A Detailed Guide to Silkworm Rearing Techniques and Disease Prevention and Control Methods

1. What should be noted when rearing third-instar silkworms? The third-instar stage lasts about 96 hours, of which about 72 hours are spent feeding on mulberry leaves and about 24 hours in molting. Physiologically, third-instar silkworms are still in the young-silkworm stage; their growth rate is slower than that of the first and second instars, their body weight increases 5 to 6 times compared with the second instar, and their adaptability to high temperatures differs somewhat from that of the first and second instars. During rearing, attention should be paid to:

(1) The rearing temperature during the third instar is best at 25.5°C to 26°C, with a wet-bulb depression of 2°C to 3°C.

(2) The mulberry leaves used in the third instar should be mature leaves and must not be too tender. Feed 4 times a day with cut leaves, and the cut leaves may be appropriately larger. Each batch of eggs uses about 16 kg of leaves.

(3) The rearing bed area is 4 to 4.5 sq m, and six silkworm trays may be used for rearing.

(4) Pay attention to keeping the rearing bed dry; the plastic film underneath may be removed. A moisture-retaining plastic film should still be placed on top.

(5) For litter removal during the third instar, remove litter once each before molting, during molting and after the molt begins, and use No. 1 young-silkworm disease-prevention powder to disinfect the silkworm bodies and the rearing bed.

2. What should be noted before the silkworms molt? Before molting, silkworms should be given good mulberry leaves and allowed to feed fully, and their feeding should be carefully observed.

(1) Feed leaves according to the condition of the silkworms and distribute the mulberry leaves evenly, so that the silkworms both feed fully and leave few leftover leaves, avoiding too many leftover leaves when the molting net is added, which would prevent the silkworms from climbing up.

(2) When adding the molting net, the amount of mulberry leaves given must not be too small, and the edges and corners must be covered, ensuring full feeding before molting so that enough nutrients accumulate in the body to meet the needs of consumption during molting.

(3) Before adding the molting net, the rearing bed should be expanded to the most suitable area to avoid overcrowding; for varieties that develop quickly, the rearing bed should be expanded ahead of time.

(4) Maintain standard temperature and humidity, and do not use high temperatures to induce molting. The temperature during molting is 25.5°C, with a wet-bulb depression of 3°C to 4°C.

3. How should the timing for adding the molting net be determined? When to add the molting net is mainly decided based on the silkworms' feeding time and their body color, body posture and feeding condition.

For the first instar, under suitable temperature conditions, add the molting net after two days of feeding, when the feces are relatively soft, the silkworm body color is parched-rice colored, and the head and thorax are swollen and transparent; the principle for adding the molting net in the first instar is to add it earlier rather than later.

For the second instar, when the silkworms have fed for nearly two days, the phenomenon of silkworms riding on one another generally appears; the silkworm bodies are short and thick, the skin is taut and shiny, and the body color is silvery white. When 0.5% of individuals are seen reaching the pre-molting stage, this is the suitable time to add the molting net.

For the third instar, the suitable time to add the molting net is generally when 1 to 2 molting silkworms are seen.

The suitable time for adding the molting net comes earlier or later depending on variety, instar and rearing temperature. In the young-silkworm stage it should generally be earlier, and in the grown-silkworm stage slightly later; Chinese varieties should be earlier, Japanese varieties slightly later; when the temperature is high and the air dry, it should be slightly earlier, and when the temperature is low and humidity high, it should be slightly later. After adding the net, feed twice before removing litter for molting.