Taxis of Mulberry Silkworm

Silkworms exhibit a range of fascinating behavioral responses, known as tropisms, to various external stimuli such as light, chemicals, and temperature which influence their growth and silk production. These behaviors are essential for their survival and are crucial for optimizing sericulture practices.

1. Phototaxis: The Silkworm’s Response to Light

Phototaxis describes how silkworms react to light. This response can be either positive, moving towards the light source, or negative, moving away. The following table summarizes the typical behavior:

The type of light also matters. Silkworms are most attracted to yellow-green light (490-590 nm), followed by orange, green, and cyan, with the least attraction to purple light. This behavior is very important in sericulture. Uneven light in a rearing room can cause an uneven distribution of silkworms on the feeding beds. Therefore, even lighting is essential and strong or direct light should be avoided.

2. Chemotaxis: Navigating by Scent

Chemotaxis refers to how silkworms respond to chemical stimuli. This is very significant for their feeding and mating behaviors. Silkworm larvae exhibit a positive chemotaxis toward terpenoids like citral and linalol found in mulberry leaves. This allows them to locate and differentiate mulberry leaves from other plants. Furthermore, during mating, male moths utilize the olfactory receptors on their antennae to detect pheromones released by female moths. This allows them to find mates.

3. Denseness: The Tendency to Cluster

Silkworms have a tendency to gather together, which is known as denseness. This is particularly strong in young silkworms. Some varieties, like the Okinawa cocoon silkworms, show strong denseness even when they are mature. This means that they gather in large groups to form cocoons. When rearing silkworms, it is important to ensure that they are evenly distributed on the rearing bed because of this natural tendency.

4. Response to Airflow: Leeward Behavior

While silkworms are not affected by weak air currents, they exhibit leeward behavior when exposed to strong winds. This means they move away from strong winds. The sensitivity to airflow varies depending on their stage of development. Raising silkworms are most sensitive, feeding silkworms are moderately sensitive, and sleeping silkworms are least sensitive. Mature silkworms also seek shelter from stronger winds. Ventilation in the rearing area is needed, but strong, direct airflow should be avoided.

5. Geotaxis: The Preference for Climbing

Silkworms show negative geotaxis, which means they prefer to move upwards. They frequently crawl on the surface of mulberry leaves. When mulberry trees grow, they often climb on the branches. Once mature, silkworms tend to spin cocoons above the middle of the branches. This upward movement is a key trait, and the strength of this response varies between silkworm breeds. European varieties exhibit the strongest negative geotaxis, followed by Chinese varieties, and then Japanese varieties, which show the least.

6. Thermotaxis: Seeking Optimal Temperatures

Thermotaxis is the response of silkworms to temperature. They exhibit positive thermotaxis toward a comfortable temperature range. However, they demonstrate negative thermotaxis by moving away from temperatures above 34°C. It is crucial to maintain an optimal temperature to ensure the health and productivity of the silkworms.

By understanding these tropisms, those involved in sericulture can create environments that promote the well-being of silkworms, which in turn results in higher-quality silk. These behaviors are not just interesting biological phenomena but also critical factors that influence the success of silk production. Whether it is providing the ideal light conditions, ensuring adequate ventilation, or carefully monitoring temperature, every effort contributes to the quality of luxurious silk fabrics produced by skilled artisans.