bean weevil

bean weevil

bean weevil, common name for a well-known cosmopolitan species of beetle (Acanthoscelides obtectus) that attacks beans and is thought to be native to the United States. It belongs to the family Bruchidae, the seed beetles. The bean weevil is small, about 1/6 in. (0.4 cm) long, and stout-bodied, with a short broad snout and shortened wing covers (elytra). The adults attack legumes either in storage or in the field and may even completely destroy them. The grubs, or larvae, hatch from eggs laid in holes that have been chewed by the female into stored beans or into pods in the field. In heavy infestations there may be two dozen or more newly hatched larvae in one bean. When full-grown, the larvae form pupae in the eaten-out cavity. As many as six generations are produced in a single season, and in storage breeding continues as long as there is available food left in the beans and a warm temperature. The larvae can be killed by fumigation or by heating the seeds to 145°F; (63°C;) for two hours. Bean weevils are classified in the phylum Arthropoda, class Insecta, order Coleoptera, family Bruchidae.

The bean weevils or seed beetles are a subfamily (Bruchinae) of beetles, now placed in the family Chrysomelidae, though they have historically been treated as a separate family. They are granivores, and typically infest various kinds of seeds or beans, living for most of their lives inside a single seed. The family includes about 1,350 species found worldwide.

Bean weevils are generally compact and oval in shape, with small heads somewhat bent under. Sizes range to 1 mm, up to 22 mm for some tropical species. Colors are usually black or brown, often with mottled patterns. Although their mandibles may be elongate, they do not have the long snouts characteristic of true weevils.

Adults deposit eggs on seeds, then the larvae chew their way into the seed. When ready to pupate, the larvae typically cut an exit hole, then return to their feeding chamber. Adult weevils have a habit of feigning death and dropping from a plant when disturbed.

Host plants tend to be legumes, but species will also be found in Convolvulaceae, Arecaceae, and Malvaceae, and several species are considered pests.

One characteristic of the beetles which can be seen in the photo is that the elytra are short, not quite reaching the tip of the abdomen.

The adult beetles are occasionally found in the United Kingdom when they emerge out of stored products in warehouses & dwellings, but they cannot proliferate in unheated buildings in that climate.

Notable species


This list of genera follows the old systematics, when the family Bruchidae was still valid.

* Rhaebus Fischer von Waldheim, 1824

* Pachymerini Bridwell, 1929
* Pachymerus Thunberg, 1805
* Butiobruchus Prevett, 1966
* Caryobruchus Bridwell, 1929
* Caryoborus Schoenherr, 1833
* Caryedonini Bridwell, 1929
* Mimocaryedon Decelle, 1968
* Caryedon Schoenherr, 1823
* Caryotrypes Decelle, 1968
* Aforedon Decelle, 1965
* Exoctenophorus Decelle, 1968
* Caryopemonini Bridwell, 1929
* Protocaryopemon Borowiec, 1987
* Diedobruchus Pic, 1913
* Caryopemon Jekel, 1855

* Amblycerini Bridwell, 1932
* Amblycerus Thunberg, 1815
* Spermophagini Borowiec, 1987
* Zabrotes Horn, 1885
* Spermophagus Schoenherr, 1833

* Eubaptus Lacordaire, 1945

* Kytorhinus Fischer von Waldheim, 1809

* Bruchini Latreille, 1802
* Bruchus Linnaeus, 1767
* Megacerini Bridwell, 1946
* Megacerus Fahraeus, 1839
* Acanthoscelidini Bridwell, 1946
* Gibbobruchus Pic, 1913
* Ctenocolum Kingsolver & Whitehead, 1974
* Caryedes Hummel, 1827
* Meibomeus Bridwell, 1946
* Penthobruchus Kingsolver, 1973
* Pygiopachymerus Pic, 1911
* Merobruchus Bridwell, 1946
* Acanthoscelides Schilsky, 1905
* Mimosestes Bridwell, 1946
* Stylantheus Bridwell, 1946
* Altheus Bridwell, 1946
* Pseudopachymerina Zacher, 1952
* Neltumius Bridwell, 1946
* Stator Bridwell, 1946
* Sennius Bridwell, 1946
* Megasennius Whitehead & Kingsolver, 1975
* Algarobius Bridwell, 1946
* Scutobruchus Kingsolver, 1968
* Rhipibruchus Bridwell, 1932
* Pectinibruchus Kingsolver, 1967
* Dahlibruchus Bridwell, 1931
* Cosmobruchus Bridwell,, 1931
* Lithraeus Bridwell, 1952
* Bonaerius Bridwell, 1952
* Spatulobruchus Borowiec, 1987
* Palpibruchus Borowiec, 1987
* Specularius Bridwell, 1938
* Acanthobruchidius Borowiec, 1980
* Palaeoacanthoscelides Borowiec, 1985
* Horridobruchus Borowiec, 1984
* Callasobruchus Pic, 1902
* Bruchidius Schilsky, 1905
* Salviabruchus Decelle, 1982
* Sulcobruchus Chujo, 1937
* Parasulcobruchus Anton, 1999
* Borowiecus Anton, 1994
* Megabruchidius Borowiec, 1984
* Conicobruchus Decelle, 1951
* Kingsolverius Borowiec, 1987
* Decellebruchus Borowiec, 1987
* Margaritabruchus Romero & Johnson, 2001


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