The Effect of Environmental Temperature on Silkworm

The silkworm is a temperature-changing animal. The silkworm lacks a complete system for regulating and maintaining a constant body temperature. The environmental temperature directly affects and basically determines the body temperature of the silkworm. Body temperature affects the metabolism of silkworms, so silkworms are very sensitive to changes in environmental temperature.

The body temperature of silkworms is similar to that of the surrounding environment. Generally, the difference from the air temperature is only within 1.5 ℃. The body temperature before the 4th instar is slightly lower than the air temperature, and after the 5th instar, the body temperature is slightly higher than the air temperature. The body temperature of the 3rd instar is 0.1~0.5 ℃ lower than the air temperature; the 4th instar is 0.3~0.4 ℃ lower, and the 5th instar is 1~1.5 ℃ higher during the full food period.

The body temperature of the silkworm comes from two parts, the inside and the outside. The internal heat comes from the metabolic process. The biological oxidation process of carbohydrates, fats, proteins and other substances in the body provides the energy required for the life activities of silkworms, and at the same time generates heat. The maintenance of silkworm body temperature mainly comes from external heat sources, that is, direct sunlight, indirect radiation and artificial heating of the breeding environment.

The heat loss of the silkworm body can be through the valve and the body surface. Respiration not only causes the silkworm body to exchange gas with the outside, but also exchanges heat with the environment. The moisture escaping from the valve and body surface also takes away a large amount of heat of vaporization and cools the body of the silkworm. Small silkworms are small in size, and in terms of unit weight, relatively large silkworms have a larger body surface area and easily lose heat. This may be one of the reasons why the body temperature of the small silkworm is lower than that of the large silkworm in the same environment.

The adaptability of silkworms to temperature conditions can be divided into 5 temperature zones.

1. Lethal high temperature zone . Due to the high temperature, the silkworms are excited first and then go into a coma. The enzyme system in the body is destroyed and some proteins are coagulated. Silkworms died within a short period of time, and they were unable to recover even if they moved to a suitable temperature zone. The temperature zone is generally 45~50 ℃.
2. Sub-lethal high temperature zone . Unsuitable high temperature makes the assimilation and dissimilation in the silkworm lose the balance, which is manifested by poor growth and development. If the duration is too long, it can also cause thermal coma, and in severe cases, it can lead to death. If you stay in this temperature zone for a short time, you can still return to normal if you move to a suitable temperature zone again. The temperature zone is generally 35~45 ℃.
3. Optimum temperature zone . Life activities are normal in this temperature zone, and the growth and development speed of silkworms is appropriate. This temperature zone is generally considered to be 7~35 ℃. Some people think that the starting temperature of silkworm development is 7.5 ℃, and some people think that it is 10 ℃. The developmental threshold temperature is related to the silkworm stage. Small silkworms are higher, 11.3 ℃ for the first instar; large silkworms are lower, 8.5 ℃ for the fifth instar. The optimum temperature for silkworms is considered to be in the range of 23~29 ℃, and some is considered to be in the range of 24~28 ℃. The optimum temperature for each instar is also different, 25~27.5 ℃ for the first age, 22.5~27.5 ℃ for the 2-4 age, and 22.5~27 ℃ for the fifth age. Considering the effects of temperature on the growth rate, instar elapsed time, mortality and spinning volume of silkworms, it is determined that the most favorable feeding temperature for silkworm rearing is 30 ℃ for 1-3 instars, 25 ℃ for 4th instars, and 20~25 ℃ for 5th instars. .
4. Sublethal low temperature zone . In this temperature zone, the metabolic intensity of the silkworm decreases sharply, and the silkworm is in a coma. In severe cases, body fluids freeze. Silkworms can still resume their activities after moving to a suitable temperature area at this temperature for a short period of time; too long can cause death. This temperature zone is generally 7~ -10 ℃.
5. Lethal low temperature zone . In this temperature zone, a lot of silkworm body fluid freezes and crystallizes, and the protoplasm is dehydrated due to mechanical damage of ice crystals and the physiological function structure is destroyed, causing the silkworm to die. This temperature zone is generally -10~ -15℃.

The response of silkworms to temperature is also different due to silkworm species, developmental stages, nutritional status, physiological status and other meteorological factors.