The silkworm pupa is the intermediate stage of the domesticated silk moth (\(Bombyx mori\)). The insect undergoes a four-stage life cycle: egg, larva, pupa, and adult moth. The pupal stage occurs inside the silk cocoon, which is harvested to produce raw silk. Once the silk filament is reeled off, the pupa remains as a substantial byproduct of the textile industry. Due to its rich composition, this byproduct is now gaining global recognition, transforming it from a waste material into a valuable resource.
The Pupa Stage in the Silkworm Life Cycle
The pupal stage is a period of complete metamorphosis, occurring after the larval stage and before the emergence of the adult moth. The mature silkworm larva spins a protective silk cocoon around itself, transitioning into the pupa, also known as a chrysalis. Although the pupa appears motionless, this is a time of intense biological reorganization where larval tissues break down and structures for the adult moth, such as wings and antennae, develop.
This transformative stage typically lasts between 8 to 14 days. To harvest the long, unbroken silk filament necessary for commercial textiles, the pupa must be killed, or “stifled,” inside the cocoon. Stifling, often done by heat or boiling water, prevents the pupa from emerging as a moth, which would secrete an alkaline fluid and break the silk threads. This process preserves the integrity of the silk and makes the pupa available as a byproduct.
Utilization as a Protein Source and Byproduct
The silkworm pupa is a major byproduct of the sericulture industry, especially in high-volume silk producing countries like China, India, and Korea. This material is widely repurposed as an inexpensive and sustainable protein source in various commercial applications. In many Asian cultures, the pupa is consumed directly, a practice known as entomophagy, where it is prepared as a snack or dish. This direct human consumption provides a high-quality protein source without the environmental burden of traditional livestock farming.
The pupa is also heavily utilized in animal feed, offering an alternative to costly protein supplements like fishmeal and soybean meal. Processed pupa meal is an effective ingredient in aquaculture for feeding fish and crustaceans, and in diets for poultry and pigs. This use reduces sericulture waste and helps lower feed production costs.
Furthermore, the pupa serves as a source for extracting specialty compounds for non-food industries. The pupa’s oil, sometimes called chrysalis oil, is extracted for use in cosmetic and medicinal applications due to its emollient and antioxidant properties. Specific proteins and bioactive peptides are also isolated for potential use in health supplements, including research into traditional medicine applications for conditions like hypertension. Maximizing the use of the pupa increases the economic value of sericulture, promoting a circular economy approach.
Key Nutritional Components
The composition of the silkworm pupa makes it a highly nutrient-dense food and feed ingredient. The crude protein content is remarkably high, often ranging from 50% to over 65% of its dry mass, comparable to or exceeding many conventional protein sources. This protein is high-quality because it contains all 18 amino acids, including the essential amino acids.
Lipids constitute another significant portion, with crude fat content typically between 20% and 35% of the dry weight. The extracted oil is valuable because up to 80% of its fatty acids are unsaturated, including Omega-3 fatty acids like alpha-linolenic acid. These fats contribute to its use in functional foods and supplements. The pupa also contains a variety of micronutrients, including B-complex vitamins, Vitamin E, and minerals such as potassium, zinc, iron, and calcium.