with a maximum in late August.

The larvae are among the prey of the wasp belonging to their main predators. In one experiment showed a working group of Swiss ecologists that the wasp beetle larvae on exposed thistle plants capture more frequently than hidden. The beetles, however, does not take this into account in their oviposition.

Dissemination

Cassida rubiginosa is widely used in Europe from Scandinavia to the Mediterranean region, he comes eastward through Siberia to the Russian Far East before. Today, he is introduced to North America (first proof: 1902 in Quebec), where he is currently in Canada and in the USA ( in the south to Virginia, western frontier Ohio, Wisconsin and South Dakota) is frequent.

Economic Importance

The food plant of the thistle shield beetle, the creeping thistle heard of the world's most feared agricultural weeds. The feeding of the beetles and their larvae can decimate this way particularly towards the end of the growing season and significantly reduce the seed set strong. Therefore, the species is regarded as a major antagonist of the thistle. It was deliberately introduced to combat the creeping thistle in some areas, so in 2007 to New Zealand. The beetles can also transmit flying different plant pathogenic rust fungi on the thistles. However, the combination is not mutualistic, prefer the beetles and thrive better on uninfected plants.