Diapause vs. Non-diapause Silkworm Eggs

Silkworm reproduces its offspring with eggs, and there are two types of silkworm eggs, diapause eggs and non-diapause eggs. These two kinds of eggs show different biological characteristics even in the same ecological environment.

• After the diapause eggs are laid, when the silkworm eggs develop to a certain stage, although the external environment meets the development requirements, the embryos in the eggs will stop developing and enter a fairly long period of stagnant development. If you don’t come into contact with a certain degree of low temperature, you can’t grow again. Under natural conditions, diapause eggs will not continue to develop until after overwintering (the second spring).
• After the non-diapause eggs are laid, the embryos continue to develop forward, forming larvae and hatching after about 10 days. This kind of silkworm eggs without diapause can hatch without dormancy (within the year).

The first laid eggs are generally pale yellow.

If it is a diapause egg, the egg color will become dark brown with the development of the embryo in the egg after 2 to 3 days, and then it will become thicker, and it will become the inherent color of the species in 4 to 5 days. Because the diapause eggs are dark, they are also called black species. However, the egg colors are purple, gray, brown, green, orange, red, etc., and the most common egg color is purple-gray.

If it is a non-diapause egg, although the embryo in the egg continues to develop, the egg usually remains light yellow-green without changing its color. Generally speaking, egg color can be used as a basis for distinguishing diapause eggs from non-diapause eggs in production. The egg period of diapause eggs is as long as 7 to 10 months, and the egg color is similar to that of the mulberry tree trunk, which may have played a protective role in the wild age.

In the process of entering diapause, the water content of the diapause eggs decreases. Although the environmental conditions change greatly during the subsequent diapause period, the egg metabolism is slow and the egg water content does not change much. The water content will not change significantly until the diapause is relieved and the embryo develops rapidly in the following year. The insensitivity of diapause eggs to environmental changes during the diapause period is particularly obvious in terms of respiratory metabolism. The breathing of a diapause egg is divided into 3 stages:

1. During the embryonic stage, during the first two days and nights after spawning (temperature 24 ~ 26℃), the egg changes greatly, breathing is vigorous, and the CO₂ exhalation volume rises linearly, reaches the maximum breathing volume on the second day after spawning, and then drops rapidly. About 7 days after the egg, the embryo enters the diapause period.
2. The period of diapause is the longest embryo period, generally from the early summer of the current year to the spring of the following year, about 10 months. Seven days after giving birth, although the temperature was 25 to 27 °C at that time, the respiratory volume was still declining, reaching the lowest volume in December.

In the spring development period, in the second spring, the embryos begin to develop after the diapause eggs are released from diapause, and the CO₂ exhaled volume gradually increases. On the 7th day of the greening, the CO₂ exhaled volume is equivalent to the second day after spawning, and continues to increase until The highest amount of egg is reached before hatching. The amount of CO₂ exhaled during embryonic formation and spring development of diapause eggs is affected by environmental temperature and respiratory enzyme inhibitors, while the amount of CO₂ exhaled during diapause is hardly affected by the above two factors.

Non-diapause egg won’t diapause, which the CO₂ exhalation profile of the resting egg spring incubation CO₂ exhalation curve similar to, and likewise affected by factors like temperature.

There is no diapause period for non-diapause eggs, and its CO₂ exhalation curve is similar to the CO₂  exhalation curve of diapause eggs in the spring, and is also affected by factors such as temperature.