Artificial Incubation of Silkworm Diapause Eggs

In the natural state, diapause eggs will not hatch until the second spring after the low temperature in winter. Since the end of the 19th century, people have adopted various artificial incubation methods to change the natural living environment of silkworms, so that diapause eggs hatch in the summer and autumn of that year, so as to raise silkworms multiple times a year, which has played a great role in increasing the yield of silkworm cocoons.

There are many methods for artificial incubation of silkworm eggs, but there are mainly two kinds of practical applications in production. One is the warm soup seed soaking method invented by China at the end of the 19th century, and the second is the hydrochloric acid incubation method that was discovered by the Italians in 1877 and later improved by China and Japan. The latter is the most widely used.

Hydrochloric acid incubation method

The hydrochloric acid incubation method has 6 major advantages:

• Does not harm the physiology of the embryo in the egg
• High hatchability
• Incubation in one
• Can be incubated at any time
• Large processing volume in a short time
• Less labor and cost

The hydrochloric acid incubation method has been used in China and Japan for more than 70 years. There are instant pickling methods to prevent silkworm eggs from entering diapause and cold storage pickling methods to break diapause.

1. Instant pickling method

Also known as the ordinary hydrochloric acid incubation method, it is a method of protecting the eggs at 25°C for about 20 hours after laying eggs. When the endodermal zone of the eggs is formed, the method is immersed in hydrochloric acid to promote incubation. This method is often used for spring and summer seeds and autumn and late autumn seeds, and the hatching rate can reach 98%.

After the moths are mated in the morning and the pair is removed at noon, 18:00-20:00 is full of eggs, generally 20:00 is the benchmark, and the next day 16:00 is the pickling time. The hydrochloric acid prepared at 15°C with a relative density of 1.075 is heated to 46°C. The pickling time is 4~5min for Chinese species, 5~6min for Japanese species, and 6~7min for European species. Hybrids are based on the female parent. After soaking in acid, wash thoroughly to remove acid, and dry as soon as possible. Flat seed and frame seed production are easy to wash off during the pickling process. The prevention method is to add 2% formalin to the hydrochloric acid solution. After soaking in acid, protect at 25°C for about 10 days, and the silkworms hatch. To postpone the collection of ants, protect them at 25°C for 20h after soaking in acid, and then refrigerate them at 2.5°C. In this case, refrigeration within 20 days will not reduce the hatching rate. Or, 20 hours after spawning, short-term refrigeration of eggs at 5°C for less than 1 week, and pickling treatment at 15°C for 2 hours and 25°C for 2 hours after leaving the warehouse.

In addition to the above-mentioned heating and immediate acid pickling method, there is also a room temperature hydrochloric acid incubation method. The method is to protect the eggs at 25°C for 10~25h after laying, and soak them in hydrochloric acid with a liquid temperature of 25~26°C and a relative density of 1.100~1.120 for 60~80min. This method does not need heating, the equipment is simple, but the immersion time is long, the amount of acid used is large, and the work efficiency is low.

2. Cold storage acid pickling method

The diapause eggs are refrigerated in the early stage of embryonic development, and they are hatched by picking them out of the bank when they need to be seeded. This method uses low temperature to promote the development of diapause eggs in the direction of elimination of diapause, plus hydrochloric acid stimulation to make the eggs obtain hatching function.

This method is used for spring and autumn seeds. The general method is to protect them at 25°C for 42-60 hours after giving birth in spring, and store them at 5°C after embryos develop to the stage of differentiation of the tail section. Judging from the egg color, the criteria for the suitable period of storage and refrigeration are: light red bean color for early autumn seeds, red bean color for mid-autumn seeds, and close to natural colors for late autumn seeds.

Cold storage time: 35~50d for early autumn, 50~75d for mid-autumn, and 75d for late autumn. When leaving the warehouse for acid pickling, it should be exposed to an intermediate temperature of 15°C for 2 hours, and then protected at 25°C for 2 hours before pickling. The relative density of hydrochloric acid is 1.092 ~ 1.094, and the liquid temperature is 48℃. Acid soaking time standard: 5 ~ 6 minutes for Chinese species, 1 chemical, and Japanese 2 chemical eggs; European and Japanese 1 chemical eggs 6 ~ 7 minutes, hybrids take the middle value of the parental standard time.

After acid pickling, if you need to refrigerate again because of adjusting the date of collecting ants, protect it at 25°C for 48h after pickling acid, and then keep it at an intermediate temperature of 12.5~15°C for 12~18h. Then refrigerate at 5°C, and refrigerate for no more than 1 week.