Grain beetle

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Grain beetle
Female grain beetle (Sitophilus granarius)

Female grain beetle ( Sitophilus granarius )

Systematics
Order : Beetle (Coleoptera)
Family : Weevil (Curculionidae)
Subfamily : Dryophthorinae
Tribe : Litosomini
Genre : Sitophilus
Type : Grain beetle
Scientific name
Sitophilus granarius
( Linnaeus , 1758)

The grain beetle ( Sitophilus granarius ) is a beetle from the family of the weevils (Curculionidae), which probably originally - like the ancestors of today's cereals  - comes from the Near East . It is the most widespread grain pest in Europe and has been proven as early as the early Neolithic ( ceramic band culture ).

features

The beetles have a body length of 2.7 to 3.7 millimeters, also called 2.5-5.1 millimeters. The body is elongated, parallel-edged and slightly flattened. Immediately after the metamorphosis, the beetles are light to red-brown in color, with increasing age the color changes to dark to black-brown. The head continues into a trunk with the mouthparts at the front end. The proboscis of the males is shorter and thicker than that of the females. Because of these differences, the two sexes are easy to recognize from the outside. The two six-part, kneeled antennae have their origin at the base of the trunk. The complex eyes are elongated and arranged behind the antennae. The pronotum is large and has numerous punctiform depressions. The cover wings are as long or slightly longer than the pronotum and completely cover the abdomen. They have a pattern of longitudinal rows of points and ridges that alternate with one another. The beetles are unable to fly because the hind wings have receded. The species can be confused with the rice beetle ( Sitophilus oryzae ), whose pronotum, however, is provided with small, roundish dots and whose stippling of the stripes on the wings is larger and in the interstices more rounded.

Occurrence

The grain beetle is distributed worldwide ( cosmopolitan ) and occurs in Europe in the north to the south of Norway and Finland as well as to central Sweden. The species is also common in the British Isles . Due to the trade in grain, the species, which was probably originally distributed in the Near East, has spread over the entire temperate zone of the earth. Since it does not tolerate tropical and subtropical climates well, it has no economic importance in these parts of the world, but is otherwise a dreaded pest in granaries. There, as well as in mills, the species can occur in huge quantities. They can also be found in dried vegetables.

Way of life

The development of the beetle from the egg to the finished insect takes place within a grain of grain, the rest of life takes place outside. After the beetles have left the grains and the ambient temperature is at least 13 ° C, they mate. The start of egg-laying is also temperature-dependent. At 25 ° C, the females begin to lay eggs about five days after mating. To do this, they pierce the shell of a grain of corn, place an egg in the cavity and close the opening with a secretion that quickly hardens to a whitish plug in the air. This can be easily recognized with a magnifying glass. A female lays an average of 100 eggs, with a maximum of more than 200 eggs. Usually a grain of cereal is only equipped with one egg. If the supply of cereal grains is low, it can exceptionally be two. The eggs are 0.5–0.6 mm long, 0.25–0.3 mm thick, slightly oval, initially colorless, later milky. At 25 ° C, the larvae hatch after about four days. They don't have legs. Three chest and ten abdomen segments can be recognized by the pronounced furrows across the body. The head is brown, the rest of the body white. Pupation begins after 27 days at 25 ° C, and the pupae rest for about eight days. The finished beetles initially remain in their grains, then they drill a hole through the shell, the size of which corresponds to the diameter of the body, and they leave the grains. The size of the beetles depends on the size of the grains in which they develop, the nutritional content of the respective grain types, as well as the ambient temperature and humidity. At 29 ° C and 75% rel. The beetle's lifespan is around five months.

Endosymbiosis

The grain beetles live in symbiosis with thread-like bacteria, which in the larvae are housed in the cells of their own organ ( mycetoma ), which is located anteriorly at the junction of the foregut and midgut. If adult beetles are exposed to a temperature of 35 ° C for about 17 days, the bacteria die. The eggs of these symbiont-free beetles develop normally into finished beetles, the offspring of which die in the early larval stage, as the supply of the vital substances produced by the symbionts , which are not contained in the cereal grains or not contained in sufficient quantities, is exhausted. As far as we know, these substances are vitamins that have not yet been identified.

Synonyms

Several synonyms are known. Calandra granaria Fabricius, 1801, is common in German-language literature .

Damage infestation

Corn beetles attack different types of grain: rye, wheat, barley, spelled, milo, maize, oats, malt, rice, buckwheat, peeled acorns and pasta. If there are different types of grain to choose from, the beetles prefer rye. If stored goods are heavily infested, the temperature and humidity rise as a result of the activity of the beetles, which leads to severe consequential damage from mites and molds.

supporting documents

Individual evidence

  1. ↑ S. Büchner, G. Wolf: The grain beetle -  Sitophilus granarius (Linné) - from a band ceramic pit near Göttingen. In: Archaeological correspondence sheet. 27, No. 2, 1997, pp. 211-220.
  2. ↑ E. Schmidt: The grain beetle Sitophilus granarius Schoen. Curculionidae from the rubble layer of the ceramic band well in Erkelenz-Kückhoven. In: Brigitte Beyer (editor): Fountain of the Neolithic Age. International Symposium Erkelenz October 27-29, 1997. Rheinland-Verlag, Cologne 1998, ISBN 3-7927-1746-8 , pp. 261-269.
  3. ↑ a b c Hans Tielecke: The grain beetle. (= Die Neue Brehm-Bücherei. Volume 120). A. Ziemsen Verlag, Wittenberg Lutherstadt 1956, 32 pages.
  4. ↑ Hans Schneider: Artificially symbiont-free grain beetles ( Calandra granaria Lin.). Natural Sciences 41, 147/48 (1954).
  5. ↑ Hans Schneider: Morphological and experimental studies on the endosymbiosis of the grain and rice beetles ( Calandra granaria L. and Calandra oryzae ) L. Journal for Morphology and Ecology of Animals 44, 555-625 (1956).

literature

  • Hans Tielecke: The grain beetle. (= Die Neue Brehm-Bücherei. Volume 120). A. Ziemsen Verlag, Wittenberg Lutherstadt 1956, 32 pages.
  • Karl Wilhelm Harde, Frantisek Severa and Edwin Möhn: The Kosmos Käferführer: The Central European Beetles. Franckh-Kosmos Verlags-GmbH & Co KG, Stuttgart 2000, ISBN 3-440-06959-1 .
  • Jiři Zahradnik, Irmgard Jung, Dieter Jung et al .: Käfer Central and Northwestern Europe , Parey Berlin 1985, ISBN 3-490-27118-1 .
  • Rudy Plarre: An attempt to reconstruct the natural and cultural history of the granary weevil, Sitophilus granarius (Coleoptera: Curculionidae). European Journal of Entomology 107/1, 2010, 1–11 ( [1] ; PDF file; 134 kB).
  • Hans Schneider: Artificially symbiont-free grain beetles ( Calandra granaria Lin.). Natural Sciences 41, 147/48 (1954).
  • Hans Schneider: Morphological and experimental investigations on the endosymbiosis of grain and rice beetles ( Calandra granaria L. and Calandra oryzae ) L. Journal for Morphology and Ecology of Animals 44, 555-625 (1956).
  • Gary A. King, Harry Kenward, Edith Schmidt, David Smith: Six-Legged Hitchhikers: An Archaeobiogeographical Account of the Early Dispersal of Grain Beetles , in: Journal of the North Atlantic 23 (2014) 1-18.

Web links

Commons : Kornkäfer ( Sitophilus granarius )  - Album with pictures, videos and audio files