Greenhouse Silkworm Rearing: Key Technical Points and Management Methods Explained

Greenhouse silkworm rearing is a new technology in sericulture production, and it has been promoted and applied in Shandong and Jiangsu for more than 10 years. In our province, trial rearing carried out in Tongxiang, Xiuzhou, Huzhou, Deqing, Shangyu and other cities and counties achieved preliminary success.  All greenhouse silkworm rearing technologies have gradually been spread.

Main advantages of greenhouse silkworm rearing  

First, greenhouses are easy to build, which is conducive to large-scale operation. Greenhouses can be built at field edges, beside houses, or on vacant homestead land, which can solve the contradiction of insufficient silkworm rearing area for large operators.  

Second, investment is low and economic benefits are high. Generally, 1 greenhouse of 200-300 sq m is built for 3-5 mu of mulberry garden, and 5-7 sheets of silkworm eggs can be reared at one time. The investment is about 6,000 yuan or more, while a simple greenhouse requires only about 2,000 yuan. In winter, the greenhouse can be used to grow vegetables, edible fungi, or raise chickens to increase income.  

Third, labor is saved and work efficiency is high. Greenhouse silkworm rearing adopts co-rearing of young silkworms, whole-branch mulberry rearing of grown silkworms, and automatic mounting. According to surveys, 1 laborer can conventionally rear only about 1 sheet of 5th-instar silkworms, but in a greenhouse can rear 2-3 sheets, greatly improving work efficiency. Fourth, people and silkworms are separated, which meets farmers' demands for a higher quality of life and is also beneficial to village and town modernization.  

Greenhouse types and main characteristics  

At present, silkworm rearing greenhouses in our province are mainly divided by structure into 3 types: simple silkworm rooms, greenhouses, and movable silkworm rooms. In Shengzhou City, there is also pit rearing.  

1. Simple silkworm rooms are generally 35 m × 8 m, with walls made of cement bricks, roofs of asbestos tiles, and 2 layers of silkworm stands, costing about 35 yuan per sq m. The main characteristics are long service life, convenient silkworm rearing operations, easy temperature and humidity control, and small temperature differences. However, the one-time investment is large, and comprehensive utilization can only be combined with aquaculture.  

2. Greenhouses can be further divided by materials and structure into 3 types: plastic greenhouses, straw greenhouses, and simple greenhouses.  

① Plastic greenhouses vary in size according to site and rearing quantity, generally 20-25 m × 7-8 m, using assembled galvanized thin-wall greenhouse steel pipes about 22 mm in diameter as arch frames, 0.1 mm thick plastic film as the roof covering material, and then 1-2 layers of shade netting as an insulation layer. Generally, 2 layers of silkworm stands are built, costing about 30 yuan per sq m. The main characteristics are low cost and convenient comprehensive utilization, but high-temperature resistance is relatively poor, and the temperature difference between day and night is also relatively large.

② Straw greenhouses use duck sheds for silkworm rearing in places where duck raising is relatively concentrated. The size is generally 12 m × 8 m × 6 m, with a 1.2 m high brick wall around it and 2 layers of silkworm stands, costing about 20 yuan per sq m to build in rural areas. The main characteristics are easy access to materials, relatively low cost, good high-temperature resistance, and relatively small influence from outside temperature; however, disinfection is difficult to carry out thoroughly, the straw has a short service life, and generally needs to be replaced once every 3-4 years.  

③ Simple greenhouses use vacant land in front of and behind houses. According to the site and rearing quantity, temporary frames are built with wood or moso bamboo against house walls, covered with woven fabric, and dismantled after the silkworm season ends. The main characteristics are convenient construction and labor saving; however, temperature is obviously affected by the outside, and the temperature difference is large.  

3. Movable silkworm rooms are 8.1 m × 7.2 m × 3.8 m, enclosed with expanded perlite boards, with angle iron as flat beams, covered with asbestos tiles, and 2 layers of silkworm stands, costing about 120 yuan per sq m. The main characteristics are easy disassembly and flexible size, but the cost is high.  

4. Pit rearing involves digging a pit in high-lying rice fields, with a size of 13 m × 1.3 m × 2 m, using bamboo strips as frames and covering with straw. Generally, each pit can rear 2 sheets of silkworm eggs. The main characteristics are convenient digging and low cost, but operation is inconvenient.  

Practical techniques for greenhouse silkworm rearing  

1. Site selection: choose flat terrain with smooth drainage, far from rice fields, vegetable plots, and orchards, and relatively close to mulberry gardens to build the greenhouse.  

2. Time of entering the greenhouse: keep the greenhouse dry. For newly built greenhouses, uncover the film during the day to sun the greenhouse, and cover it at night to prevent moisture inside. Before placing silkworms, first lay 1 layer of film on the ground, then lay 1 layer of straw on the film, and place the silkworms on the straw. For co-rearing of instars 1-3, entering the greenhouse on the 4th day of the 4th instar or the 2nd day of the 5th instar is acceptable.  

3. Temperature regulation: greenhouses are generally warmer than indoor silkworm rooms, and the temperature difference between day and night is relatively large. The key to greenhouse temperature regulation is to strengthen ventilation on the basis of good cooling.  

High temperatures can be alleviated through the following measures

① Covering shade materials: covering the roof with shade materials helps lower the temperature inside the greenhouse. Commonly used shade materials include shade netting and grass curtains. For roof coverage with shade netting, the cooling effect of 2 layers is better than 1 layer. The inner layer should be close to the plastic film, and the outer layer should be about 15-20 cm from the roof, and extend out 1.5-2 m on both sides of the greenhouse to form an outer corridor, which is more conducive to preventing direct sunlight on both sides. According to surveys, this method can reduce the temperature inside the greenhouse by 3-4 degrees C. If grass curtains are used on the roof, they should not be too thick, to reduce the roof weight on rainy days. In addition, planting vines around the greenhouse and using green shade can effectively lower the temperature inside the greenhouse.  

② Spraying water on the roof: during high-temperature periods, spray water once every 1 hour starting from 9 a.m. until about 3 p.m. According to surveys, spraying water on the roof can reduce the temperature inside the greenhouse by 1-2 degrees C.  

③ Strengthening ventilation: on sunny days after sunrise, uncover the film on both sides of the greenhouse for ventilation and air exchange. In the evening, when the temperature inside the greenhouse drops below the suitable rearing temperature, lower the film on both sides to keep warm. When temperatures are relatively high, ventilate day and night. On rainy days, lower the shade netting on both sides of the greenhouse and lift the film on both sides to facilitate air circulation.

④ Feeding wet leaves as appropriate: high temperatures inside the greenhouse and ventilation can easily cause mulberry leaves to wilt, so wet leaves can be fed at noon on sunny days, and at the same time spray in the air with 0.3% effective chlorine concentration bleaching powder solution to supplement moisture and prevent disease.  

4. Whole-branch mulberry feeding: greenhouse rearing emphasizes ventilation, and leaf feeding easily causes mulberry leaves to dry out, so whole-branch mulberry feeding is preferable. After the silkworms enter the greenhouse and are given the 2nd feeding of mulberry leaves, whole-branch mulberry feeding can be adopted. Feed mulberry 3 times per day. The amount fed should be based on the characteristics of high rearing temperature and fast development in the greenhouse, feeding enough mulberry leaves in advance. Generally, when about 10% residual mulberry remains, give the next feeding. However, the amount and frequency of mulberry feeding should also be reasonably adjusted according to silkworm development and weather changes.  

5. Disease and pest prevention: carry out pre-rearing disinfection according to conventional methods. For greenhouses used continuously, before using chemicals, first remove about 10 cm of topsoil. After disinfection and before silkworm rearing, first spread 1 layer of chlordane powder on the ground, then spread 1 layer of fresh lime powder. During the silkworm period, spread more drying materials. In rainy, stuffy, and hot weather, use fresh lime powder once in the morning and once in the evening to disinfect the silkworm body and silkworm seat. For rearing in the greenhouse from the 4th instar, remove silkworm droppings and clean the silkworm seat promptly after the 5th instar begins feeding.  

6. Mounting at the proper time: the temperature inside the greenhouse is high, and silkworms mature quickly, so preparations should be made early. One day before seeing maturity, switch to leaf feeding, fill and level the silkworm seat with short straw, and at the same time spray the silkworm body once with silkworm fly control agent. When about 5% are seen mature, begin placing silkworm mounts. Before placing the silkworm mounts, spread 1 layer of fresh lime powder for disinfection, then feed 1 more time with leaves. Pay attention to avoiding mounting when over-mature; otherwise, a large number of mature silkworms will spin cocoons in the silkworm seat and suffer losses. Also pay attention to shading to avoid excessive light increasing losses from cocoon spinning in the silkworm seat.  

Main techniques of greenhouse silkworm rearing  

Because of environmental changes, greenhouse silkworm rearing techniques differ from conventional indoor rearing techniques. On the basis of conventional indoor rearing techniques, the following technical measures should be emphasized: strict disinfection and disease prevention; after entering the greenhouse, it is best to spread fresh lime once a day to keep the silkworm seat dry, while also doing a good job of fly control; handling of silkworm transfer, spreading a layer of fresh lime on the ground, laying a layer of straw or a layer of film, and when transferring silkworms, placing silkworms of the same developmental stage together for future management, with appropriately sparse silkworm density; entering the greenhouse at the proper time, generally co-rearing young silkworms (instars 1-3), and entering the greenhouse on the 2nd day of the 4th or 5th instar. If entering the greenhouse immediately after feeding begins, the newly molted silkworms' poor resistance to the environment will affect their constitution. For those entering the greenhouse at the 4th instar, they can also first be placed on silkworm stands or in silkworm trays for rearing; temperature and humidity regulation, where the key to temperature regulation in greenhouse silkworm rearing is to strengthen ventilation and air exchange on the basis of good cooling, cover with shade netting, skillfully feed wet leaves, use roof cooling, and drain moisture in the rainy season; flexible mulberry feeding, where the amount fed can be appropriately reduced during short daytime intervals and appropriately increased during long nighttime intervals, so that silkworms can eat fully and well; shading during mounting, where attention should be paid to shading when mature silkworms are mounted to prevent the occurrence of failure to spin cocoons, etc.

Greenhouse silkworm rearing is an important technical measure for advancing large-scale sericulture management and realizing sericulture modernization. In Shandong and Jiangsu, it can be said to be a relatively mature technology, but our province has only just started and lacks mature, complete technical experience. Therefore, when applying greenhouse silkworm rearing technology, all localities should grasp it flexibly according to local actual conditions.