Rearing Methods and Management Key Points for Male Silkworm Larvae

I. New Hybrid Male Silkworm Varieties

(1) Variety characteristics. The new autumn-rearing male silkworm variety Qiuhua x Ping 30, bred by the Sericulture Research Institute of the Zhejiang Academy of Agricultural Sciences, has the advantages of a strong constitution, uniform molting and rising in each instar, and being easy to rear. The number of silkworm larvae per gram is about 2310, the 5th instar lasts 6 days and 18 hours, the whole instar lasts 22 and a half days, the two-day hatching rate is 49.34%, the silk length is about 1240 m, the cocoon shape is oval, large and uniform, the cocoon color is pure white, and the cocoon shell rate and silk yield are high.

(2) Key points of rearing technology. For gathering newly hatched silkworms, light exposure can appropriately be earlier than for ordinary varieties. For labor-saving rearing, expand and even out the rearing bed in time to prevent uneven mulberry feeding. For grown silkworms, provide good mulberry leaves and allow full feeding, using fresh leaves at the proper maturity. During the young silkworm stage, the rearing temperature should be on the high side, and attention should be paid to keeping the mulberry leaves fresh; during the grown silkworm stage, ventilation and air exchange should be strengthened. The temperature in the mounting frame should be kept at 25-25.5°C, and ventilation and air exchange in the mounting frame should be strengthened to improve the reelability rate.

II. Rearing Management of Male Silkworms During the Grown Silkworm Stage

(1) Picking, transporting, and storing mulberry leaves. For spring silkworms in the 4th instar, pick third-molt leaves, leaves at the lower part of branches, and small branches and leaves; for the 5th instar, pick bud leaves on new shoots or leaves from cut branches. For summer silkworms during the grown silkworm stage, pick thinning bud leaves and leaves at the base of new branches; for autumn silkworms during the grown silkworm stage, pick basal leaves. At the end of late-autumn silkworm rearing, leave 5-6 leaves at the tips of branches.

Mulberry leaves should be picked and transported promptly, loaded loosely and transported quickly, and protected from direct sunlight. After arriving at the leaf storage room, immediately pour them out, loosen them to release heat, and strictly prevent the mulberry leaves from heating up and deteriorating. The leaf storage room should still be kept at low temperature, high humidity, and low airflow, and maintained clean and hygienic. Shoes should be changed when entering and leaving, and disinfection with 1% effective chlorine bleaching powder solution should be carried out regularly. Management of the leaf storage room should be strengthened, with a dedicated person responsible.

(2) Feeding mulberry leaves. When feeding male silkworms during the grown silkworm stage, it is necessary both to consider full feeding of the silkworms and to save mulberry leaves in order to improve the amount of mulberry used per unit. When rearing with bud leaves or individual leaves, feed 3-4 times per day; when rearing with branch leaves, feed 2-3 times per day. When feeding individual leaves or bud leaves to grown male silkworms, first loosen the mulberry leaves, then use both hands to spread the mulberry leaves evenly over the rearing bed; when feeding branch leaves, place the tip ends and base ends alternately and parallel to each other, feeding sequentially from one end of the rearing bed to the other.

(3) Expanding and evening out the rearing bed. To allow male silkworms to feed fully, the rearing bed area should be expanded in time during the grown silkworm stage, and attention should be paid to evening out the bed. Generally, for one sheet of male silkworm eggs (30,000 larvae), the maximum rearing bed area during the grown silkworm stage is: about 14 sq m for the 4th instar and about 35 sq m for the 5th instar. Evening out the bed is also carried out at each feeding, moving silkworms from densely populated areas to sparse areas so that the rearing bed is evenly dense and sparse, promoting uniform development of the silkworm colony.

(4) Removing sand. Male silkworms eat a large amount of mulberry leaves during the grown silkworm stage, and the amount of leftover mulberry and excrement increases accordingly. To keep the rearing bed clean and dry, sand should be removed frequently. Generally, during the 4th instar, remove sand once at the start and once at molting, with 2 removals in between, for a total of 4 removals; during the 5th instar, after the initial removal, remove sand once per day. The methods and precautions for removing sand are the same as for ordinary silkworm varieties.

(5) Handling of molting and rising. During the grown silkworm stage of male silkworms, the molting net should be added appropriately late, with the best time being when a few molting silkworms appear in each rearing tray. During molting, the temperature should be 0.5-1°C lower than the rearing temperature, and quietness and even light should be maintained. Keep it dry in the early molting period (difference between dry and wet bulb temperatures 3-4°C), and after the silkworms are seen rising, add appropriate moisture to facilitate ecdysis. The time for first feeding after molting is based on more than 90% of the risen silkworms having a light brown head color; in summer and autumn, because the temperature is high, first feeding can appropriately be earlier. The mulberry leaves used for first feeding after molting should still be fresh, and the amount fed should be appropriately controlled, based on about 80% of the maximum single feeding amount of the previous instar.

(6) Rearing environment. Like ordinary silkworms, grown male silkworms are suitable for growing in a relatively low-temperature and relatively dry environment. Generally, the suitable rearing temperature for 4th-instar silkworms is 24-25°C, with a dry-wet bulb temperature difference of 2-3°C, and the suitable rearing temperature for 5th-instar silkworms is 23-24°C, with a dry-wet bulb temperature difference of 3-4°C. Fourth-instar silkworms should be kept from being reared at low temperatures below 20°C, and 5th-instar silkworms should be kept from being reared for long periods at high temperatures above 28°C.