Acilius sulcatus
Introduction MaleThe male's front feet have suction cups'''''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.
Taxonomy ''A. sulcatus'' is known throughout Europe as the lesser diving beetle, a common name shared with many other aquatic beetles 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. A unique morph is, however, recognized in the Akfadou mountains of Algeria and has the potential to attain separate species status. Habitat loss due to logging and allopatric 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.
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 and vertebrate 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. ''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, 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. 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 predators, leading to narcosis. The steroids produced vary in levels of toxicity depending on food availability and photoperiod. ''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.
Gallery File:Acilius sulcatus.gemeiner furchenschwimmer.jpg| ''Acilius sulcatus'' femaleFile:Acilius sulcatus larvae.JPG|LarvaFile:Dytiscidae - Acilius sulcatus.JPG| ''Acilius sulcatus'', male and female; mounted specimenFile:Acilius sulcatus-fo.jpg|Female dorsal sideFile:Acilius sulcatus-fu.jpg|Female ventral side
Further reading Abjornsson, K., Wagner, B. M. A., Axelsson, A., Bjerselius, R. & Olse¨n, K. H. 1997 Responses of ''Acilius sulcatus'' (Coleoptera: Dytiscidae) to chemical cues from perch (''Perca fluviatilis''). ''Oecologia''. '''111''': 166–171.Bergstein, J. 2005.Taxonomy, phylogeny, and secondary sexual character evolution of diving beetles, focusing on the genus ''Acilius''. Umea University Print and Media. 6- 32Bergsten, J., K.B., Miller. 2005.Taxonomic revision of the Holarctic diving beetle genus ''Acilius'' Leach (Coleoptera: Dytiscidae). ''Systematic Entomology''. '''31''': 145–197.Cayrou J., and R. Cereghino. 2005.Life cycle phenology of some aquatic insects: implications for pond conservation. ''Aquatic Conservation: Marine and Freshwater Ecosystems''. '''15''': 559–571Chandra, G., S. K.,Mandel, Ghosh, A. K., Das, D., S. S., Banergee, Chakraborty, S .2008.Biocontrol of larval mosquitoes by ''Acilius sulcatus'' (Coleoptera: Dytiscidae). ''BMC Infectious Diseases''. '''8''': 138Fescemyer, H.W., and R.O., Mumma.1983.Regeneration and Biosynthesis of Dytisci Defensive Agents (Coleoptera: Dytiscidae). ''Journal of Chemical Ecology'' '''9(11)''': 1149–1464IUCN (International Union For Conservation Of Nature) (accessed 2012,09,05). http://www.iucn.org/ information on species distribution and ecological standingMarshal, J.N., and Diebel, C. (1995). 'Deep-Sea Spiders' That Walk through The Water. ''The Journal of Experimental Biology''. '''198''':1371–1379.Miller, J.R., R.O., Mumma. (1975). Physiological Activity Of Water Beetle Defensive Agents. I. Toxicity And Anesthetic Activity Of Steroids And Norsesquiterpenes Administered In Solution To The Minnow. ''Journal of Chemical Ecology'' '''2(2)'': 115- 130.Nilson, A.N., I., Ribera (1995). Morphometric Patterns Among Diving Beetles (Coleoptera: Noteridae, Hygrobiidae, and Dyscidae). ''Canadian Journal of Zoology''. '''73''': 2343- 2360.Swevers, J., J., Lambert, J.G.D., and de Loof (1991). Synthesis and Metabolism of Vertebrate-type Steroids by Tissues of Insects a Critical Evaluation. ''Experientia'' '''47''': 687–698
References * Fauna europaea* Biolib