Huhu beetle

The first specimen of huhu beetle to be used for taxonomic purposes was collected by British botanist Andrew Sinclair during a voyage in which he visited the Bay of Islands and went on expeditions alongside British botanists William Colenso and Joseph Dalton Hooker. The specimens he collected from this trip were donated to the British Museum (now Natural History Museum of London). From the material Sinclair collected, Scottish zoologist Adam White formally described the species in 1843. The type specimen (the specimen on which the species description is based) is stored in the Natural History Museum of London. Broun then produced a revised description of the species in his landmark Manual of the New Zealand Coleoptera publication in the same year. Phylogeny |align=right|title=Rhipidocerini phylogeny}} A 2023 study examined the phylogeny (evolutionary history) of Australian Rhipidocerini using genomic data produced by shotgun sequencing. The study placed Prionoplus in the Rhipidocerini, a tribe within the longhorn beetles, and positioned it as basal to all other Rhipidocerini species that were sequenced (all of which were Australian species), meaning it split off earlier than the other species that were studied. == Etymology ==

The Māori name is ultimately Austronesian in origin from the root form . Cognates, words in different languages derived from a common ancestor, in the more closely related Malayo-Polynesian languages (like Tagalog ) refer to weevils that infest wood and rice across tropical Southeast Asia. In Māori, has semantically evolved to also refer to its larval form (also , ). As the larva reaches maturity, it ceases to bore in wood and sheds its skin. This stage is known in Māori as . It then develops wings and legs, and while it is still white, it is known as or . Finally, it emerges and flies off to reproduce in its adult stage and is known as . ==Description==

Adult The adult huhu beetle is unmistakable and easily identified by its large size (reaching around in length) and distinctive appearance. Overall, the whole body of the adult is a dark brown colour. The head and thorax have a thick layer of brown hair-like setae giving it a fuzzy appearance. As is typical of longhorn beetles, the antennae are long, extending around three quarters of the beetle's length. The mandibles are large and curved with a sharp end. Spines are present on the femur and tibia, the third and fourth segments of the legs. The elytra (hardened plates that cover the abdomen) is brown and has three pale yellow veins running down the length of the elytra with numerous cross veins forming a reticulated pattern. There is a single record of a female developing an extra pair of ovaries. Pupa The pupa is in length. The head and the pronotum (the main segment of the thorax), are covered in scattered setae, with the pronotum also having a small protuberance at its sides. The mesonotum and metanotum, the second and third segments of the thorax respectively, both have protuberances too, with the former having them in the middle of the segment's end, and the latter having them at the beginning of the segment. The first to eighth segments of the abdomen are covered in short hairs on the upper surface that gradually become more sparse in each consecutive segment. At the end of the abdomen there are two cone-shaped horns that are darkened at their tips. Larva The larva is very large, reaching up to in length before maturation. The mature larva is creamy white and has a robust cylinder shape. The larvae have a well-developed head capsule without any ocelli (simple light detecting organs) and with visible mandibles which are black and shiny. Attached to the head are the antennae, which have three joints. Each segment of the thorax and abdomen is covered in short setae, with the first to sixth abdominal segments having pleural discs (ray-like disc structures that are common in longhorn beetles). The spiracles, openings in the body used for respiration, of the abdomen are also large and easily visible. The first stage larva is identical to the mature larva except for the absence of triangular projections on a few spots of the head. Egg The egg is around in length and wide. It is white and is oval-shaped. The surface is smooth. ==Life cycle==

The huhu beetle deposits clutches of 10–50 eggs (sometimes up to 100) in cracks and crevices in or under bark. During the first instar (developmental stage), the larva burrows into logs and digs longitudinally along the wood's grain, where it makes a small chamber for its first moult. The larva, at various life stages, burrows into the logs form a series of galleries that vary in structure depending on the size and age of the log. In more freshly fallen logs, the galleries formed are fairly straight and do not go very deep. However, as the log rots and more larva feed on the log, the galleries become deeper and more complex in nature, with the tunnels beginning to intersect with those of other larvae. In its final instar the larva moves to within of the surface of the wood before constructing a chamber for the pupal stage by enlarging the diameter of the normal gallery over a period of one to three days. This process creates fragments of wood similar to wood shavings about in size which are then packed into the larval gallery to form a plug. Once the plug is completed the larva lines the walls of the chamber with the last frass (excretions) voided from its gut. The larva then undergoes a resting period of around ten to fifteen days when the abdominal segments contract and the body darkens slightly whereupon it moults into a pupa. The pupal phase lasts around 25 days. Eclosion (when the adult emerges from its cocoon) occurs with a series of ruptures along the head and thorax. The head, legs and wings are freed during arching movements of the body through the ruptured cuticle. The emerged adult may then enter an inactive period of three to five days prior to creating an exit tunnel out of the pupal cavity. The adults are incapable of feeding and lives for roughly two weeks. As adults, the species has a roughly equal sex ratio. ==Hosts==

, one of the hosts of the huhu beetle larva|alt=Two large trees sticking out of the background The larva lives and feeds on the dead wood of gymnosperms. There are fourteen gymnosperm species that are known to act as hosts of the larva. Additionally, there are also two host records of the larva living in tawa and oak, which are angiosperms. However, the latter record is likely a misidentification. Known gymnosperm hosts of huhu beetle larvae: • Kauri • Miro • Mataī • Kahikatea • Rimu • Yellow silver pine • Larch (exotic to New Zealand) • Oregon pine (exotic to New Zealand) • Monterey cypress (exotic to New Zealand) • Pinus spp (exotic to New Zealand), including :* Monterey pine :* Loblolly pine :* Black pine :* Maritime pine ==Distribution and habitat==

The huhu beetle is endemic to New Zealand where it is widespread throughout the main islands, occurring from sea level up to altitudes of . Before Europeans settled in New Zealand, the beetle was mainly associated with podocarp (trees from the Podocarpaceae group) and kauri tree forests, but has subsequently spread more widely due to the introduction of exotic conifers. ==Behaviour==

The beetle is nocturnal and is strongly attracted to light, such as that from human dwellings. During daytime, the beetle hides in crevices or under debris, only becoming active after dusk. The female becomes active earlier than the male, but tends not to travel around as much. After coming out, the beetle will raise its elytra and begin wing movements to "warm up" its flight muscles before beginning to fly. One study recorded flight activity being abundant throughout the night until 2am before ceasing between 4–5am. The adult female apparently produces an olfactory cue which attracts the male, with the male seemingly flying more frequently to detect the female. The adult of both sexes will exhibit a display behaviour if disturbed with the head jutting forward, mandibles opening to their full extent, antennae flailing and the head being raised and lowered. When anything touches the mandibles, it can deliver a bite and will latch onto the object. The beetles escalate conflicts with each other into combat by grappling with their forelegs, typically throwing one opponent onto its back. Any object coming into contact with the mandibles is seized frequently resulting in the loss of appendages. Usually, the male copulates with the female between 10 pm and 1 am. This begins when the male approaches the female from behind and mounts it while gripping its thorax with the middle and rear legs. If successful, both beetles become somewhat inactive, with both sexes antennae twitching and with the male mandibles stimulating the female's upper surface, a process which may last up to fifteen minutes. The pair then begin to copulate, which may take up to twelve minutes. ==Gut microbiome==

'' are found in the gut of huhu beetles.|alt=Grey coloured microorganisms that are circular in shape In one study, the digestive tract of the huhu beetle was found to harbour a diverse range of microorganisms such as Acidobacteriaceae, Burkholderiaceae and Enterobacteriaceae. It was inferred that a large proportion of the microorganisms detected likely assists in the digestion process. The gut microbiome diversity is dependent on the food source the larva has access to. When fed on a diet of just cotton, a cellulose rich food source, the gut microbiome develops a high abundance of cellulose degraders. Conversely, when given a diet of pine wood, the gut microbiome had a high level of microorganisms such as Scheffersomyces, which are known to digest plant cell walls. ==As food==

The huhu larva is eaten by humans, with a long history of consumption by Māori. Its flavour has been described as like peanut butter. The fully grown larva (called in Māori) is the most prized because there is no undigested wood pulp inside of it anymore. Huhu grubs may be consumed either raw or traditionally cooked in a . It has been proposed that huhu larva could potentially be farmed as a food source, but challenges such as maintaining genetic diversity and uncovering optimal growing conditions need to be investigated to see if this would be viable. P. reticularis contains substantial amounts of nutrients. The larva and pupa are relatively high in fat (up to 45% and 58% dry weight in large larvae and pupae respectively). The fat in the larva is mostly oleic acid and palmitic acid. ==Predators==

, which preyed upon huhu beetles|alt=A painting of a pair of HuiaThe beetle preyed upon by a wide range of predators. Some such predators are introduced to New Zealand, such as ship rats, little owl and magpie. Native predators include short-tailed bats, moreporks and saddlebacks. Before their extinction, huia were observed to utilise huhu beetle larvae as their principal food source. The larva is preyed upon by the larva of Thoramus wakefieldi, a species of click beetle, despite the relative small size of T. wakefieldi when compared to huhu larva. The larva is also preyed upon by Rhipistena cryptarthra, a species of wedge-shaped beetle. Parasites It is the only known host of Prionaphes depressus, a parasitoid species of fairy wasp that lays its offspring in the eggs of the huhu beetle. The beetle may also become infected with Beauveria, a parasitic fungus that infects insects. The infected beetle is generally killed by the fungus during the pre-pupal or pupal stage. The fungi generally infect 1 in 1,000 beetles, but this varies by location. The parasitic protozoan Gregarina has also been recorded infecting the larva. ==Forestry pest==

Because the larva feeds on logs, it is considered a forestry pest. In New Zealand, logs that are to be exported overseas are legally mandated to first be treated with a fumigant, such as methyl bromide, or heated to prevent the beetles (among other insects) from accidentally being exported and introduced to other countries. Because of this, treatment methods must be able to penetrate deeper into the logs. , methyl bromide is still used to treat logs, but cyanogen is now also used as an alternative fumigant. Heat treatment is also used. ==See also==