Cassida rubiginosa
| Cassida rubiginosa | ||||||||||||
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Cassida rubiginosa , Imago |
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| Scientific name | ||||||||||||
| Cassida rubiginosa | ||||||||||||
| OV Müller , 1776 |
Cassida rubiginosa , the thistle shield beetle , belongs to the family of shield beetles .
Mark
Cassida rubiginosa is about 6–7.5 mm in size. The upper side including the pronotum and wing covers is colored bright green, the underside is black. The outer edge of the wing covers and pronotum often have a narrow yellow border. The wing covers often have a yellow-brown or brown basal triangle and four basal spots, which are sometimes fused to a broad brown border along the wing cover seam, but can also be completely absent. The upper side of the pronotum and the elytra is punctured with coarse dots that are not in clear rows on the elytra, but are distributed irregularly over the surface. The legs and antennae are colored red-brown, the antennae darkened towards the tip. In living animals, the body appendages are usually hidden under the broad, shield-shaped body and are not visible.
Biology and way of life
Cassida rubiginosa feeds on thistles ( Cirsium and Carduus ) or burdock ( Arctium ) species. Other, less often mentioned food plants are knapweed ( Centaurea ) and a variety of other asteraceae (daisy family). The most important forage plant for beetles (adults) and larvae is the field thistle ( Cirsium arvense ). The species has at least one generation per year (monovoltin) in the north of its range and overwinters as an imago. To do this, the beetles leave the food plant in autumn and fly specifically to forests and wooded areas, where they overwinter in the leaf litter. If no suitable wintering habitats are available, the mortality in winter is very high (three out of four beetles). The beetles leave their winter quarters in late spring (March to April) and mate on the food plant. Then the female lays her eggs, preferably on the underside of the leaf. The eggs are laid in a protected clutch with a shell (ootheca), a clutch comprises four to five eggs, often fewer, sometimes only one. Each female lays numerous ooths (over sixty on average) within about three months of her life.
Each oothek is then additionally camouflaged by some given droppings. Like most relatives, the thistle shield beetle has five larval stages.
The larval sheaths (exuvia) of the older larvae stick to the dorsal side, usually together with a more extensive sheath of feces. This protective shield is attached to a long, forked extension at the rear end of the larva. In addition, the larva has two rows of spines on each side. The spines mainly serve as mechanical sensory organs (contact mechanoreceptors); when stimulated, the shield is turned to attack. The shield was described by numerous early naturalists, the first René-Antoine Ferchault de Réaumur as early as 1737. The development time from egg to pupa takes about twenty to thirty days, depending on the temperature. The last larval stage sheds the shield, attaches itself to the plant and pupates there. The adults of the new generation hatch in Germany in midsummer with a maximum in late August.
The larvae belong to the prey animals of the field wasps , which are among their most important predators. In an experiment, a working group of Swiss ecologists showed that wasps prey on beetle larvae more often on exposed thistle plants than on hidden ones. However, the beetles do not take this into account when laying eggs.
distribution
Cassida rubiginosa is widespread in Europe from Scandinavia to the Mediterranean region, it occurs eastward through Siberia to the Russian Far East. It was introduced to North America today (first record: 1902 in Quebec), where it is particularly common in Canada and the USA (in the south to Virginia, western border through Ohio, Wisconsin and South Dakota).
Economic importance
The thistle shield beetle's food plant, the field thistle, is one of the most feared agricultural weeds in the world. Adults and larvae can significantly decimate this species, especially towards the end of the growing season, and greatly reduce the seed set. The thistle shield beetle is therefore an important antagonist of this plant species. It was deliberately introduced into some areas to control the field thistle, such as New Zealand in 2007. The beetles can also fly various phytopathogenic rust fungi in the thistle populations. However, this does not happen mutualistically, because the beetles prefer and thrive better on uninfected plants.
Web links
literature
- Rodney H. Ward (1976): Biological Studies on Cassida Rubiginosa Müller, a Thistle Feeding Shield Beetle . Diss, Virginia Polytechnic Institute and State University. 268 pp.
- Rodney H. Ward & Robert L. Pienkowski (1978): Biological Studies on Cassida Rubiginosa Müller, a Thistle Feeding Shield Beetle . Annals of the Entomological Society of America, Volume 71, Number 4: 585-591.
Individual evidence
- ↑ A. Kosior (1975): Biology, ecology, and economic importance of cassids (Coleoptera, Chrysomelidae, Cassidinae) of the Ojców National Park. Acta Zoologica Cracoviensia 20: 251-393.
- ^ E. Obermaier & H. Zwölfer (1999): Plant quality or quantity? Host exploitation strategies in three Chrysomelidae species associated with Asteraceae host plants. Entomologia Experimentalis et Applicata, 92: 165-177.
- ↑ D. Schenk & S. Bacher (2002): The functional response of a generalist insect predator to one of its prey species in the field. Journal of Animal Ecology 71: 524-531.
- ↑ B. Tschanz, E. Schmidt, S. Bacher (2005): Host plant exposure determines larval vulnerability - do prey females know? Functional Ecology 19: 391-395.
- ↑ Christopher G. Maika & Laurent Lesage (2008): Introduced leaf beetles of the Maritime Provinces, 7: Cassida rubiginosa Müller and Cassida flaveola Thunberg (Coleoptera: Chrysomelidae). Zootaxa 1811: 37-56.
- ↑ Landcare Research New Zealand (editor) (2007): What´s new in biological control of weeds? Issue 59. pdf
- ↑ Andreas Kruess (2002): Indirect interaction between a fungal plant pathogen and a herbivorous beetle of the weed Cirsium arvense. Oecologia Volume 130, Number 4: 563-569, doi : 10.1007 / s00442-001-0829-9