YOUNG AGE AND LATE AGE REARING

REARING OF YOUNG (I & H INSTAR) LARVAE

(i) Rearing under Paraffin Paper:

Although, there are several methods of rearing young silkworms but rearing on/under paraffin

paper is more convenient, cheap and popular. In this method, young larvae are placed on a small waste paper sheet which in turn is placed on a praffin paper sheet on a tray (usually of wood) of convenient size and depth (usually 2' x 3'). After providing fresh tender and chopped mulberry leaves, the worms are encircled with moist foam pads. (Plate 13) to maintain the required humidity. This is followed by placing another sheet of paraffin paper over the larvae. This method prevents the mulberry leaves from drying and wilting. During feeding period, the trays are placed on stands or piled one upon the other. Before feeding and during moulting period, the paraffin paper, placed over the worms, is removed so as to get rid of harmful gases and excess moisture.

ii Box rearing

In this method, a thin layer of half burnt damp husk is placed inside a box made of wood, plastic or card board having a size of about 90 x 60 x 9 cm which is enough to accommodate the hatched larvae of 10 g of seed. The rearing box is provided with a lid having small perforations. Brushed worms along with a mulberry leaves are transferred to the box and placed on the damp husk layer. The lid of the box is closed after placing a sheet of paraffin paper on the top. At the time of feeding and moulting, the lid and paraffin paper is removed to allow a mild air current to pass through the box to remove harmful gasses.

3. Wet Cloth Rearing

Here, a moist cloth (usually gunny cloth) is placed over a wooden or plastic tray on which a thin layer of burnt husk is placed. Brushed worms along with the mulberry leaves are transferred to the tray and covered with another piece of moist cloth. The extent of dampness of the cloth depends upon the dryness in the room and external environmental conditions. At the time of feeding and during moult, the moist cloth cover is removed as in the case of paraffin paper or box rearing. This method of rearing is useful for rearing larvae in summer and autumn when temperature is high and humidity low.

In all the three cases, chawki rearing is carried upto the end of the second moult. From third instar onwards, the larvae are reared on trays or shelves without the use of paraffin paper, moist cloth or foam pads as the requirement of humidity decreases with the advancement of age.

4. Cooperative Rearing

In cooperative rearing, collective rearing of young worms is carried out in different forms or units after which the intermediate (third) age worms are dispatched to various farmers for further rearing.

Cooperative rearing is generally conducted in large boxes, usually of wood or plastic (18 x 90 x 15 cm) which are placed in a rearing room where environmental conditions could easily be maintained, Usually, the condition inside the box match those of box rearing and 7 to 8 such boxes, each containing 500 to 1000 g of eggs are placed one upon the other. As a preventive measure against disease, high grade bleaching powder or 5 per cent salisylic acid (95 parts lime and 5 parts salisylic acid) is sprinkled once daily on the rearing bed, usually before the morning feed.

Cooperative rearing is highly economical and profitable as it requires 50 per cent less labour force and leaf requirement than the individual rearing. Thus, a better stability of sericulture is expected thought this method of rearing. However, cooperative rearing demands a well maintained mulberry garden in the vicinity of the rearing house. One of the major drawbacks of this type of rearing is that it somehow, something goes wrong with the rearing, the whole lot gets ruined. Cooperative rearing is not so common in India, however, it is very popular in Japan.

Young larvae require fresh and tender leaves rich in moisture, sugar, proteins and minerals. Th, standard age as well as the quantity and size of the leaf for young age silkworms is given in Table 28- During chawki rearing, feed is provided four times a day. Though, of the total requirement, only 4 to s per cent is consumed during first two instars, yet the rate of growth per given time is the highest in first instar which gradually decreases with the advancement in age. (Aruga, 1994).

TABLE 28. Mulberry Leaf Requirement for Bivoltine/Univoltine Chawki Worms (50,000)

Age of the	Age of the	Leaf qty.	Leaf size	Feeding	Moulting
worm	leaf fed	(kg)	(Sq. cm)	period	period
	(below the tip)			(days)	(h)
1	3rd to 4th	5 to 6	0.5 to 1.0	3.0 to 3.5	22 to 24
II	4th to 5th	15 to 16	1.5 to 2.0	2.5 to 3.0	18 to 20

REARING OF INTERMEDIATE (III INSTAR) AND ADVANCED (IV&V INSTAR) WORMS

The larvae of third instar require environmental conditions that lie in between the young and advanced larvae. Therefore, the conditions for their rearing are suitably adjusted (Table 27). The advanced age larvae, on the other hand, require certain conditions completely different from those of young larvae. Since advanced worms cannot withstand high temperature and humidity, these are, therefore, kept at lower levels than what is provided during chawki rearing (Table 27). High temperature and humidity during advanced ages inversly affect the health of larvae and thereby the produce.

During these ages, emphasis is laid t, provide adequate space and quantity of leaf as well as perform regular cleaning of the bed. Worms are fed three times a day (6 a.m., 2 p.m. and 10 p.m.) on quality mulberry leaves containing less moisture content, more proteins starch and crude fibre. The standard age, size and quantity of the leaf provided to the worms of bivoltine or univoltine breeds is given in Table 28. Being high yielding. univoltine or bivoltine breeds digest and assimilate more food especially in the fifth age, thus require more food and space in comparison to the multivoltine breeds of tropics. The appetite of larvae increases with the age and of the total ingestion during the entire larvae period, nearly 85 pet cent is consumed during fourth and fifth age. The quantity of leaf fed to worms and space required for rearing depends upon the race. However, univoltine/bivoltine races require more space and food than polyvoltine races (Table 29, 30, Plate 14). Generally, advanced worms are reared by the following three methods.

Shelf Rearing

Here, shelves of wooden planks are erected parallel to the wall and one above the other on the stands (Plate 15). The arrangement is made in such a way that besides shelves there is sufficient space for rearer to provide feed and perform bed cleaning. Feed is provided either in the form of entire leaves or shootles and bed is cleaned daily.

This method of rearing is popular in India and main advantage of this rearing is that large number of worms are reared in a small space and it helps in maintaining the hygenic conditions. However, bed cleaning is slightly tideous in this type of rearing.

Floor Rearing

This method of rearing resembles that of shelf rearing except that instead of shelves, worms are placed on a rearing seat made of wood measuring 1 to 1.5 m in width. The seats arc arranged in such a way that good space is left for feeding cleaning.

Shoot Rearing

In this method of rearing, entire mulberry branches or shoots are provided to the worms which are distributed uniformly so that all the worms have equal access to the leaves. Before providing feed, the base and the tip of the shoot is cut so as to made the shoots uniform and avoid immature and overmature leaves in the feed (Plate 16) Shoots are placed close to one another so that worms may not get dropped down and lag behind in feeding. This method of rearing is economical as it reduces the labour used for bed cleaning and feeding as well as the amount of feed by about 25 per cent.

In Japan advanced stages of larvae are reared both indoors and outdoors. The outdoor rearing is usually carried within the mulberry fields at some suitable patches were a tent or shed is erected under which worms are placed (Fig. 71; Plate 17). However, this method is yet to become popular enough since studies required to demonstrate its effectiveness are still underway irrespective of the fact that this method is most convenient and economical.

In the rearing rooms, the air gets polluted by respiration and eagestion of worms. If these pollutants are not periodically removed by allowing the fresh air current to pass through the rooms, the physiology of larvae gets adversely affected. A mild air current during advanced ages considerably Improves the health and cocoon characters of the worm. A dim light of 15 to 20 lux is desirable for advanced worms.