The Adephaga (from Greek language ἀδηφάγος, adephagos, "gluttonous") are a suborder of beetles, and with more than 40,000 recorded species in 10 families, the second-largest of the four beetle suborders. Members of this suborder are collectively known as adephagans. The largest family is Ground beetle (ground beetles) which comprises most of the suborder with over 40,000 species. Adephaga also includes a variety of aquatic beetles, such as predaceous diving beetles and .
Anatomy
Adephagans have simple antennae with no
pectination or clubs. The of the maxillae usually consist of two segments. Adult adephagans have visible
notopleuron sutures. The first visible
abdomen sternum is completely separated by the hind
Arthropod leg, which is one of the most easily recognizable traits of adephagans. Five segments are on each foot.
Wings
The
transverse fold of the
insect wing is near the wing tip. The
median nervure ends at this fold, where it is joined by a
cross nervure.
Internal organs
Adephagans have four Malpighian tubules. Unlike the genetical structures of other beetles, yolk chambers alternate with egg chambers in the ovarian tubes of adephagans. The coiled, tubular
testes consist of a single follicle, and the
ovary are
polytrophic.
Chemical glands
All families of adephagan have paired
pygidium located posterodorsally in the
abdomen, which are used for secreting chemicals. The glands consist of complex
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
Secretion can occur in multiple 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: boiling noxious chemical spray ejected with a popping sound. Crepitation is only associated with the Brachininae carabids and several related species. See bombardier beetle for a detailed description.
The secretions differ in the chemical constituents, according to the taxa. Gyrinidae, for instance, secrete Sesquiterpene such as gyrinidal, gyrinidione, or gyrinidone. Dytiscidae discharge aromatic , , and , especially benzoic acid. Carabidae typically produce , particularly formic acid, methacrylic acid, and tiglic acid, but also , , , aromatic aldehydes, and .
Accessory glands or modified structures are present in some taxa: the Dytiscidae and Hygrobiidae also possess paired prothorax glands secreting ; 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 or deterrent against ; some compounds indirectly play this role by easing the penetration of the deterrent into the predator's integument.
-
Antimicrobial and Fungicide agents (especially in Hydradephaga)
-
A means to increase Wetting of the integument (especially in Hydradephaga)
-
Alarm (especially in Gyrinidae)
-
Propellant on water surfaces (especially in Gyrinidae)
-
Conditioning plant tissues associated with oviposition
Distribution and habitat
Habitats range from
to
rainforest canopy and
alpine climate habitats. The body forms of some are structurally modified for adaptation to habitats: members of the family Gyrinidae live at the
Neuston,
Rhysodinae live in
heartwood, and
Paussinae carabids inhabit
.
Feeding
Most species are
. Other less-typical forms of feeding include:
algophagy (family
Haliplidae), seed-feeding (
Harpalinae carabids),
mycophagy (rhysodine carabids), and
snail (
Licininae and
Cychrini carabids). Some species are
of insects (
Brachininae and
Lebiinae carabids) or of
(
Peleciinae carabids).
Reproduction and larval stage
Some species are
ovoviviparous, such as
Pseudomorphinae carabids.
The are active, with well- cuticle, often with elongated cercus 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
Lopingian, 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 period.
The adephagans were formerly grouped into the Geadephaga with the two terrestrial families Carabidae and Trachypachidae and the Hydradephaga, for the aquatic families. However this is no longer used as the Hydradephaga are not a monophyletic group. Modern analysis has supported the clade Dytiscoidea instead, which includes many aquatic adephagans, notably excluding Gyrinidae.
Cladogram of the relationships of living adephagan families after Vasilikopoulos et al. 2021[
]
See also
-
List of subgroups of the order Coleoptera
