Adephaga

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Adephaga Temporal range: Changhsingian/Induan–Holocene, 251.2–0 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N
Dytiscus latissimus, a predaceous diving beetle
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Suborder:	Adephaga Schellenberg, 1806
Families
Extant families: Amphizoidae Aspidytidae Carabidae Dytiscidae Gyrinidae Haliplidae Hygrobiidae Meruidae Noteridae Rhysodidae Trachypachidae Extinct families: Colymbothetidae Coptoclavidae Liadytidae Parahygrobiidae

The Adephaga (from Greek ἀδηφάγος, adephagos, "gluttonous"), with more than 40,000 recorded species in 10 families, are a suborder of highly specialized beetles and the second-largest suborder of the order Coleoptera. Members of this suborder are collectively known as adephagans. By far the largest group comprising most of the suborder are the Carabidae (ground beetles, including tiger beetles), with over 40,000 species. Adephaga also includes a variety of aquatic beetles, such as predaceous diving beetles and whirligig beetles.

Anatomy[]

Adephagans have simple antennae with no or clubs. The galeae of the maxillae usually consist of two segments. Adult adephagans have visible notopleural sutures. The first visible abdominal sternum is completely separated by the hind coxae, which is one of the most easily recognizable traits of adephagans. Five segments are on each foot.

Wings[]

The of the hind wing is near the wing tip. The ends at this fold, where it is joined by a .

Internal organs[]

Adephagans have four Malpighian tubules. Unlike in other beetles, alternate with in the of adephagans. The coiled, tubular testes consist of a single follicle, and the ovaries are polytrophic.

Chemical glands[]

All families of adephagan have paired pygidial glands located posterodorsally in the abdomen, which are used for secreting chemicals. The glands consist of complex invaginations of the cuticle lined with epidermal cells contiguous with the integument. The glands have no connection with the rectum and open on the eighth abdominal tergum.

Secretions pass from the , which are aggregations of secretory cells, through a tube to a reservoir lined with muscles. This reservoir then narrows to a tube leading to an opening valve. The secretory lobes differ structurally from one taxon to another; it may be elongated or oval, branched basally or apically, or unbranched.

Delivery of glandular compounds[]

The secretion is realized in one of these manners:

• Oozing: if the gland is not muscle-lined, the discharge is limited in amount.
• Spraying: if the gland is muscle-lined, which is typically the case of carabids, the substances are ejected more or less forcefully.
• Crepitation is only associated with the Brachininae carabids and several related species. See bombardier beetle for a detailed description of the mechanism.

The secretions differ in the chemical constituents, according to the taxa. Gyrinids, for instance, secrete such as , , , or . Dytiscids discharge aromatic aldehydes, esters, and acids, especially benzoic acid. Carabids typically produce carboxylic acids, particularly formic acid, methacrylic acid, and tiglic acid, but also , , phenols, aromatic aldehydes, and quinones. Accessory glands or modified structures are present in some taxa: the Dytiscidae and Hygrobiidae also possess paired prothoracic glands secreting steroids; and the Gyrinidae are unique in the extended shape of the external opening of the pygidial gland.

The function of many compounds remain unknown, yet several hypotheses have been advanced:

• As toxins or deterrent against predators, some compounds indirectly play this role by easing the penetration of the deterrent into the predator's integument.
• Antimicrobial and antifungal agents (especially in )
• A means to increase wetability of the integument (especially in Hydradephaga)
• Alarm pheromones (especially in Gyrinidae)
• Propellant on water surfaces (especially in Gyrinidae)
• Conditioning plant tissues associated with oviposition

Distribution and habitat[]

Habitats range from caves to rainforest canopy and alpine habitats. The body forms of some are structurally modified for adaptation to habitats: members of the family Gyrinidae live at the air-water interface, rhysodines live in heartwood, and paussine carabids inhabit ant nests.

Feeding[]

Most species are predators. Other less-typical forms of feeding include: eating algae (family Haliplidae), seed-feeding (arpaline carabids), fungus-feeding (rhysodine carabids), and snail-feeding (licinine and carabids). Some species are ectoparasitoids of insects (brachinine and lebiine carabids) or of millipedes ( carabids).

Reproduction and larval stage[]

Some species are ovoviviparous, such as pseudomorphine carabids.

The larvae are active, with well-chitinized cuticle, often with elongated cerci and five-segmented legs, the foot-segment carrying two claws. Larvae have a fused labrum and no .

Phylogeny[]

Adephagans diverged from their sister group in the Late Permian, the most recent common ancestor of living adephagans probably existing in the early Triassic, around 240 million years ago. Both aquatic and terrestrial representatives of the suborder appear in fossil records of the late Triassic. The Jurassic fauna consisted of , carabids, gyrinids, and haliplid-like forms. The familial and tribal diversification of the group spans the Mesozoic, with a few tribes radiating explosively during the Tertiary.

The phylogeny of adephagans is disputed. The group is usually divided into two main groups:

• The comprise the two terrestrial families Carabidae and Trachypachidae (the Trachypachidae are sometimes considered a subfamily of the Carabidae).
• The , gathering all other families, are aquatic.

This division is often criticized, as mounting evidence is pointing out that the two groups are not monophyletic.

See also[]

• List of subgroups of the order Coleoptera

References[]

• ZoolScripta37:647
• "Adephaga". Integrated Taxonomic Information System.
• Adephaga Tree of Life