Growth of Mulberry Silkworm

The growth process of silkworm body and its parts and organs in weight and volume in the larval stage of silkworm. During the entire development process of the silkworm from egg to adult, only the larvae ingest food and grow rapidly. The larvae absorb nutrients from food and supply energy through material metabolism to build a silkworm body. With the increase and increase of the cells in the body, the body weight and volume increase. Among the cells that make up the various organs and tissues of silkworm bodies, for example, although the number of blood cells increases with the development of silkworms, there is no difference in the size of blood cells between small silkworms and large silkworms. On the contrary, such as silk glands, martens tubes, salivary glands and molting Cells such as glands do not divide but each cell grows up gradually. There are dermal cells of the body wall, epithelial cells of various organs and fat body cells that can divide and grow up.

The growth rate of silkworms varies with silkworm species, feeding period, feeding temperature and feed quality. When the silkworm larvae grows from the ant silkworm to the extreme (the fifth instar food period), the body weight increases up to 10,000 times. The body weight increase rate of each instar is the largest in the first instar (Table 1). The weight of the second instar silkworm is about 12 times higher than that of the ant silkworm. The weight of the third instar silkworm is about 6 times higher than that of the second instar silkworm. reduce. The growth rate in an instar period is also greater in the early period than in the later period. The growth multiple of male silkworms is larger than that of female silkworms. Among the varieties, the Japanese line is the largest, the Chinese line is the second, and the European line is the smallest. If the body weight of the silkworm larvae measured daily during the whole instar or one instar period is connected into a curve, it is roughly in an “S” shape, that is, the growth of the silkworm larvae has a certain regularity. When the ant silkworm grows extremely to the 5th instar, the body length increases by 23-28 times, the body width increases by 17-21 times, the body surface area increases by about 500 times, and the increase in volume and weight is the same, about 10,000 times.

The growth rate of the head and body of the larvae is significantly different. The head of the young silkworm is relatively larger, and the head becomes smaller as it grows. In one instar, the head of the silkworm is also larger, but the head is smaller in the full feeding period.

The increase in silk gland weight is far greater than body weight. In the first instar, the weight of silkworms is about 10 times higher than that of ant silkworms, 80 times in the second instar, 560 times in the third instar, 2,500 times in the fourth instar, and 10,000 times in the fifth instar. The weight of silk gland is 20 times that of ant silk glands in the first instar, 120 times in the second instar, 600 times in the third instar, 4,000 times in the fourth instar, and 160,000 times in the fifth instar. The percentage of silk gland weight in silkworm body weight is below 5% from the first to the fourth instar. The silk gland increases rapidly in the fifth instar, and accounts for 40-45% of the silkworm body weight when the silkworm matures. The growth of silk glands is due to the enlargement of silk gland cells and the increase of the accumulation of silk material secreted by it. Silk gland cells not only grow rapidly in the mulberry, but also in the early stage of sleep and on the mulberry, their cell growth does not stop. The length of silk gland increases 50 times from 1 to 5 years, and its thickness increases 57 times

In the pupal stage, the ovary grows rapidly and develops significantly. Although its growth degree varies with silkworm species and feeding conditions, it still grows in an “S” curve. The growth of the ovary is the fastest in the middle stage of the pupae, especially the first half of the middle stage, and gradually weakens in the later stage. The degree of ovarian growth has a great relationship with the amount of eggs laid and whether the contents of the eggs are sufficient. It is not only related to the performance of contemporary seed collection, but also affects the vitality and breeding performance of the next generation of silkworms.

The 9 pairs of air valves of silkworm larvae differ in size from the ant silkworm at the time of hatching. The first, eighth and ninth pairs of air valves are relatively large, and the other pairs are slightly smaller. The growth rate of each valve is also different. From the third pair to the eighth pair, the six pairs of valves grow faster, which is closely related to the growth of silk glands. From the perspective of the whole age, the growth multiple of the air valve is significant at the small silkworm stage and relatively small at the large silkworm stage. The growth of body weight is faster than the growth of the air valve, so the ratio of air valve to the silkworm body is relatively small. This causes difficulties in water dispersion and gas exchange for the silkworm stage. Therefore, the silkworm rearing environment in the silkworm stage should be slightly dry and breezy. In order to ensure better growth of silkworm larvae.