Archichauliodes diversus

Archichauliodes diversus
Archichauliodes diversus (Walker, 1853), male specimen held at Auckland Museum licensed under CC BY 4.0
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Megaloptera
Family:	Corydalidae
Genus:	Archichauliodes
Species:	A. diversus
Binomial name
Archichauliodes diversus Walker, 1853

Archichauliodes diversus is an insect in the subfamily Corydalinae - the Dobsonflies. In its larval form It is commonly known by the name toe-biter, and its Maori name is puene. The species is native to New Zealand. Although there are other species of Dobsonfly in other parts of the world including Asia, Australia (Archichauliodes guttiferus) and South America, Archichauliodes diversus is the only species of Dobsonfly in New Zealand. The Dobsonfly larva is the largest species of freshwater insect found in fresh water and the only family representatives in New Zealand.

Description

Dobsonfly larvae are one of the biggest freshwater insects in New Zealand. The thorax and head are black and flattened, and the head has a large set of mandibles.^[1] The larvae are sturdy animals with heavily sclerotised heads and thoracic segments.^[2] The abdomen is long and light in colour and it has 8 pairs of tentacle-like gills projecting from abdominal segments 1-8. Like other dobsonfly larvae they have anal prolegs with a pair of terminal hooks which they use to attach themselves to substrate, and they lack a terminal filament (the end of the insects ovaries).^[3]

Distribution

Archichauliodes diversus is the only member of the genus found in New Zealand where it is endemic and common throughout the country.^[4] It is common in streams nationwide, with moderate to good water quality, and has tolerance values of 7 (hard bottom sites) and 7.3 (soft bottom sites).^[1]

A. diversus prefers stony or hard-bottom streams in bush covered and farmland areas ^[1][4] and also like to have overhanging canopy/bush overhead for shelter, lifestyle and large rock pools. It thrives in good quality water.^[5]

Life cycle/Phenology

Archichauliodes diversus larvae are aquatic and the adults are terrestrial. It spends most of its life in the aquatic juvenile stage (2–5 years).^[6][7] The larvae leaves the stream between every molt,^[2] a unique feature of this species. It has a generation time of more than a year,^[8] and the adult are found near streams.

The dobsonfly has many stages throughout its life. Changing greatly not only in size but also in appearance as it progresses from egg, larval, prepupal, pupal and imaginal stages. The dobsonfly is nocturnal, most active at dusk and at night. The first stage of the life cycle is the egg which is light yellow and cylindrical in appearance and shape when it is first laid. It then turns colour when open to air to a dark brown colour. This stage of the dobsonfly life lasts around 30 days. The larval stage is similar in appearance to the egg, but changes over time when newly emerged. They vary in size, but are roughly around 2.2mm and can grow to around 38.5mm when fully grown. When completely emerged, the larval appearance also changes from an egg to appear more like an insect. It has 8 pairs of ‘gills’ that run down the abdomen which acts as the respiration system. This is the only documented stage during which the dobsonfly eats. This stage occurs all year round. In the third stage the prepupa migrates towards the water edge or water banks. This phase occurs around the months of early July to late January and takes place for 15 weeks. This is due to the water levels being at maximum height as the prepupa needs the soils to be saturated for the next life cycle stage to occur. The pupal stage lasts around 20–24 days. This time frame also depends on the sex of the species, males take longer than females. This occurs around the months of late October to February. Although, the pupa is similar to the adults, it has a bigger build and immature wings. The colour changes in a matter of hours to days, the dobsonfly starts out pale in colour then changes to a dark brown. The last stage is the Imago stage. At this point the dobsonfly is a large insect. An adult dobsonfly only lives for roughly 6-10days. In this time, they spent most of their time resting in nearby trees. Before the Dobsonfly dies, the female lays several hundred eggs in irregular masses on nearby trees, scrubs, and rocks.^[9]

Diet

Archichauliodes diversus larvae are predatorial and use their large serrated mandibles to catch other aquatic invertebrates. This includes Mayfly,^[10] Aoteapsyche and Atalophlebioides.^[11] They are mostly active at night were they ambush prey around the center of riffles where there is a lot of oxygen and the turbulence stir up prey.^[12] The only stage that the Dobsonfly eats and preys is at the larvae stage and is therefore purely aquatic. At this point the larvae are often the most dominate in the waterways so have little small insect predators. Due to Dobsonfly larvae being nocturnal, they only feed at dusk and night. They are carnivores with the main food source being the mayfly naiades.^[13] They will also eat anything that comes in their way that they can hold with their ferocious jaws, this also includes eating their own species.^[5]

Predators, Parasites, and Diseases

Known species that prey on Archichauliodes diversus:^[1] include Brown trout, Galaxiidae and Galaxias

The biggest threat to dobsonflies is human intervention,^[14] by removing over hanging bush and trees from the waterways. This has a significant negative impact as it is a critical part in the life cycle of the Dobsonfly.^[10] The Dobsonfly is only found in good quality water. Any pollution could do serious damage to not only the Dobsonfly but also other species that could be potential food source. (Scarsbook et al. (2007). The larval stage is at risk of predation by Caddis fly larvae and Stonefly larvae. Spiders and beetles are also a risk for pupae and pre-pupal stages as arebirds and other spiders, such as Lycosid spiders.^[13]

Cultural uses

Dobsonflies are well known to naturalist and anglers because they are big, have a high endurance and a bad temper.^[15]

Interesting facts

Since dobsonfly larvae are intolerant of polluted waters,^[16] though not to the same extent as larvae of mayflies and caddisflies they have a potential to be used as indicators of water quality, though Archichauliodes diversus is not regarded as a ‘clean-water’ taxon.^[17] Invertebrate predators, such as Archichauliodes diversus are competitors with fish, since they eat many of the same prey animals, e.g. Ephcmeroptera, which are an important food source for fish in streams.^[8]

References