HST Trustee and mycology expert Peter Buchanan introduces a fascinating fungus named after the island – a fungus that creates zombie caterpillars! Birds and trees are often the first things people think of in relation to Hauturu, so it may come as a surprise to learn there are more species of fungi than species of plants on the island. Ranking by number of species reveals that fungi are Hauturu’s second largest group of land-based organisms, behind fauna (insects, other arthropods, reptiles, birds, etc.). They are followed in third place by the flora. There are certainly many more fungal species yet to be recorded on Hauturu, given only a few fungal studies have been done to date. Around 460 fungal species have been recorded1, which is not a large number. As a mega-diverse kingdom of life, fungi have multiple roles in the ecosystem. They control decomposition and nutrient cycling, and assist most plants’ nutrition and drought tolerance through their associations with plant roots. Fungi also form the dominant biomass of all lichens, while other species act as parasites and cause some diseases. Fungi cannot manufacture their own food, and thus have a multitude of interactions with plants and animals (including us). So what happens when a special fungus and a Ghost Moth caterpillar get together? Our feature fungus was first found as new to science on Hauturu in 1953 and was described scientifically after its island home as “Ophiocordyceps hauturu (Dingley) P.R. Johnst.” Māori knew it as āwheto and its English common name is vegetable caterpillar. Both Māori and English names describe the combined entity of the fungus and its mummified caterpillar host. This fungus is parasitic, and its dispersal spores appear to only germinate and grow by infecting a live caterpillar of two species of Ghost moths in the genera Aoraia and Dumbletonius. These caterpillars live in near vertical burrows in soil and may emerge at night to feed, which is likely when they are most susceptible to infection with O. hauturu spores. Once it enters the caterpillar’s body, the fungus feeds inside its host leading to its death and mummification. At this point, its head faces uppermost in the burrow. An adult hepialid moth with its caterpillars sometimes becoming parasitised by the Ophiocordyceps fungus to become āwheto or vegetable caterpillars. After colonising the caterpillar, the fungus needs to produce its reproductive structure so that its spores can be dispersed above ground. The shortest distance to the soil surface is from the caterpillar’s head. Sensing gravity, a narrow cylindrical fungal fruiting body grows from the caterpillar’s head upwards and beyond the soil surface, broadening somewhat and then differentiating towards its tapered tip. In this upper region, hundreds of flask-shaped structures form within which develop, microscopically, long sacs containing 6-8 ascospores. These spores are released in large numbers, with most dying unless by chance they meet a living Ghost Moth host caterpillar. Three intact āwheto, carefully dug up to show the buried mummified caterpillar linked at its head with the base of the fungal fruiting body. Only the upper half of the fungal fruiting body is initially visible above ground. The fourth (left-hand most) fruiting body separated from its caterpillar during excavation. This fungal species is known from only five collections nationwide, with just the first described specimen recorded from Hauturu. Ophiocordyceps Hauturu is superficially very similar in appearance to the more common O. robertsii. Māori knew both as āwheto, collecting and trading them for use in producing a stable black pigment for tā moko (tattooing). The pigment was produced by burning several āwheto, powdering their charcoal, and mixing it with bird fat. Āwheto may also have been used medicinally for rongoā. Because of its rarity, O. hauturu was evaluated for consideration as an IUCN Red Listed species2, but it was unable to be clearly designated as threatened due to lack of data, rendering its IUCN status as Data Deficient. Further research is warranted to determine its threat status. The related fungal name Cordyceps is well known to teenagers today, thanks to the digital game and recent HBO series entitled “The Last of Us”. The plot involves a global fungal pandemic of humans caused by infection and rapid spread of Cordyceps. Infected humans become zombies, intent on destroying humanity. Although apocalyptic, it is a purely fictional horror movie. 1. Current records are listed in Lyn Wade & Dick Veitch’s 2019 book “Hauturu” pp. 330-342 and Ch. 6.9. 2. https://redlist.info/iucn/species_view/295674/
