Why do silkworms form cocoons, and why do some silkworms not form cocoons

It is the instinct of silkworms to spin silk and form cocoons, but it often happens that some mature silkworms do not spin silk and die after a few days, or spit out a small amount of silk without forming cocoons and become naked pupa. In recent years, there are more and more silkworms that do not form cocoons in spring and autumn, and the reasons for this are many.

1) Trace pesticide poisoning.

In the process of feeding, silkworms are exposed to trace pesticides, which paralyzes the central nervous system of silkworms, causing silkworms to spin silk function to be impaired and do not form cocoons. Especially in the second half of the fourth instar exposed to pesticides, there are more silkworms that do not form cocoons or form deformed cocoons.

2) Caused by silkworm disease.

Silkworm diseases are mainly pus, softening and microparticle diseases. The onset of infection usually occurs around the time of the infection. Some pathogenic microorganisms directly invade the silk gland, seriously damaging the secretion function of the silk gland. Or pathogenic microorganisms multiply in the silkworm body, absorb nutrients, affect the normal growth and development of silkworms and the development of silk glands, etc.

3) Physiological effects.

Due to physiological influences such as excessive hypertrophy of the silk glands, silkworms do not form cocoons. The current multifilament varieties are relatively easy to produce non-cocoon silkworms.

4) Bad environment.

One is due to the influence of the undesirable environment in feeding, such as abnormal development of silk glands caused by high temperature and too tender leaf quality, and abnormal development of silk glands caused by exposure to bad gases such as gas, garlic gas, and alcohol. One is the influence of the bad environment in the cocoon, such as the medium and low temperature of the cocoon, which makes the silking time too long or in the case of high temperature and humidity, it will also cause the occurrence of non-cocoon silkworms.

5) Silkworm breed relationship.

There are great differences between varieties of non-cocoon silkworms, and generally there are more non-cocoon silkworms in varieties with more filaments, and varieties with poor resistance to pesticides are also prone to non-cocoon silkworms.

Silkworm cocooning is a self-protective behavior that evolved during the evolution of organisms.

The life of the silkworm will go through several stages of egg-larva-adult-pupa - moth, in the stage of pupation, the silkworm is immovable, and it is easy to be eaten by other animals. In order to protect themselves, silkworms have evolved the ability to form cocoons, using cocoons to wrap pupae to protect them.

After about 4 days after the silkworm has formed a cocoon, it will become a pupa. After about 12 to 15 days, when the pupae begin to soften again, and the skin of the pupae is a little wrinkled and cocoon-colored, it will become a moth.

In order to protect themselves, cocooning can better ensure the chance of becoming a moth.

What is the reason why some silkworms do not form cocoons, and then I will introduce it to you.

1. Pesticide poisoning.

In the process of feeding silkworms, a small amount of pesticides will cause the silkworm spinning function to cause disorders, resulting in the phenomenon of not forming cocoons.

2. Variety. Varieties with a large amount of filaments or varieties with poor pesticide resistance will not be easy to cocoon.

3. Physiological factors.

Physiological factors such as excessive hypertrophy of the silk glands will cause non-cocooning.

4. Surrounding environment.

The feeding environment is too hot, the leaf quality is too tender, and the temperature in the cocoon is too low, which may cause the phenomenon of non-cocooning.

5. Caused by disease.

When silkworms have diseases such as pus, softening and microparticle disease, pathogenic microorganisms will invade the silkworm body, affecting the development of silkworms and the formation of silkworm cocoons.

It usually takes 20-28 days from egg hatching to cocooning. 1st age: 4 to 5 days; Second instar: 3 to 4 days; Third instar: 4 days; Fourth instar: six days; Fifth age: 7 to 9 days.

From the ant silkworm to the first molt for the first instar; After sleeping, it enters the second age; After molting again, it enters the third instar; After the third molt, it enters the fourth instar, and the fourth molt is also known as the big sleep. After sleeping, it enters the fifth age, and the silkworm baby reaches the end of the fifth instar, and it gradually reflects the characteristics of old maturity. People put the ripe silkworms in special containers or on the utensils, and the silkworms spit silk and form cocoons.

The growth and development of silkworms are related to temperature, humidity, food, etc., and it is generally ten to eleven days of green promotion.

The larval stage is about twenty-five days, (specifically four to five days for the first instar stage; 3 to 4 days for the second instar; 4 days for the third instar; 6 days at the fourth instar; Seven to nine days for the fifth in-age period. Pupal stage is 14 to 18 days. The moth period is three to five days.

The feathered silkworm moth no longer eats, and it takes about an hour for the wings to harden. When the wings are stiffened, they will mate their tails.

Each female lays about 300 400 eggs. The purpose of the silkworm feathering into a moth is to mate and lay eggs.

Use mulberry leaves or wheat stalks to make a "hill" look, and they will spin silk on the "mountain" and form cocoons.

When the silkworm baby reaches the end of the fifth instar, it gradually shows the characteristics of old maturity: first, the excreted feces change from hard to soft, from dark green to leaf green; loss of appetite and decreased amount of mulberry eaten; The anterior digestive canal is empty, and the thorax is hyaline; Then the food is completely stopped, the body drive is shortened, the abdomen also tends to be transparent, the cephalothorax of the silkworm body is raised, the mouth is spitting, and the left and right swing up and down to find a place to camp in the cocoon. Put the ripe silkworm in a special container or on a crow, and the silkworm will spin silk and form a cocoon.

Cocoon formation can be divided into four processes: 1. The mature silkworm first spits out the silk and binds it to the cocoon, and then spins the silk to connect the surrounding cocoon branches to form a cocoon bracket, that is, a cocoon net. The cocoon net does not have a cocoon shape, but is just some soft and messy cocoon silk layer to serve as a support for the cocoon.

2. After the silkworm knots make the cocoon net, continue to spit out the messy silk circle, thicken the inner layer of the cocoon net, and then spin the silk in an S-shaped way, and the outline of the cocoon begins to appear, which is called the cocoon coat. The silk fibers of the cocoon are fine and brittle, arranged very irregularly, and have a lot of sericin content. 3. After the cocoon is formed, the cocoon cavity gradually becomes smaller, the front and rear ends of the silkworm body are bent to the back to form a "C" shape, the silkworm continues to spit out the cocoon silk, and the silking method changes from the S shape to form, which begins the process of forming a cocoon layer.

4. When the silkworm has a large amount of silkworm spinning and its body is greatly reduced, the cephalothorax swing speed slows down, and there is no certain rhythm, and the silkworm begins to appear messy, forming a loose and soft cocoon silk layer, which is called a pupal lining.