Ophiocordyceps sinensis (यार्सागुम्बा)

Ophiocordyceps sinensis or Yarsa-gumba, Yarsha-gumba or Yarcha-gumba, यार्सागुम्बा is an entomopathogenic fungus  in the family Ophiocordycipitaceae. It mainly found in the meadows above 3,500 meters  in the Himalayan regions of Nepal, Bhutan, India and Tibet. It parasitizes larvae of ghost moths and produces a fruiting body which used to be valued as a herbal remedy. However, the fruiting bodies harvested in nature usually contain high amounts of arsenic and other heavy metals so they are potentially toxic and sales have been strictly regulated by the CFDA  in 2016.

O. sinensis parasitizes the larvae of moths within the family Hepialidae, specifically genera found on the Tibetan Plateau and in the Himalayas, between elevations of 3000 m and 5000 m. The fungus germinates in the living larva, kills and mummifies it, and then a dark brown stalk-like fruiting body which is a few centimeters long emerges from the corpse and stands upright.

It is known in English colloquially as caterpillar fungus, or by its more prominent names yartsa gunbu, or dōng chóng xià cǎo .

O. sinensis is classified as a medicinal mushroom, and its use has a long history in traditional Chinese medicine as well as traditional Tibetan medicine. The hand-collected, intact fungus-caterpillar body is valued by herbalists as medicine, and because of its cost, its use is also a status symbol.

This fruiting bodies of the fungus are not yet cultivated commercially, but the mycelium form can be cultivated in vitro. Overharvesting and overexploitation have led to the classification of O. sinensis as an endangered species in China. Additional research needs to be carried out in order to understand its morphology and growth habits for conservation and optimum utilization.

Taxonomic history and systematics

Morphological features

O. sinensis consists of two parts, a fungal endosclerotium and stroma. The stroma is the upper fungal part and is dark brown or black, but can be a yellow color when fresh, and longer than the caterpillar itself, usually 4–10 cm. It grows singly from the larval head, and is clavate, sublanceolate or fusiform, and distinct from the stipe . The stipe is slender, glabrous, and longitudinally furrowed or ridged.

The fertile part of the stroma is the head. The head is granular because of the ostioles of the embedded perithecia.

The English term “vegetable caterpillar” is a misnomer, as no plant is involved. “Caterpillar fungus” is a preferred term.

Nomenclature of the anamorph

Since the 1980s, 22 species in 13 genera have been attributed to the anamorph  of O. sinensis. Of the 22 species, Cephalosporium acreomonium is the zygomycetous species of Umbelopsis, Chrysosporium sinense has very low similarity in RAPD polymorphism, hence it is not the anamorph. Likewise, Cephalosporium dongchongxiacae, C. sp. sensu, Hirsutella sinensis and H. hepiali and Synnematium sinnense are synonymous and only H. sinensis is only validly published in articles. Cephalosporium sinensis possibly might be synonymous to H. sinensis but there is lack of valid information. Isaria farinosa is combined to Paecilomyces farinosus and is not the anamorph. Several isolates of Isaria sp., Verticella sp., Scydalium sp. and Stachybotrys sp. were identified only up to generic level, and it is dubious that they are anamorph. Mortierella hepiali is discarded as anamorph as it belongs to Zygomycota. Paecilomyces sinensis and Sporothrix insectorum are discarded based on the molecular evidence. P. lingi appeared only in one article and thus is discarded because of incomplete information. Tolypocladium sinense, P. hepiali, and Scydalium hepiali, have no valid information and thus are not considered as anamorph to Ophiocordyceps sinensis. V. sinensis is not considered anamorph as there is no valid published information. Similarly, Metarhizium anisopliae is not considered anamorph as it has widely distributed host range, and is not restricted only in high altitude.

Thus Hirsutella sinensis is considered the validly published anamorph of O. sinensis, Cordyceps nepalensis and C. multiaxialis which had similar morphological characteristics to O. sinensis, also had almost identical or identical ITS sequences and its presumed anamorph, H. sinensis. This also confirms H. sinensis to be anamorph of O. sinensis and suggests C. nepalensis and C. multiaxialis are synonyms. Evidence based on microcyclic conidiation from ascospores and molecular studies in alpine grass and shrub-lands on the Tibetan Plateau and the Himalayas at an altitude between . The fungus is reported from the northern range of Nepal, Bhutan, and also from the northern states of India, apart from northern Yunnan, eastern Qinghai, eastern Tibet, western Sichuan, southwestern Gansu provinces. During late summer, the fruiting body disperses spores. The caterpillars, which live underground feeding on roots, are most vulnerable to the fungus after shedding their skin, during late summer. In late autumn, chemicals on the skin of the caterpillar interact with the fungal spores and release the fungal mycelia, which then infects the caterpillar.

The slow growing O. sinensis grows at a comparatively low temperature, i.e., below 21 °C. Temperature requirements and growth rates are crucial factors that identify O. sinensis from other similar fungi. The entire fungus-caterpillar combination is hand-collected for medicinal use.

In traditional Chinese medicine, it is regarded as having an excellent balance of yin and yang as it is considered to be composed of both an animal and a vegetable. They are now cultivated on an industrial scale for their use in TCM. However, no one has succeeded so far in rearing the fungus by infecting cultivated caterpillars; The Himalayan Ophiocordyceps production might not exceed a few tons.

In 2004 the value of a kilogram of caterpillars was estimated at about 30,000 to 60,000 Nepali rupees in Nepal, and about Rs 100,000 in India. In 2012, a pound of top-quality yartsa had reached retail prices of $50,000.

The price of Ophiocordyceps sinensis is reported to have increased dramatically on the Tibetan Plateau, about 900% between 1998 and 2008, an annual average of over 20% . However, the value of large caterpillar fungus has increased more dramatically than small Cordyceps, regarded as lower quality.

Its value gave it a role in the Nepalese Civil War, as the Nepalese Maoists and government forces fought for control of the lucrative export trade during the June–July harvest season. Collecting yarchagumba in Nepal had only been legalised in 2001, and now demand is highest in countries such as China, Thailand, Vietnam, Korea and Japan. By 2002, the ‘herb’ was valued at R 105,000  per kilogram, allowing the government to charge a royalty of R 20,000  per kilogram.

The search for Ophiocordyceps sinensis is often perceived to threaten the environment of the Tibetan Plateau where it grows. While it has been collected for centuries and is still common in such areas, current collection rates are much higher than in historical times.

Cultivated O. sinensis mycelium is an alternative to wild-harvested O. sinensis, and producers claim it may offer improved consistency. Artificial culture of O. sinensis is typically by growth of pure mycelia in liquid culture  or on grains .

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