Parasitic caterpillar fungus in decline

Over-harvesting means 'Himalayan Viagra' may not be available in 10 years' time

PUBLISHED : Monday, 25 March, 2013, 12:00am
UPDATED : Monday, 25 March, 2013, 10:20am

Caterpillar fungus, more valuable by weight than gold and famous for its extensive medicinal use in China for thousands of years, is vanishing and may not be available in 10 years' time, according to a recent study supported by the National Geographic Society.

In a paper published online in this month's edition of Biological Conservation, two researchers from the University of Massachusetts' biology department - Uttam Babu Shrestha and his mentor, Professor Kamaljit Bawa - wrote that the impact of trade and climate change is speeding the parasitic fungus' decline at a startling rate. The decline is so fast, they said, that more systematic conservation efforts may be needed.

Caterpillar fungus, which has been used as a tonic for pain relief and an aphrodisiac for many centuries, is used today as an immunological booster for lung and kidney illnesses, and has a cytotoxic (cell-killing) effect on cancer. It's also a dietary supplement to enhance glucose metabolism, lipid metabolism, energy metabolism, exercise physiology and sexual function.

Up to US$11 billion is spent on the fungus - commonly known as Himalayan Viagra - each year by millions of Chinese hoping to benefit from its supposed effects on male potency. According to Karl Tsim, professor of life science at Hong Kong University of Science and Technology: "No one has strong evidence that it enhances male potency so far, but this is how it is marketed. Here in Hong Kong, it is mostly prescribed to those with asthma or diseases derived from poor immune activity."

The fungus is known by various names. Its scientific name is Ophiocordyceps sinensis; it's known as dong chong xia cao in Putonghua; and yarsagumba in Nepali, which means "winter worm, summer grass".

The natural product of this complex system is the combination of a caterpillar larva and a fungus. The fungus attacks living ghost moth larvae in autumn, killing and mummifying the host by consuming essential nutrients. By early spring, the stalk-like fruiting body emerges from the corpse.

What does this decline tell us about the current environment and global warming?
Professor Kamaljit Bawa

In Nepal, Bhutan and China, it's harvested in the alpine meadows across the Himalayan Plateau. In Nepal, the researchers found that while local harvesters sell the dried worm for US$2.30 to US$7 per piece, traders sell the product to wholesalers or exporters for US$12,000 to US$19,000 per kilogram. In Hong Kong, the retail price of one piece of caterpillar fungus can be as high as US$710.

Tsim doesn't believe there is enough evidence to warrant the use and demand of the fungus. "The price of the wild fungus is so expensive that scientific and systematic research can hardly be carried out, which greatly limits the understanding of its therapeutic effectiveness."

Prices have increased 24-fold over the past 10 years, while trade has declined by more than half since its peak in 2009. Shrestha, one of the Massachusetts researchers who conducted the study in Nepal, hasn't measured the effect on the environment or the economy, but has seen first-hand how the "decline in harvest" is visible all over the Himalayan Plateau.

A reduction in harvesting has also been reported elsewhere in China and in Bhutan. Shrestha interviewed more than 200 harvesters and 28 traders.

"The issue is not what happens if the caterpillar worm declines or disappears," adds Bawa. "The real question is, what does this decline tell us about the current environment and global warming?"

Although Shrestha and Bawa don't believe that one single attribute is responsible for the decline, certainly the combination of factors has had a disastrous effect. Demand and price increases have promoted over-harvesting and premature harvesting by more local collectors who sell to the traders.

Effects of climate change on the Himalayan Plateau - which include less snow, erratic rainfall and an increase in mean temperature - could be affecting the delicate habitats of both the fungus and the insect.

Conservation efforts by local institutions are currently aimed at halting deforestation, taxing harvesting, or strict limitations on harvesting dates, although technical capacity and structural governance is lacking.

The threat of the decline is even more confusing due to a scientific debate related to the terminology, according to Dr Josh Zhu, director of the Beijing Clinical and Pharmacology Centre, Pharmanex.

"The Chinese government listed [the fungus] as a second-grade endangered species. [But] the government did not refer the endangered species to the fungus, because the fungus can be easily cultured or fermented."

Unfortunately, these efforts do nothing to protect the complex host-fungus, as one part of the whole cannot exist without the other.