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Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Dytiscidae
Genus:	Rhantus
Species:	R. suturalis
Binomial name
Rhantus suturalis (Munchin, 2010)

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Rhantus suturalis is a diving beetle found all around New Zealand

Introductory

Rhantus suturalis, is a beetle in the family of predaceous diving beetles from the Subfamily of Colymbetinae. The beetle is found all around New Zealand in still water habitats

Description

The diving beetle has a light yellow colored margin which acts as a golden base that suggests the elytra are dark brown when seen from a normal distance but with close proximity the colour is dense black. It has a rhombus-shaped dot on the neck shield . It typically grows to about 5.7- 17.8mm (about 0.2 in) long. The visual system of the Rhantus suturalis’s is stemmata and it is strongly related to flight type . The beetle has a narrow metasternal wings which enable it to fly long distance

Distribution

The Diving beetle is among the most widely disseminated water beetles in the world; it is originated from New Guinea and has since scatter south to Australia and New Zealand. It has spread north to Europe, southern Palaearctic region, including Mediterranean North Africa, stretching from Asia Minor to China. It is also found in remote islands like Hawaii, the Galápagos and Tristan da Cunha. Moreover, in New Zealand, the diving beetle has spread through both the North Island and South Island. However, the majority of its population settles in the North Island (Ref 2)because it is warmer than the South Island where their preferred water temperature ranged between 10 and 21 Celsius degrees occurs

Diving beetles mostly settle in slow flowing streams, weedy bonds, streams and pools. They favor pond-like habitats over any other water habitat because it has medium to low tolerance value, meaning that they are tolerant taxa. Furthermore, other beetles prefer seasonal pools like vernal pools and some temporary habitats. Rhantus suturalis is also found at extreme elevations. One of the most important environmental elements driving beetle species variety in river ecosystems is vegetation

Life Cycle

The beetles exhibit different mating behaviors. For instance, females release sex pheromones that are used by males to locate mating partners; the use of stridulatory devices by males indicates sexual signaling. Furthermore, in some cases sexual antagonism is present between female and male.

Females of R. suturalis release pheromones that appear to fit the description of aggregation pheromones. The female attraction is similar to the male sex pheromone communication systems found in many phytophagous insects. Males release pheromones, which are likely to attract females, and conspecific males. Conspecific males are attracted because they eavesdrop on the pheromones to gain mating without releasing pheromones themselves . This is called aggregation pheromones.

Mate finding in the Rhantus genus (Colymbetinae), based on the fact that males and females can find each other in complete darkness.

The diving beetle males are able to hold the females underwater while mating, reducing access to air which indicates a coercive male strategy. They use their large sucker-shaped adhesive setae ventrally to stop diving beetles females from resisting.

Life cycle of the Rhantus suturalis has five stages till adulthood. Most of the life stages of the diving beetle most takes place in the water. Eggs are laid underwater near the “splash zone”, where they are placed on aquatic leaves. Rhantus females at this strategy, drops eggs randomly on a substrate because they have a short and bear numerous tactile setae . Compare to other genus females such as Aciliini, have long ovipositors enabling them to carefully hide their eggs behind aquatic leaves from predators.

Furthermore, the timing of oviposition to hatching depends on the time of the year the egg was laid, the temperature of the water. Some of the species' hatch within 5-14 days and some eggs hatch during the winter season.

The diving beetle has three larval instars (instar I, instar II, instar III) and all those known stayed in the water as only the pupal stages leave the water pupate.The development process of the larvae depends on the environment where the species is settled. External factors such as temperature contribute to larval development. However, other factors affecting larval development are unknown. Moreover, to distinguish between the three larval instars, Instar I show the development of spinous egg-bursters on the posterior portion of the fronto- clypeus. This is the development of the frontal plate of the beetle. Most weight and size are gain in Instar II. Instar III is when functional spiracles on abdominal segments are present, these are use to when they leave the water to pupate in areas of soil or moss.

The pupae stage and pupation of the Rhantus suturalis is not well studied. Furthermore, the pupation cell is made from when the larvae move in the soil or in some cases the larval mandibles are used for construction of a chamber. This cell is find near water and often develops near stones or boards.

Moreover, the life cycle of Rhantus suturalis is multivoltine. Multivoltine means that the beetle can brood two or more offspring per year. Herewith, their life cycle strategies works in different types of seasonality especially settling in New Zealand. Thus, in seasonal dry areas may cause both the egg and adult stage to go through a terrestrial diapause until the aquatic habitat becomes available again. This causes the species to migrate to other sites. For instance, when a pond dry up the beetle will be forced to leave in search for other wet habitats. This occurs until it rains or the cause vernal melting by season changes, summer, will provide greater number bodies of water.

Interactions

The diving beetle has larvae that are fluid- feeding predators and adults that are active swimmers feeding on other pond invertebrates. Moreover, Rhantus suturalis larval stage prey upon aquatic invertebrates but their short sickle-shaped mandible makes it difficult for them to loot and swallow solid food like their prey when capture.

Prey detection includes visual scanning, tactile and chemical cues. However, high plant density in water or streams may act as an interruption to when the beetle is hunting.

Rhantus suturalis adults are carnivorous but also feed occasionally on plants. If confined, adult diving beetles can lay their eggs on animal tissues without plant component.

Furthermore, larvae and adults are targeted by aquatic species such as Anguilla australis (short-finned eel) otter plus, preyed on by birds and other fish species. They also have a rich variety of microfauna in the gut and are parasitized by Lathromeroidea silvarum .

Further Information

The R. suturalis-group is most diverse throughout the Palaearctic compared to other genus.

The diving beetle is used as indicators of toxicity, pollution, water and wetland quality. They are useful indicators of biodiversity; together with other aquatic beetle families they can indicate areas that are important to conserve. They play a role as predatory pests in fish farming and good in controlling medically important taxa such as mosquitoes.

Furthermore, adult diving beetles play a big role in other cultures. They are used as traditional food in Eastern and South-Eastern Asia, and some are farmed for consumption.They are also found in creation stories of other culture.