Darkling beetle

Darkling beetle
Alphitobius sp. (Tenebrioninae: Alphitobiini) Scale bar (top right) is 2 mm
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Suborder:	Polyphaga
Superfamily:	Tenebrionoidea
Family:	Tenebrionidae Latreille, 1802

Darkling beetle is the common name of the large family of beetles, Tenebrionidae. The number of species in the Tenebrionidae is estimated at more than 20,000 and the family is cosmopolitan. Human transport has spread several individual species inadvertently so that each of them has become cosmopolitan. Examples include Tribolium castaneum and other now-cosmopolitan pests of stored products.

Taxonomy and naming

The name Tenebrionidae means roughly: "those that are like Tenebrio"; Tenebrio was the Latin generic name that Linnaeus had assigned to some flour beetles in his 10th edition of Systema Naturae 1758-59. Tenebrio in turn literally means "seeker of dark places" or figuratively a trickster. In English, "darkling" is a more or less literal translation of tenebrio, meaning "dweller in dark".

Many species do inhabit dark places, but there are exceptions; for example, many species of Tenebrionidae in genera such as Stenocara and Onymacris are active by day and inactive at night. The name Tenebrionidae accordingly reflects the knowledge available to the taxonomists who first assigned the name; it is not a general reflection of tenebrionid biology.

The family Tenebrionidae not only includes a large number of species, but also an immensely varied range of forms, so much so that it presents great difficulties in classification. Taxonomic work still is in progress, but the following list of subfamilies was largely accepted in 2005.

• Alleculinae Laporte, 1840
• Cossyphodinae Wasmann, 1899
• Diaperinae Latreille, 1802
• Lagriinae Latreille, 1825 (1820)
• Nilioninae Lacordaire, 1859
• Phrenapatinae Solier, 1834
• Pimeliinae Latreille, 1802
• Stenochiinae Kirby, 1837
• Tenebrioninae Latreille, 1802
• Zolodininae Watt, 1974

The misspelling "T e r e b r i o n i d a e", though unusual, occurs frequently enough to be a nuisance and, because it is easily overlooked, it is a possible source of confusion in scans of the literature. The error appears to have no particular significance, but to be the product of misreadings, mis-scans, and mis-typings.

Characteristics

The Tenebrionidae may be identified by a combination of features, including :

• Their 11-segmented antennae that may be filiform, moniliform, or weakly clubbed
• First abdominal sternite is entire and not divided by the hind coxae
• Eyes are notched by a frontal ridge
• The tarsi have four segments in the hind pair and five in the fore and mid legs (5-5-4), tarsal claws are simple

Biology and ecology

Tenebrionid beetles occupy ecological niches in mainly deserts and forests as plant scavengers. Most species are generalistic omnivores, and feed on decaying leaves, rotting wood, fresh plant matter, dead insects, and fungi as larvae and adults. However, several genera, including Bolitotherus, are specialized fungivores which feed on polypores. Many of the larger species are flightless, and those which are capable, such as Tenebrio molitor, only do so when necessary, such as when dispersing or malnourished.

The larvae, known as mealworms or false wireworms, are usually fossorial, heavily armored, and nocturnal, and may possibly be an important resource for certain invertebrates and small mammals. However, the adults of many species have chemical defenses and are relatively protected against predators. Adults of most species, except grain pests, have slow metabolisms, and live extremely long compared to other insects, from approximately six months to two years.

Some species live in intensely dry deserts such as the Namib, and have evolved adaptions by which they collect droplets of fog that deposit on their elytra. As the droplets accumulate the water drains down the beetles' backs to their mouthparts, where they swallow it.

Notable species

The larval stages of several species are cultured as feeder insects for captive insectivores or as laboratory subjects:

• Tenebrio molitor is commonly used to feed terrestrial amniotes kept in terraria.
• Tribolium castaneum is a laboratory animal useful as a model organism, especially in studies of intragenomic conflict and population ecology.
• Zophobas morio, or superworm, is valued as a feed for captive reptiles; it contains less chitin than Tenebrio molitor.
• Alphitobius diaperinus or lesser mealworm larvae are smaller than Tenebrio molitor and thus more suitable as feed for smaller reptiles.

• Many tenebrionids are pests of cereal and flour silos and other storage facilities, including T. castaneum, other Tribolium species such as Tribolium confusum and Tribolium destructor, and Gnathocerus cornutus.

• In southwestern North America, species of the genus Eleodes (particularly E. obscurus) are well known as "pinacate beetles" or "desert stink beetles".

• Several genera, such as Stenocara and Onymacris, are of interest in ecological studies of arid conditions and their associated adaptations.

• Palembus dermestoides or Ulomoides dermestoides, known as "peanut beetle", "cancer beetle", or "asthma beetle", is eaten in Argentina where it is thought to be a treatment for cancer, asthma, and other illnesses.

Image gallery

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  Diaperis boleti under bark of oak.

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  Lagria sp. (Lagriinae) in Tanzania

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  A Platynotina species (Tenebrioninae) in India

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  Stenocara dentata in southern Africa

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  Gonopus tibialis

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  Pie dish beetle, Helea sp. in Australia

External links

• Tenebrionidae.net- information and pictures about darkling beetles
• Alphitobius diaperinus, lesser mealworm. University of Florida IFAS
• Leichenum canaliculatum variegatum, Madagascar beetle University of Florida IFAS