Can the precious medicinal material silkworm cordyceps be cultivated artificially? How is it grown? What are the market prospects?
Silkworm cordyceps is a precious medicinal material that has appeared recently. It is a fungus cultivated from silkworm pupae. It is quite popular because of its effects of anti-aging, preventing and treating cardio-cerebral thrombosis, and beautifying the skin. Because it is very difficult to cultivate, most of it is artificially bred. So how is silkworm cordyceps artificially cultivated?
1. Fungal strain
The silkworm itself is not a natural host of cordyceps fungi. Therefore, cultivating silkworm cordyceps requires screening cordyceps strains that have strong infectivity to silkworms and excellent production performance. In the reports so far on successful artificial cultivation of silkworm cordyceps, the strains used are mostly Cordyceps militaris, and no report has yet been seen of successful infection of silkworms by Cordyceps sinensis. Cordyceps militaris has a relatively wide distribution range and is found throughout the country. At present, the strains used in all relevant reports are strains obtained through repeated screening and artificial domestication based on wild cordyceps from various places, and they have good infectivity to silkworms.
Different strain formulations have different infection effects on silkworms. Slant strains, liquid strains and fungal suspensions can all be used to infect silkworms. Wen Lu et al. believe that the fungal suspension prepared by scraping and washing slant strains with sterile water has the best infection effect.
2. Inoculation methods
① Inoculation of live silkworm bodies. Cordyceps militaris is not a pathogenic strain of silkworms, and the digestive fluid in the silkworm gut is strongly alkaline, so cordyceps spores are not easy to survive. Therefore, simple feeding or body spraying cannot effectively infect silkworms. Only puncture inoculation with an insect needle and injection inoculation can infect silkworms with the strain. Wen Lu believes that puncture inoculation has the best effect. However, our test results show that injection inoculation is significantly better than other methods. There is another method of inoculating live silkworm bodies: scatter disinfected silkworm bodies on solid strains, then cover the space containing the insects with the strains, then cover with disinfected plastic film, press the edges tightly, and after about 10 d the cordyceps mycelium can infect the silkworm bodies.
② Inoculation using silkworms as culture medium. This method requires sterilizing 5th-instar silkworms with high-temperature steam and then drying them, adding a certain amount of nutrients, and under sterile conditions using the tissue block method to inoculate the cultured strain onto the body surface of the silkworms, then culturing under sterile conditions, which can also cause the silkworms to become infected. This method is actually equivalent to using silkworms as a culture medium to provide the animal-derived nutrient source needed by cordyceps fungi.
3. Inoculation time
When using silkworms as a culture medium, 5th-instar silkworms are selected. At this stage the silkworm body is relatively large and the nutrition is relatively sufficient. When using solid strains to infect silkworms, 3rd-instar or 5th-instar silkworms are selected. As for the best time for puncture infection of silkworms, there are different views. Some believe that the infection rate is highest at 5th instar 6 d, while others believe that inoculation of newly molted 5th-instar silkworms and 5th-instar 6 d silkworms is both relatively good. Because after newly molting at the 5th instar, silkworms no longer enter dormancy and have an instar period of 8-9 d, which coincides with the disease course, making it the best silkworm age for inoculation; although inoculation at 5th instar 6 d has the highest success rate, after 2-3 d they spin silk and form cocoons, so the silk gland protein cannot be effectively utilized, and the nutritional components and cordyceps weight are affected. In short, silkworms from the 1st to 4th instars are smaller and can provide limited nutrition to the cordyceps fungi inoculated into their bodies, and each instar is shorter. Infected silkworms cannot molt normally during the dormancy period and are prone to infection by other pathogenic bacteria. In contrast, silkworms in the late 5th instar can normally form cocoons before being infected to death, so not only is the silk gland protein in their bodies not utilized by the cordyceps fungi, but it also brings inconvenience to production. Only silkworms in the early 5th instar have large bodies and long instar periods, making them relatively suitable for inoculation.
4. Disinfection methods
The disinfection methods before inoculating silkworms with cordyceps fungi include ultraviolet disinfection and disinfectant disinfection, etc.
5. Symptoms after infection
After silkworms are infected with Cordyceps militaris, there are no obvious symptoms in the early stage. In the early stage after larvae are infected to death, the silkworm body is soft, elastic, with the head and thorax protruding, and there are needle-tip-sized brown small lesions on the body surface. After 2-3 d, the insect body gradually hardens, and white aerial hyphae grow at the intersegmental membranes and spiracles on the body surface. Round conidia are borne on the aerial hyphae.
Market prospect analysis:
Silkworm cordyceps is a kind of cordyceps. It uses silkworm larvae as a culture medium and is artificially cultivated into a kind of “cordyceps”. Its nutritional value is higher than that of pupa cordyceps and relatively similar to wild cordyceps. The success of artificial cultivation of silkworm cordyceps has made up for the insufficient supply and excessively high prices of wild cordyceps, and has provided a new way for the comprehensive utilization of China's sericulture industry. In the future, growing silkworm cordyceps will be profitable.