The Adephaga (from
Greek ἀδηφάγος, ''adephagos'', "gluttonous") are a suborder of
beetles
Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describe ...
, 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
Carabidae (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
whirligig beetles.
Anatomy
Adephagans have simple
antennae with no
pectination or clubs. The
galeae of the
maxillae usually consist of two segments. Adult adephagans have visible
notopleural sutures. The first visible
abdominal
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
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
transverse fold of the
hind 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
A testicle or testis (plural testes) is the male reproductive gland or gonad in all bilaterians, including humans. It is homologous to the female ovary. The functions of the testes are to produce both sperm and androgens, primarily testoste ...
consist of a single follicle, and the
ovaries
The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...
are
polytrophic.
Chemical glands
All families of adephagan have paired
pygidial gland
In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland).
Structure
De ...
s located posterodorsally in the
abdomen
The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the to ...
, which are used for secreting chemicals. The glands consist of complex
invaginations of the
cuticle
A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
lined with
epidermal cells contiguous with the
integument. The glands have no connection with the
rectum
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon) at the l ...
and open on the eighth abdominal
tergum
A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or ' ...
.
Secretions pass from the
secretory lobes, 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
Bombardier beetles are ground beetles (Carabidae) in the tribes Brachinini, Paussini, Ozaenini, or Metriini—more than 500 species altogether—which are most notable for the defense mechanism that gives them their name: when disturbed, they e ...
for a detailed description.
The secretions differ in the chemical constituents, according to the taxa.
Gyrinids, for instance, secrete
norsesquiterpenes such as gyrinidal, gyrinidione, or gyrinidone.
Dytiscids discharge aromatic
aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl gro ...
s,
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...
s, and
acid
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a se ...
s, especially
benzoic acid
Benzoic acid is a white (or colorless) solid organic compound with the formula , whose structure consists of a benzene ring () with a carboxyl () substituent. It is the simplest aromatic carboxylic acid. The name is derived from gum benzoin ...
.
Carabids typically produce
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...
s, particularly
formic acid
Formic acid (), systematically named methanoic acid, is the simplest carboxylic acid, and has the chemical formula HCOOH and structure . It is an important intermediate in chemical synthesis and occurs naturally, most notably in some ants. Est ...
,
methacrylic acid, and
tiglic acid, but also
aliphatic ketones,
saturated esters,
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it r ...
s, aromatic aldehydes, and
quinone
The quinones are a class of organic compounds that are formally "derived from aromatic compounds uch as benzene or naphthalene">benzene.html" ;"title="uch as benzene">uch as benzene or naphthalene] by conversion of an even number of –CH= group ...
s.
Glossary of entomology terms, Accessory glands or modified structures are present in some taxa: the
Dytiscidae and
Hygrobiidae also possess paired
prothoracic glands secreting
steroid
A steroid is a biologically active organic compound with four rings arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and ...
s; 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
toxin
A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...
s or deterrent against
predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
s; some compounds indirectly play this role by easing the penetration of the deterrent into the predator's
integument.
*
Antimicrobial and
antifungal
An antifungal medication, also known as an antimycotic medication, is a pharmaceutical fungicide or fungistatic used to treat and prevent mycosis such as athlete's foot, ringworm, candidiasis (thrush), serious systemic infections such as ...
agents (especially in
Hydradephaga)
*A means to increase
wettability 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
Habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s range from
cave
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
s to
rainforest
Rainforests are characterized by a closed and continuous tree canopy, moisture-dependent vegetation, the presence of epiphytes and lianas and the absence of wildfire. Rainforest can be classified as tropical rainforest or temperate rainfores ...
canopy and
alpine
Alpine may refer to any mountainous region. It may also refer to:
Places Europe
* Alps, a European mountain range
** Alpine states, which overlap with the European range
Australia
* Alpine, New South Wales, a Northern Village
* Alpine National P ...
habitats. The body forms of some are structurally modified for adaptation to habitats: members of the family Gyrinidae live at the
air-water interface,
Rhysodinae live in
heartwood, and
Paussinae carabids inhabit
ant nests.
Feeding
Most species are
predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
s. Other less-typical forms of feeding include:
eating algae (family
Haliplidae), seed-feeding (
harpaline carabids),
fungus-feeding (rhysodine carabids), and
snail-feeding (
licinine and
cychrine carabids). Some species are
ectoparasitoids of insects (
brachinine and
lebiine carabids) or of
millipedes (
peleciine carabids).
Reproduction and larval stage
Some species are
ovoviviparous, such as
pseudomorphine carabids.
The
larva
A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.
...
e are active, with well-
chitin
Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...
ized cuticle, often with elongated
cerci and five-segmented legs, the foot-segment carrying two claws. Larvae have a fused
labrum and no
mandibular molae.
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
The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
, 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
trachypachids, carabids, gyrinids, and
haliplid-like forms. The familial and tribal diversification of the group spans the
Mesozoic
The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
, with a few tribes radiating explosively during the
Tertiary
Tertiary ( ) is a widely used but obsolete term for the geologic period from 66 million to 2.6 million years ago.
The period began with the demise of the non-avian dinosaurs in the Cretaceous–Paleogene extinction event, at the start ...
.
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.
Rhysodidae is suggested to represent a subgroup of Carabidae rather than a distinct family, with
Cicindelidae often being treated as a distinct family from Carabidae.
Cladogram of the relationships of living adephagan families after Vasilikopoulos et al. 2021
and Baca et al. 2021:
See also
*
List of subgroups of the order Coleoptera
References
*
*
AdephagaTree of Life
{{DEFAULTSORT:Adephaga
Insect suborders