Silkworm Feeding

The silkworm’s acquisition and consumption of food. Whether the silkworm eats food or not depends on whether there are attracting, biting and swallowing substances in the food, and whether there are avoiding substances and so on.

Attracting food is a type of volatile substance that can stimulate the appetite of the larvae and cause the eating action to occur. Such food attractants include β, γ-hexenol, α, β-hexenal and terpenes such as citral, linalol, linalol acetate and terpine acetate. Among these substances, citral and linalol are more attractive. The larvae sense such volatile food quality through the olfactory sensory organs on the antennae.

The quality of the bite is β-sitosterol, isoquercitrin, and phyllin in the mulberry leaves, and the organs that sense these chemicals are the taste organs on the lower palate.

Swallowing substances are mainly cellulose, and others such as sucrose, inositol, phosphate, silicate, chlorogenic acid and vitamin C, etc., also promote the swallowing of food tablets. In addition, the moisture in the feed and the hardness of the feed also have an impact on food intake.

The above-mentioned chemical substances that can induce the feeding action of larvae are not unique to mulberry leaves, but also exist in some plants that silkworms refuse to eat. This shows that the above three types of substances are not all substances that determine the feeding characteristics of larvae. The plant leaves that the larvae refuse to feed also contain repellent substances that suppress their appetite, mainly some alkaloid substances with a bitter taste. On the tumor-like protrusions of the larvae’s lower palate, there are sensillas that are dedicated to sensing bitter and sweet substances. The important reason why larvae have relatively strict selectivity for food is the content of irritant and inhibitory substances in the plant leaves for the above two sensilla.

Larval feeding is intermittent. Every time before eating mulberry, a certain period of exercise or rest should be passed, and only after the appetite occurs can the mulberry begin to eat. Different instars of larvae have different appetite times. Compared with the larvae of different instars, the ant silkworm starts to eat about 20-60 minutes after hatching at room temperature, and it is used for crawling most of the time before eating mulberry. This is the initial hatching. The habit of larva looking for food: the second instar silkworm takes about 80 to 120 minutes, the third instar silkworm takes about 30 to 100 minutes, the fourth instar silkworm takes about 80 to 170 minutes, and the fifth instar silkworm takes about 100 to 170 minutes to start feeding. The silkworm is used for resting and resting most of the time before eating the mulberry, which is conducive to the hardening of the silkworm’s epidermis and the continued completion of the internal organs.

The location of the mulberry varies with instar. The 1st and 2nd instar larvae gnaw from the back of the leaf; the 3rd instar larvae bite from the leaf edge and can eat the finer leaf veins; the 4 to 5th instar larvae gnaw from the leaf edge, leaving only the main leaf vein after eating.

The time and frequency of eating mulberry vary depending on the breeding environment, silkworm instar, variety, and breeding technology. The time spent on mulberry eating for the whole instar accounts for only 27% of the time for eating mulberry. Taking full-age mulberry eating time as 100, the first to fifth instar are 15, 13, 14, 19, and 39, respectively. The number of eating mulberries from 1st to 5th instar is 64, 59, 74, 83 and 183 in sequence. The fifth instar accounts for about 40% of the total number of eating mulberries of the whole instar.

The amount and rate of mulberry leaves eaten increases with instar. A silkworm can eat about 20-25 grams of fresh leaves and 5-6 grams of dry matter. Among them, the food intake of the fifth instar accounted for about 85-88% of the whole instar. The amount of food eaten varies with the species of silkworms and is affected by the external environment. Within a certain temperature range, the amount of food eaten increases as the temperature rises, but decreases when the temperature exceeds this limit. Generally, when the 3rd instar silkworm exceeds 33°C, the 4th instar silkworm exceeds 32°C, and the 5th instar silkworm exceeds 31°C, the food intake decreases instead. Under moderate temperature conditions, the amount of food consumed increases with the increase of humidity, but its influence is not as great as temperature. However, due to humidity, the mulberry leaves are kept fresh. Therefore, adjusting the humidity to maintain the freshness of the mulberry leaves within a suitable temperature range has a positive effect on increasing the feeding amount and feeding rate of silkworms. Leaf quality has a great influence on the amount of nibbling. It is better to ripen leaves, and too old and tender leaves are not suitable. The effect on young silkworms is particularly obvious. Both the feeding amount and the feeding rate are affected by the amount of mulberry given. After increasing the feeding amount within a certain limit, the feeding amount will increase, but the feeding rate will decrease and the residual mulberry will increase.