MATERIALS AND METHODS of NUTRITIVE EFFECTS OF VITAMIN B-COMPLEX ENRICHED MULBERRY LEAVES ON THE SILKWORM, BOMBYX MORI L. (LEPIDOPTERA: BOMBYCIDAE)
MATERIALS AND METHODS
The materials for the present investigation consistent of variety BSRI-95 of silkworm, Bombyx mori L. The eggs of this race were collected from the mulberry silkworm, Germplasm Bank of Bangladesh Sericulture Research and Training Institute (BSRTI) Rajshahi. A brief description of BSRI-95 variety of Bombyx mori L is given below.
It is a high yielding multivoltine variety of silkworm developed at Bangladesh Sericulture Research and Training Institute (BSRTI), Rajshahi. Parents utilized for that race breeding were Nistari and bivoltine (Japan). Since its development the variety becomes very popular to the silkworm rearers for a long time due to high cocoon production and return. Cocoons are yellow, oval with slightly constricted, medium grains; Silk yielding capacity is very high.
B. Life cycle of Bombyx mori L.:
The silkworm, B.mori L.is dioecious i.e, the sex are separate. Fertilization is internal, proceeds by copulation. Development includes a complicated metamorphosis. The duration of the whole life cycle of the silkworm is about 55-60days at temperature of 23-25 C. The life cycle divided into four stages. They are follows:
Eggs: Soon after fertilization, each female lays about 300-500 egg. The female covers the egg by a gelatinous secretion, which sticks them. The small, smooth and spherical eggs are first yellowish white and become darker later on. After laying, the female does not take food and dies with in 4-5 days. In India and other tropical countries, the silkmoth lays non-diapause eggs with continuous growth and development, which enables to rise 2-7 generations within a year.
Larva stage: Larval stage of silkworm divided into five instars and four moultings. Duration times 20 hours.
Pupa: The caterpillar stops feeding and returns to a corner among the leaves. It now begins to secrete the sticky fluid of its salivary glands through a narrow pore, called the spinneret, situated on the hypo pharynx the sticky substance turns into a fine, long and solid thread of silk into the air. The silk thread is made of five filaments stuck together by a gummy substance, the sericin, which is secreted by two other glands. The thread become wrapped the body of the caterpillar forming a pupal case or covering known as the cocoon. This process goes on for about 3-4 days at the end of which silkworm is enclosed with in a thick, oval white or yellow silken cocoon.
Moth: The pupa finally metamorphoses into the baby insect or imago, which secrets and alkaline fluid to moisten on end of the cocoon and then escapes by forcing its way out of the softened silk. Soon after emergence the moths mate, lay eggs and die.
C. Silkworm rearing methods:
Silkworm rearing is a complicated process, which requires various technical aspects, specific management skill, due understanding and experience. The practice of sericulture consists of two major activities, viz. cultivation of mulberry plant for producing disease free leaf crop to the silkworm larvae and the rearing of silkworm larvae to produce the cocoon, which is the raw material for the silk reeling industry. For silkworm rearing a model scientific rearing house is a pre-requisite for a good harvest of quality cocoon crop. The description of the rearing house used in the present investigation is given as follows:
Silkworm rearing demands certain specified environmental condition particularly of temperature and humidity. Hence rearing houses are planned and constructed to provide and maintain proper environmental conditions to get good quality cocoons. The rearing of silkworm was conducted at silkworm research laboratory, Department of Zoology, Rajshahi University which is a satisfactory rearing house. The laboratory measured 7´5 meters and doors were secured with wire-netted shutters and black screens and a air condition to maintain require temperature.
The ceiling of room was quite high and wide fluctuations in environmental conditions outside did not affect seriously the room conditions.
Rearing appliances: The following equipments were used for rearing and mounting of silkworms.
Rearing almirahs: The almirahs were wire-netted to protect the larvae, pupae and adults from parasites and predators like tachinid flies, lizards, rats etc. They measured 1.5´0.7´2.5m.
Rearing trays: Rearing trays are portable receptacles for keeping worms during rearing and wooden rearing trays (40´25´5cm) were used for feeding purposes. There are many kinds of trays differing from one another in materials, shape and size.
Thermometer and Hygrometer: Wet and dry bulb thermometers and were used to record daily temperatures and relative humidity of the rearing room.
Polythene paper and bags: Polythene paper was used to keep the silkworm beds covered during rearing so as to prevent withering of leaf and also to maintain desired humidity in the rearing beds. Polythene bags were used for collecting fresh mulberry leaves and also for keeping the leaves as fresh as possible.
Foam pad: Long foam pads (2.5cm´2.5cm) dipped in water were kept all round the silkworm rearing beds during first two instars for maintaining optimum humidity in the rearing bed (Krishnaswami, 1979).
Antwells: Ants are a serious menace of silkworms. As such it is necessary to rest the rearing almirahs on antwells. During the rearing of the present experiment cement concrete antwells were used.
Chopsticks: Chopsticks are made of bamboo about 17.5cm to 22cm long, thin girth and tapering at one end. They were used for picking the young stage larvae. This ensures hygienic handling of delicate worms, and also prevents damage to them (Ullal and Narasimhanna, 1978).
PLATE – 1
Feathers: White feather were used for brushing newly hatched worms and also changing beds in the early stages. The use of feather during brushing saved the worms from the injuries contact of hand.
Chopping boards, knives and mats:
The chopping board is made of soft wood, with a size of about 0.92cm´0.92cm and a thickness of 7.6cm. For feeding the young silkworm larvae leaves should be chopped. Generally two knives, a smaller one for cutting leaves for young stage worms and bigger one for the latter stages, would be required.
The mats are used at the time of chopping leaves to collect the leaves.
Leaf chambers: Mulberry leaves intended as feed for the silkworms have to be preserved in as fresh a condition as possible. Leaf chamber is intended for this purpose. A simple leaf chamber is made up of a framework of wooden strips, 7.5cm wide, spaced 7.5cm on the sides as also bottom. The chamber will be about 152cm´76cm´76cm high. This is covered on all sides with gunny cloth, which is kept wet. During summer months and also dry days the gunny cloth may be sprayed with water periodically. This helps to prevent the withering of mulberry leaves stored inside the leaf chamber.
Bed cleaning nets made of cotton thread with different mesh suited to the size of the silkworms was used. To remove waste mulberry leaves, faecal matters of silkworms eadavars etc. cleaning nets were employed.
Mountages or “Chandrakis”:
Bamboo made mountages were used for the ripe worms to ensure their spinning of cocoons. They measured 1.8´1.2cm.
Feeding stands with small wooden contrivances having cross legs about 0.95m high were used for keeping the trays during feeding, cleaning etc. Aluminium lids for mating and egg laying, white egg cards, etc. were used. An electronic balance was used for weighting and some beakers were used to prepare solutions.
To prevent various type of disease used lime power as bed disinfectant.
Rearing techniques: The silkworm rearing techniques followed in the present investigation were as follows:
Disinfection: Since silkworms are very much susceptible to diseases, they must be reared under a germ free condition. To prevent diseases and to maintain good sanitation the rearing room and other rearing appliances were disinfected with a 5% formaldehyde solution following the procedure suggested by Ullah and Narasimhanna (1978).
Incubation and disinfection of eggs:
The eggs were incubated at 25°±1°c and humidity 80%±5%. Normal daylight and dark in the night were maintained throughout the incubation period. A black pin-like spot appeared on the egg two days before hatching and on next day it turned completely blue called body pigmentation of the egg.
The eggs at this stage were disinfected with 2% formaldehyde solution for five minutes (Jolly, 1983). Immediately after washing and drying eggs were transferred to the rearing house.
Hatching and brushing: The worms hatch out generally in the morning. During the blue head stage, eggs were preserved in dark until several newly hatched worms were obtained. On the day of hatching eggs were exposed suddenly to a bright light at 8am, which ensured uniform hatching.
The process of transferring of the newly hatched silkworms to rearing tray is called “brushing”. Which was performed with a feather following the brushing technique of Ullal and Narashimhanna (1978). Very finely chopped tender mulberry leaves were spread over the worm for feeding worms. Hatching in first two days was used for rearing.
PLATE – 2
Feeding of the silkworm larvae:
The newly hatched larvae are very active. They constantly use to move until they find mulberry leaves for feeding. On no account the worms were fed on wet, dirty, dusty, diseased, fermented, dried or ripe, yellow leaves nor were the worms given too many leaves at a time.
For the present experiment fresh and succulent leaves were harvested from the mulberry garden of the Department of Zoology, Rajshahi University for feeding the silkworm larvae.
The recommended size of the chopped leaves by Krishnaswami (1979) was followed for feeding early three instars. The fourth and final instar larvae were fed with whole mature leaves. At all stages, the worms were feed four times a day at an interval of six hours, i.e. at 4am, 10am, 4pm and 10pm. There was no feeding during moulting periods. The recommended size of the chopped leaves by Krishnaswami (1979) feeding early three instars, which are given below:
|Age||Size of leaf|
|1st instar||0.5cm – 2.0cm|
|2nd instar||2.0cm – 4.0cm|
|3rd instar||4.0cm – 6.0cm|
|4th instar||6.0cm – 10cm|
|5th instar||Entire leaves|
No food was given during moulting periods.
Bed cleaning: The unconsumed mulberry leaves exevae, dead, larvae, etc. make the bed feverish which injurious the physiology of silkworm, removing of these unwanted matters from the rearing bed is known as bed cleaning.
|Age||No. of bed cleaning||Time of bed cleaning|
|1st instar||1||Before first moult.|
|2nd instar||2||Just after first moult and again before setting for second moult.|
|3rd instar||3||Just after moult in the middle of the age and again before setting for next moult.|
|4th and 5th instar||Daily in the morning.|