Key technical points for summer silkworm (Bombyx mori) rearing

Currently in China's rural areas, there are many people raising silkworms, because judging from the current stage of development in our country, the demand for silk is still quite large; it sells well not only domestically but also abroad. However, in the process of raising silkworms, the points to note in each season differ.

Key points for summer silkworm rearing

Fang Shiyong of the Zhongling team, Tuoshe Village, Shangdu Township, Pingnan County, is an expert silkworm raiser. He planted 2.5 mu of mulberry garden and achieved a bumper summer cocoon harvest for five consecutive years. Notable among these: in 1987 he raised 28.5 sheets of silkworms, with a total fresh cocoon yield of 726.75 kg and total income of 4212.70 yuan. The average output value per mu of mulberry was 1685.08 yuan. His main experience is:

1. Adopt flexible measures to control adverse weather

The hot June in southeastern Guangxi is exactly the rainy season and the high-humidity period, with much rain and heavy moisture, high temperatures, and sometimes sudden clearing and sudden rain with abrupt temperature changes. Therefore, ventilation, cooling and dehumidification during the silkworm rearing period must be strengthened. The methods are: (1) Hot, stuffy weather is most harmful to silkworms about to molt, in the middle of molting, and about to rise from molting, so when rearing middle and large silkworms, the doors and windows of the rearing room should be kept open frequently. In windless weather, use an electric fan to blow air inside the doorway of the rearing room. (2) In hot, dry weather, set up a shade awning outdoors and spray the walls with well water. Give the silkworms more water-containing leaves, feed thin layers frequently, and let them eat fresh leaves at every meal. (3) In low-temperature, high-humidity weather, burn rice straw to raise the temperature and expel moisture, burning for about 10 minutes each time, then open the windows in time to change the air. The silkworm bed should be thin and manure should be cleared frequently. Before picking leaves, scatter rice-straw ash to absorb moisture. (4) In thunderstorm weather, it is stuffy before the rain, so windows must be opened for ventilation and fresh leaves fed. When the thunderstorm arrives, if the wind is strong, close doors and windows in time; after the wind weakens a little, open the doors and windows again to change the air.

2. Strict disinfection and disease prevention

The summer silkworm period has a short cycle for each batch, with much accumulated pathogen and a large spread range. Therefore, each batch of silkworms must be disinfected in time. The method is to first sweep and wash, then disinfect, spraying indoors and outdoors with a bleaching powder solution prepared to a concentration containing 1% available chlorine.

3. Strengthen rearing management

(1) Young silkworms are reared under plastic film coverage, which can keep mulberry leaves fresh and let the silkworms eat their fill.

(2) Summer temperatures are high, so collecting newly hatched ants should be carried out at 7 a.m. and finished within one hour, and leaves should be fed in time. If molting and rising are uneven, they should be reared in batches. To rear large silkworms well, it is advisable to feed thinly and frequently, with a thin bed and full feeding.

Rearing methods for large silkworms  

1. Rearing management: 4th to 5th instar silkworms are called large silkworms. The suitable temperature is 25°C, with a wet-dry difference of 3°C. Usually after the second leaf feed at the first feeding of the 5th instar, the silkworms are moved down to the ground. Before moving the silkworms down, first sweep and wash the ground and disinfect it with bleaching powder. After it dries, spread a layer of lime powder on the ground, then move the silkworms down. Rearing large silkworms requires good ventilation and strengthened disinfection. Disinfect the silkworm bodies and bed with lime powder once a day (before feeding mulberry). Do not pick yellow leaves, muddy leaves, soot-covered leaves or insect-bitten leaves.  

2. Signs of maturity: Large silkworms have a big appetite, so good mulberry and full feeding must be ensured. One sheet of silkworm eggs uses 500 kg of leaves. After 6 to 7 days, 5th instar large silkworms begin to mature. The signs of maturity are: stopping eating mulberry, discharging a large amount of green soft feces, the chest becoming transparent, the body slightly soft and shortened, appearing waxy yellow; the head swinging left and right. This is the suitable time for mounting on the cocooning frame.  

3. Mounting method: For mounting on square cocooning frames, choose 4 to 5 square frames, place them horizontally overlapping alternately, then evenly scatter the mature silkworms onto the frames, and after the silkworms have settled, hang the frames up by hooks. During mounting, keep ventilation good. Generally, spring silkworms can be harvested and sold 6 days after mounting, and summer-autumn silkworms 4 to 5 days after mounting. 

The growth process of the silkworm  

The silkworm is a holometabolous insect. The most common is the mulberry silkworm, which originated in China. Its life goes through several stages: silkworm egg — ant silkworm — mature silkworm — silkworm cocoon — silkworm moth, totaling more than 50 days. After the silkworm moth mates and lays eggs to reproduce offspring, it dies after laying eggs.  

1. Silkworm eggs: The eggs look much like fine sesame seeds, about 1 mm wide and about 0.5 mm thick. One female moth can lay 400 to 500 silkworm eggs. When first laid, they are pale yellow or yellow; after 1 to 2 days they become pale red bean color or red bean color; after another 3 to 4 days they become grayish green or purple and then no longer change. The outer layer is a hard egg shell, and inside are yolk and serosa. The embryo in the fertilized egg continuously takes in nutrients during development and gradually develops into an ant silkworm. It crawls out of the egg shell, and after the shell is empty it becomes white or pale yellow.  

2. Ant silkworm: When the silkworm hatches from the egg, its body color is brown or black. It is extremely small and covered with fine hairs, somewhat like an ant, so it is called an ant silkworm. The ant silkworm is about 2 mm long and about 0.5 mm wide. After crawling out of the egg shell, it will begin eating mulberry leaves after 2 to 3 hours.  

3. Mature silkworm: When the silkworm baby reaches the end of the 5th instar, it gradually shows the characteristics of maturity. First, the feces it discharges change from hard to soft and from dark green to leaf green; appetite declines and mulberry consumption decreases; the front part of the digestive tract is empty, and the chest becomes transparent; then it stops eating completely, the body shortens, and the abdomen also tends toward transparency. The head and chest of the silkworm body raise up, the mouth spins silk threads, and it swings left, right, up and down looking for a place to spin a cocoon. Such a silkworm is called a mature silkworm. 

4. Silkworm cocoon: People place mature silkworms in specially made containers or on mounting frames, and the silkworms then spin silk and form cocoons. Silkworm cocoons come in colors such as white, yellow, pale green and flesh red, about 3 to 4 cm long and 1.7 to 2.1 cm in diameter, with a white surface, irregular wrinkles, and attached silk in a downy form. The silk pattern on the inner wall is very regular, light yet tough, and not easy to tear. An unemerged silkworm cocoon contains 1 yellow-brown silkworm pupa and the pale brown, shrunken silkworm skin shed before pupation.  

5. Silkworm moth: The silkworm moth is shaped like a butterfly and is covered with white scaly hairs, but because its two pairs of wings are relatively small, it has lost the ability to fly. Generally, after mating for 3 to 4 hours, the female moth can lay fertilized eggs. After mating, the male dies immediately, and the female moth takes about one night to lay about 500 eggs, and then also slowly dies.

Silkworm rearing and management techniques  

1. Do a good job of supplementary incubation  

The day before receiving the silkworm eggs, the co-rearing room should be heated to 38°C, with a wet-dry temperature difference of 2°C to 3°C. After receiving the silkworm eggs, immediately spread them evenly on the silkworm bed paper, and raise the room temperature to 43°C, with a wet-dry temperature difference of 1°C to 2°C. Silkworm rooms heated with coal stoves must pay attention to ventilation and air exchange. The silkworm room must be strictly kept dark to make the embryos develop evenly. If the silkworm eggs turn blue relatively evenly, then they can be exposed to light and the ants collected the next morning; otherwise, it is better to expose them to light and collect the ants early in the morning of the 3rd day.  

2. Collect ants at the right time  

If the ants are collected too early, some silkworms do not yet have an appetite at the time of collection, causing uneven mulberry eating. If the ants are collected as they emerge, it will cause uneven development of the silkworms. The most suitable time for collecting ants should be 2 to 3 hours after hatching, when most ant silkworms already have an appetite and begin wandering in search of food. For autumn and late autumn silkworms, collect ants at 8 to 9 a.m., and strive to finish before 10 a.m. If unhatched silkworm eggs are found among the collected ants, continue to keep them in a dark place for protection, and expose them to light and collect the ants again the next day.  

3. Control density  

If the silkworm bed is unevenly thin or dense, it will lead to uneven development of the silkworms. Therefore, before each mulberry feeding, the bed should be expanded and evened out. The requirement is that young silkworms do not touch one another, and large silkworms do not overlap.  

4. Rational leaf use  

In order to promote even development of young silkworms, leaves should be picked and fed according to the leaf-use standard before each instar of the silkworm, avoiding mulberry leaves of uneven old and tender quality. In addition, mulberry feeding should be even in thickness.  

5. Change the position of the silkworm trays in time  

Silkworms in different positions in the same rearing room are affected differently by temperature. For example, the upper part of the rearing rack and places near the heat source have higher temperatures, and the silkworms develop faster; conversely, where the temperature is lower, the silkworms develop more slowly. Therefore, attention should be paid to frequently changing the position of the silkworm trays. During the young silkworm stage, change them at least once a day. 

In the process of raising silkworms, raisers should appropriately adjust their rearing methods and strategies according to seasonal changes. Therefore, to raise high-yield silkworms and produce high-quality silk, one must fully understand the living habits of silkworms.