Rice beetle
| Rice beetle | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Rice beetle ( Sitophilus oryzae ) |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Sitophilus oryzae | ||||||||||||
| ( Linnaeus , 1763) |
The rice weevil or rice granary weevil ( Sitophilus oryzae ) is a beetle from the subfamily of dryophthorinae the weevil .
The species is a stored product pest and can cause significant damage to food stores.
features
The beetle is elongated, cylindrical, brownish-red in color, with a light reddish spot on each wing-cover: behind the shoulder and in front of the tip. They are about two to three millimeters long. The elytra are roughly striped with strong, roughly dotted stripes and narrow spaces in which a row of short, upright hair bristles sit. You leave the last abdomen sterngite uncovered as pygidium , but this is not visible when looking at it (because it slopes vertically). The roughly dotted pronotum is longer than it is wide and of the same width as the elytra. The head has a round, cylindrical trunk that is stretched forward. The antennae are turned in near the base of the trunk, the trunk is somewhat thickened at this point. The splints of all pairs of legs have a strong, inwardly curved mandrel at the end.
The species is difficult to distinguish from the closely related corn beetle Sitophilus zeamais . The rice grain beetle is slightly smaller and lighter in color, the pronotum is duller thanks to shagreen coating (a surface pattern of fine longitudinal cracks that form cells). In the male, the aedeagus does not have a fine longitudinal groove on the upper side as in the zeamais . Individual individuals cannot always be reliably distinguished morphologically, but the independence of the species has been proven by means of DNA analyzes.
It is essential to note: A reliable determination is not possible on the basis of the infected grains. Although the individual Sitophilus species have preferences for specific grains, they may be found in a large number of cereal grains.
Way of life
Rice grain beetles live outdoors in the tropics and attack grains in the fields. In Central Europe, however, they can only survive in heated buildings. They occur in warehouses and supplies of all kinds and can also be dragged around the household.
The females lay 100 to 200 eggs individually on cereal grains . B. corn and wheat can also be attacked. The animals prefer moderate to high temperatures for reproduction. From approx. 15 ° C an increase is possible. The preferred temperature is around 27 ° C. The beetles are quite drought-resistant, but prefer moist conditions and reproduce faster here. Development is no longer possible below 35% relative humidity.
To lay their eggs, the beetles drill a hole in a grain of corn with their mouthparts and lay one egg in each. Then the hole is closed again with a secretion. After being deposited, the egg develops into a larva in the grain. This pupates and after a total of 20 to 100 days, depending on the ambient temperature, the finished beetle frees itself from the hollowed out grain. A fully grown beetle can survive for months without eating.
Combat
While the control in the household is quite unproblematic (dispose of infected supplies), the control of the species in camps and industrial plants is a serious problem. The usual control with insecticides (especially malathion ) often fails due to the development of resistance of the species. Alternatively, mechanical and biological methods are used tested. Polished rice (with the pericarp peeled off ) is less affected than whole grain. Reasons are, in addition to the unbalanced nutrient profile, that the closures of the larval cavity are often destroyed, making the larva more susceptible to predators. Essential biological antagonists parasitoid Hymenoptera , especially the types Anisopteromalus calandrae (Howard), Lariophagus distinguendus (Forster), Pteromalus cerealellae (Ashmead) and Theocolax elegans (Westwood) (all family Pteromalidae , jewel wasps ). In Japan, the infestation is quite successfully kept short by storage at temperatures below 10 ° C. Combating with carbon dioxide gas is possible, but this also leads to physiological adaptation (resistance).
Individual evidence
- ↑ Purnama Hidayat, Thomas W. Phillips, Richard H. French-Constant (1996): Molecular and Morphological Characters Discriminate Sitophilus oryzae and S. zeamais (Coleoptera: Curculionidae) and Confirm Reproductive Isolation. Annals of the Entomological Society of America, Volume 89, Number 5: 645-652.
- ↑ PW Likhayoa & RJ Hodges (2000): Field monitoring Sitophilus zeamais and Sitophilus oryzae (Coleoptera: Curculionidae) using refuge and flight traps baited with synthetic pheromones and cracked wheat. Journal of Stored Products Research 36: 341-353.
- ↑ DE Evans (1977): The capacity for increase at a low temperature of several Australian populations of Sitophilus oryzae (L.). Australian Journal of Ecology Volume 2, Issue 1: 55-67. doi : 10.1111 / j.1442-9993.1977.tb01127.x
- ^ BR Champ & CE Dyte (1977): FAO Global Survey of Pesticide Susceptibility of Stored Grain Pests. FAO Plant Protection Bulletin Vol. 25 No. 2: 49-67.
- ↑ Eric Lucas & Jordi Riudavets (2002): Biological and mechanical control of Sitophilus oryzae (Coleoptera: Curculionidae) in rice. Journal of Stored Products Research 38: 293-304.
- ↑ Hiroshi Nakakita & Hiroshi Ikenaga (1997): Action of low temperature on physiology of Sitophilus zeamais motschulsky and Sitophilus oryzae (L.) (Coleoptera: Curculionidae) in rice storage. Journal of Stored Products Research Volume 33, Issue 1: 31-38. doi : 10.1111 / j.1442-9993.1977.tb01127.x
- ↑ S. Navarro, R. Dias, E. Donahaye (1985): Induced tolerance of Sitophilus oryzae adults to carbon dioxide. Journal of Stored Products Research Volume 21, Issue 4: 207-213. doi : 10.1016 / 0022-474X (85) 90017-7
swell
GA, Lohse: 24th subfamily Rhynchophorinae. In: H. Freude, KW Harde, GA Lohse (editor): Die Käfer Mitteleuropas. Volume 11. Goecke and Evers Verlag, Krefeld 1983. ISBN 3 87263 031 8
Web links
- Sitophilus oryzae at Fauna Europaea