Rearing Methods and Technical Key Points for Male Silkworm Larvae

I. New Hybrid Male Silkworm Varieties

(I) Variety Traits. The new autumn-rearing male silkworm variety bred by the Sericulture Research Institute of the Zhejiang Academy of Agricultural Sciences - Qiuhua x Ping 30, has the advantages of a strong constitution, uniform molting and rising at each instar, and being easy to rear. The number of ants per gram is around 2310, the 5th instar takes 6 days and 18 hours, the whole larval stage takes 22 and a half days, the two-day hatching rate is 49.34%, the silk length is around 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.

(II) Key Points of Rearing Technology. For ant reception and light exposure, this can appropriately be done earlier than for common varieties. For labor-saving rearing, the rearing bed should be evenly expanded in good time to prevent uneven mulberry feeding. For older larvae, good-quality mulberry and full feeding are required, and the mulberry used should be fresh and at the proper maturity. The rearing temperature during the young larval stage should be on the higher side, and attention should be paid to keeping the mulberry leaves fresh; during the older larval stage, ventilation and air exchange should be strengthened. The temperature in the mounting frame should be maintained at 25-25.5 degrees 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 Older Larval Stage

(I) Picking, Transporting, and Storing Mulberry Leaves. For spring silkworms, the mulberry used at the 4th instar is picked from third-molt leaves, lower leaves on the branches, and small twigs and leaves; the mulberry used at the 5th instar is picked from bud leaves on new shoots or from branch-cutting leaves. During the summer silkworm season, the mulberry used for older larvae is picked from thinning bud leaves and basal leaves of new branches; during the autumn silkworm season, the mulberry used for older larvae is picked from basal leaves. At the end of late-autumn silkworm rearing, 5-6 leaves are left at the top of the branches.

Mulberry leaves should be transported as soon as they are picked, loaded loosely and transported quickly, and protected from direct sunlight. After arriving at the leaf storage room, they should be poured out immediately, loosened to dissipate heat, and strictly prevented from heating and deteriorating. The leaf storage room still requires low temperature, high humidity, and little air movement, and must be kept clean and hygienic. Shoes must be changed when entering and leaving, and disinfection with 1% available chlorine bleaching powder solution should be carried out at regular intervals. The leaf storage room should be strictly managed, with a dedicated person responsible.

(II) Feeding Mulberry. In feeding male silkworms during the older larval stage, consideration should be given both to full satiation of the silkworms and to saving mulberry to increase the amount of mulberry used per unit. When rearing with bud leaves or leaf blades, feed 3-4 times per day; when rearing with branch mulberry, feed 2-3 times per day. When feeding male older larvae with leaf blades or bud leaves, first loosen the mulberry leaves, then use both hands to spread the leaves evenly over the rearing bed; when feeding branch mulberry, place the tip ends and basal parts alternately in parallel, feeding sequentially from one end of the rearing bed to the other.

(III) Expanding and Evenly Distributing the Rearing Bed. To allow male silkworms to feed fully, the rearing bed area should be expanded in good time during the older larval stage, and attention should be paid to evenly distributing the bed. Generally, for one sheet of male silkworm eggs (30,000 larvae), the maximum rearing bed area during the older larval stage is: about 14 sq m at the 4th instar, and about 35 sq m at the 5th instar. Even distribution of 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.

(IV) Removing Bed Litter. Male silkworms during the older larval stage eat a large amount of mulberry, and the amount of residual mulberry and excrement increases accordingly. To keep the rearing bed clean and dry, bed litter should be removed frequently. Generally, during the 4th instar there is 1 removal at the start and 1 at molting, and 2 intermediate removals, for a total of 4 removals; during the 5th instar, after the initial removal, remove litter once per day. The methods and precautions for litter removal are the same as for common silkworm varieties.

(V) Treatment of Molting and Rising. For male silkworms during the older larval stage, the molting net should be added appropriately later, and the best time to add the molting net is when a few molting silkworms appear in each tray. During molting, the temperature should be 0.5-1 degrees C lower than the rearing temperature, and quietness and even light should be maintained. In the early molting period, keep it dry (dry-bulb and wet-bulb temperature difference 3-4 degrees C); after the silkworms are seen rising, appropriately add moisture to facilitate ecdysis. The time for first feeding after molting is based on the standard that more than 90% of the risen silkworms have a light brown head color; in summer and autumn, because temperatures are high, first feeding after molting may appropriately be advanced. The mulberry used for first feeding after molting still needs to be fresh, and the amount fed should be appropriately controlled, based on about 80% of the largest single feeding amount of the previous instar.

(VI) Rearing Environment. Male older silkworms, like common silkworms, are suitable for growth in a relatively low-temperature and relatively dry environment. Generally, the suitable rearing temperature for 4th-instar silkworms is 24-25 degrees C, with a dry-bulb and wet-bulb temperature difference of 2-3 degrees C; the suitable rearing temperature for 5th-instar silkworms is 23-24 degrees C, with a dry-bulb and wet-bulb temperature difference of 3-4 degrees C. Fourth-instar silkworms should be prevented from being reared at low temperatures below 20 degrees C, and 5th-instar silkworms should be prevented from being reared for long periods at high temperatures above 28 degrees C.