''Acilius sulcatus'' is a species of water beetle in the family Dytiscidae. It is fairly large (14.4 – 18.2 mm), with color variation shown throughout its range. Typically it is yellow and black.

Range

''A. sulcatus'' has a worldwide distribution but is found primarily in

North Western Europe Northwestern Europe, or Northwest Europe, is a loosely defined subregion of Europe, overlapping Northern and Western Europe. The region can be defined both geographically and ethnographically. Geographic definitions Geographically, Northw ...

Taxonomy

''A. sulcatus'' is known throughout

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

as the lesser diving beetle, a common name shared with many other aquatic

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 describ ...

in the family Dytiscidae.

Habitat

Temporary and permanent water bodies. ''A. sulcatas'' shows a generalist response to habitat choice, living in bogs, ponds, streams, etc. As ''A. sulcatus'' is able to fly, it is not restricted to a single body of water. ''A. sulcatus'' is found in water bodies with high and low levels of vegetation, showing no preference between the two. They dominate in water bodies without any fish predators and are used as a primary indicator of predator presence.

Environmental pressures

''A. sulcatus'' is found over a large range and is not thought to face any pressures on the continuity of the species; as such, the beetle has not been evaluated by the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

. A unique morph is, however, recognized in the Akfadou mountains of

Algeria ) , image_map = Algeria (centered orthographic projection).svg , map_caption = , image_map2 = , capital = Algiers , coordinates = , largest_city = capital , relig ...

and has the potential to attain separate species status. Habitat loss due to logging and

allopatric Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

separation from other populations means that the morph deserves special attention. Due to its fairly large distribution, ''A. sulcatus'' population numbers have been used as an aid in the measurement of the ecological health of

wetlands A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...

Life cycle

''A. sulcatus'' is univoltine, with adults overwintering in deep permanent water bodies that neither dry out nor freeze completely. Mating pairs are found in both the spring and autumn. Females lay their eggs near water on the underside of plant matter. Eggs hatch after about one week. Larval development takes about 30 days, and pupal development takes another 16–28 days.

Feeding

''A. sulcatus'' is a predatory diving beetle which feeds upon small

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

and

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

prey. Larvae prefer micro-invertebrate prey, such as '' Daphnia'', whereas adults select size-appropriate prey. Known for its high aquatic speed, ''A. sulcatus'' actively pursues prey rather than using a sit-and wait ambush strategy seen in other

arthropods Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

. ''A. sulcatus'' is active both day and night. ''A. sulcatus'' larvae capture prey headfirst with their mandibles before injecting digestive enzymes for extra oral digestion. Adults do not use extra oral digestion, instead using their strong mouth parts to devour prey.

Morphology

Color varies throughout the range of ''A. sulcatus'' and is not a good identifying characteristic; however, ''A. sulcatus'' shows many unique structural morphologies useful for identification. ''A. sulcatus'' is easily recognized by its large, distinctive hind legs. The hind legs are long and fringed with

setae In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...

, forming a paddle-like shape when spread. The body is always wider than the height of the insect, and is streamlined (no spines or other chitinous structures protruding). As in all Dytiscidae beetles, the sternal keel is absent. ''A. sulcatus'' is clumsy on land, but it is well adapted for an aquatic lifestyle and is a strong flier. ''A. sulcatus'' may also be recognized by its unique reproductive structures. Males have three ventral suction disks used to secure the male to the slippery female during reproduction. Male attachment to females is detrimental to female survival as the mating period may attract predators. To avoid potential death in mating females show modifications of the elytra. The elytra is highly grooved with many suberect setae, making male attachment far more difficult. The male elytra is smooth without setae showing high levels of

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

. The competition between the sexes has led to an evolutionary sexual arms race.

Defensive strategy

Aquatic beetles in the family Dytiscidae possess defensive glands used to secrete agents repellent and toxic to vertebrate predators. Secretions primarily contain steroids synthesized from cholesterol. The steroids secreted act to

anesthetize ''Fear of a Blank Planet'' is the ninth studio album by British progressive rock band Porcupine Tree and their best selling before 2009's '' The Incident''. It was released on 16 April 2007 in the UK and the rest of Europe by Roadrunner, 24 A ...

predators, leading to narcosis. The steroids produced vary in levels of toxicity depending on food availability and

photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...

. ''A. sulcatus'' is highly adapted for aquatic movement and can make effective use of its speed to escape threats. When tested against 72 other common water beetle species, ''A. sulcatus'' was shown to have the highest movement velocity. During the day, ''A. sulcatus'' uses primarily visual information to avoid predators; however, in low-light conditions, chemical signals are used as the dominant cues for avoidance.). It has also been suggested that a 'humming' sound, produced by an interaction of the wings and the elytra, is used as a defensive strategy by causing an unpleasant vibrating sensation in the mouth of a predator.

Bio-control

Although it has not been put into practice, laboratory tests have shown ''A. sulcatus'' to be a highly effective predator of mosquito larvae. As such, its use as an environmentally friendly bio-control device is being examined.Chandra, G., et al. (2008)

Gallery

File:Acilius sulcatus.gemeiner furchenschwimmer.jpg, ''Acilius sulcatus'' female File:Acilius sulcatus larvae.JPG, Larva File:Dytiscidae - Acilius sulcatus.JPG, ''Acilius sulcatus'', male and female; mounted specimen File:Acilius sulcatus-fo.jpg, Female dorsal side File:Acilius sulcatus-fu.jpg, Female ventral side

References

Fauna europaeaBiolib
{{DEFAULTSORT:Acilius Sulcatus Dytiscidae Beetles of Europe Beetles described in 1758 Taxa named by Carl Linnaeus