Detailed Explanation of Silkworm Egg Surface Disinfection Technology, a Must-Read for Silkworm Farmers

The purpose of egg surface disinfection is to kill pathogenic microorganisms attached to the egg surface, avoiding disease in newly hatched silkworms caused by eating the eggshell. For spring silkworm eggs, disinfection is best carried out 1 to 2 days before hatching. For autumn silkworms, it is best done on the afternoon 1 day before hatching, and on that same day the eggs are taken directly to the mountain to hatch.

First, bathe the eggs in a 0.5% sodium hydroxide aqueous solution at a liquid temperature of 18 to 20°C, washing the eggs for 1 minute to remove the adhesive material on the egg surface. Then rinse clean with water, drain off the moisture, and carry out egg surface disinfection. Mix 36% to 38% formaldehyde stock solution, 36% concentrated hydrochloric acid, and water in a ratio of 1:0.5:10 to make a mixed solution at a liquid temperature of 23 to 25°C, and soak the eggs for 30 minutes. Then rinse repeatedly with clean water to remove the chemicals, and spread thinly on plastic mesh to air-dry.

Formaldehyde stock solution produces paraformaldehyde precipitate at low temperatures, which neither dissolves in water nor performs a disinfecting function, so it is ineffective and cannot be used. Commercially sold alcohol and mercury thermometers all have varying degrees of discrepancy, so they must be calibrated before use. The liquid temperature must not be lower than 23°C. Below 23°C, the lower the temperature, the worse the effect. Spring silkworm egg surface disinfection often encounters low-temperature weather; in practice, placing the disinfection container in warm water 1 to 2°C higher than the liquid temperature gives better results. Order of preparing the liquid: pour acid into water, then add formaldehyde and mix well. During disinfection, rub the spring silkworm eggs once every 5 minutes so that the egg surface fully contacts the liquid. For autumn silkworms, first cut off the four sides of the egg-laying paper to enhance the disinfection effect. At the same time, rub off the clustered egg masses on the egg-laying paper and put them into gauze bags to disinfect together. The key step in the disinfection operation is to take 1 sheet of egg-laying paper, place it flat into the liquid with the egg surface facing down, gently press the back of the paper with both hands, and after the entire sheet of egg-laying paper is completely soaked, put in the next batch in the same way until finished. One day before spring silkworm hatching, the egg embryo already has the shape of a silkworm and its respiration increases, so it must be ensured that the eggs dry within 3 hours to avoid the egg pores being sealed by water for a long time, which would cause the embryo to suffocate and die. Personnel who come into contact with disinfected eggs should wear clean clothes beforehand and wash their hands on site to prevent the egg surface from being infected again by pathogenic microorganisms after disinfection.