Optimal Practices for Rearing Young Mulberry Silkworms

The initial stages of silkworm development, from the first to third instar, are critical in sericulture and demand specific rearing techniques distinct from those used for older larvae. These young silkworms, also known as small or juvenile silkworms, possess unique physiological traits and needs that must be addressed to ensure healthy growth and optimal silk production.

1. Environmental Control: Temperature and Humidity

Unlike older silkworms, young silkworms have a large surface area-to-weight ratio, which causes them to lose heat and water rapidly. As a result, they require a warm and humid environment.

• High Temperature and Humidity: High temperature and humidity within a suitable range help them thrive. This approach is effective as it promotes physiological metabolism and development.
• Low Temperature and Dryness: Conversely, low temperatures and dry conditions can significantly slow down their metabolism, hindering growth and reducing overall vitality, cocoon production, and silk quality.

2. Nutritional Needs: Quality of Mulberry Leaves

Young silkworms require high-quality mulberry leaves to support their fast growth rate.

• Ideal Mulberry Leaves: These leaves should be tender, rich in moisture, carbohydrates, and protein. They should not be too coarse or hard.
• Poor Quality Leaves: Hard or withered leaves will lead to reduced feeding, stunted growth, and weak silkworm bodies.

3. Feeding Management: Ensuring Access to Food

Young silkworms, especially those in their first instar, are small, weak, and have limited mobility.

• Proximity to Food: They can only perceive food within a short range, approximately 5-10 cm. Their movement is also limited, generally 10-40 cm.
• Proper Feeding Technique: Therefore, mulberry leaves must be finely chopped and spread evenly. Avoid excessive feeding to prevent silkworms from becoming lost or buried.

4. Disease Prevention: Maintaining Hygiene

Young silkworms have weaker immunity, making them vulnerable to various diseases.

• Vulnerability to Pathogens: Their susceptibility to diseases like dense nuclear disease, viral softening disease, and aspergillosis is high, especially in their early stages.
• Disinfection is Key: Meticulous disinfection of the rearing environment and equipment is crucial.
• Sensitivity to Gases: Furthermore, young silkworms are highly sensitive to toxic gases like carbon monoxide, sulfur dioxide, and ammonia, which can be detrimental. However, they exhibit a stronger tolerance to non-toxic gases like carbon dioxide.
• Avoiding Contaminated Leaves: Consuming pesticide- or pollutant-contaminated mulberry leaves can cause significant damage, especially during this vulnerable stage.

5. Growth Management: Proper Space and Timing

The growth rate of young silkworms, especially in the first instar, is remarkably fast.

• Rapid Development: First instar silkworms increase their body weight by 12 to 16 times compared to newly hatched larvae. Second and third instars increase by approximately sixfold relative to the previous instar. In contrast, fourth and fifth instars only increase by 4-5 times.
• Adjusting Rearing Space: The area of the silkworm bed needs to be adjusted based on the rapid growth rate and development stage. Timely adjustments of the bed area are essential to ensure even distribution of space and avoid overcrowding.

6. Key Environmental Parameters for Young Silkworm Rearing

The following table summarizes the recommended rearing conditions for young silkworms during different instars. These parameters are crucial for their healthy development.

Note: These values assume a batch of 20,000 silkworms.

7. Historical Evolution of Rearing Techniques

Traditional rearing methods in the early 1950s employed “high temperature drying and multiple thin feeding” techniques. By the 1960s, methods advanced to include dry-proof paper or plastic film coverings, reducing the number of feedings from 10-12 times to 3-4 times daily. In the 1970s, China widely promoted the use of small silkworm kang bed rearing. This technique made it easier to disinfect, heat, and moisturize the rearing environment, leading to significant savings in energy, labor, and mulberry leaves.

By implementing these practices, sericulture practitioners can optimize the growth and health of young silkworms, ultimately leading to increased silk production and quality.