MATERIALS AND METHODS of NUTRITIVE EFFECTS OF VITAMIN B-COMPLEX ENRICHED MULBERRY LEAVES ON THE SILKWORM, BOMBYX MORI L. (LEPIDOPTERA: BOMBYCIDAE) -Part Two
Care at moulting:
Moulting is a critical and delicate period in the larval life that needs to be understood very clearly. During the entire larval period the worms moult four times and gradually grow bigger and bigger in size. When at moult, they stop feeding, become motionless, raise head a little and the body becomes shortened.
This stage may last for 24-48 hours. Towards the end the head and foreparts are gradually lowered and finally, the worms begin to stretch their body in an effort to cast their old skin off. By undulatory movements and wringgling, the body completely costs off the skin and becomes free.
The moulting periods, however, depend entirely on the climatic factors, like temperature and relative humidity. The moulted worms look stout and shinny and the head of the worms become dark.
PLATE – 4
Silkworm larvae show a fantastic rate of growth and exhibit a many-fold increase both in weight and size. As a result bed becomes gradually narrower and therefore, bed spacing is required. During the present study bed spacing as recorded by Sengupta (1978) was followed.
|Age of the worms||Time of bed cleaning|
|1st instar and 2nd instar||Length´ Breadth ´ no. of worm ´ 1.02|
|3rd instar||Length´ Breadth ´ no. of worm ´ 2.02|
|4th and||Length´ Breadth ´ no. of worm ´ 3.00|
|5th instar||Length´ Breadth ´ no. of worm ´ 4.00|
Moulting and Harvesting: Towards the close of the final instar larval body becomes translucent and they release soft excreta. At that time the larvae search suitable place for spinning cocoons. The mature worm were collected from the rearing bed and were placed on the bamboo-mad mountages called “Chandrakis”. Soft and watery faces from the mountage were removed by keeping the mountage in an inclined position for two hours. Cocoons were harvested after 4-5 days of mounting.
Segregation of male and female insects:
Pupae are the most convenient stage to identify and to separate males and females. The cocoons were cut open obliquely at one end and the sexes were separated by observing the genital marking at the postero-vental side of the pupae. The presence of a v-shaped genital marking at the ventral side of the last abdominal segment indicates a female pupae and on the other hand, in males a pair of very close dots is found in the same place. Normally the female pupae are larger and heavier than the males. The sexed pupae with their shells were kept separately in paper-made packets to avoid their mixing.
Emergence of moths:
After10-14 days of spinning the adults come out by dissolving one end of the shell as moths. Not more than 5-8 minutes was taken for their emergence and within 45 minutes to an hour, they become fully active and were prepared for mating.
Coupling: After emergence the fresh moths were allowed to mate. Coupled moths were transferred another tray, and left undistributed for six hours under a semi-dark condition. Coupling normally took place between 16-18 hours of emergence and the natural duration for coupling was 24 hours although 3-6 hours are adequate (Jolly et al., 1979). Each couple was then placed on a clean rough paper and covered with an aluminum lid to check them from vivid light and other environmental disturbances.
Egg laying: After 3-4 hours of mating the moths were separated by holding the female moth gently sliding the male anticlock wise with fingers. The female moths were then kept under plastic lids. After complition of egg-laying they were discarded and egg-cards were preserved for next rearing.
Disinfection: Silkworm is very much susceptible to diseases. They must be reared in a germ free condition. To prevent diseases and to maintain good sanitation, the rearing room and the rearing appliances were disinfected with bleaching powder solution following the procedure suggested by Jolly (1987).
PLATE – 5
PLATE – 6
D. Treatment and design of experiment:
Silkworm variety BSRI-95 was used to conduct the present experiment. Fresh leaves were dipped in various concentration of vitamin B-complex, viz. 25, 50, 75, 100 and 125 mg which were dissolved in 100 ml of distilled water, dried up with fan and then chopped. The treated larvae were supplied to the 3rd instars larvae on their first feeding according to present experiment design. Three control lines made on fresh mulberry leaves dipped in distilled water treated were similarly reared. Each concentration including was replicated thrice with 30 larvae each.
E. Collection of data:
Weight of mature larva: The weight of mature larva was taken at 4th and 5th instars, i.e. one day before spinning. Twenty larvae were collected at random from each rearing-bed. Individual weight of these larvae was taken in gram on an electronic balance. A mean of 20 observations for each replication was used for statistical analysis.
Cocoon weight: Cocoons were selected randomly from each replication. Individual weight of 20 cocoons was taken in gram. A mean of 20 cocoon weights was used for analysis.
Pupal weight: To determine the weight of pupae, the harvested cocoons were cut very carefully at one end obliquely with a sharp blade and the pupae were separated. They were then individually weighed on an electronic balance in gram. Mean weight of 20 pupae was considered for statistical analysis.
Fecundity: The total number of eggs laid by the individual female moth was counted. A mean of three laying for each replication was used for statistical analyses.
Hatching Percentage: From computing the hatching percentage, the total number of eggs hatched in laying was counted. Hatching percentage was then worked out by the following formula:
HP = (Total no of eggs hatched in a laying ÷ Total no of eggs in a laying ) × 100
Larval mortality(%): It has been calculated by the following formula