The mulberry silkworm is susceptible to various diseases and is attacked by parasites and pests. Various types of silkworm diseases of larvae are caused by virus, bacteria, fungus and protozoa. These diseases of larvae cause great trouble and loss to the silkworms. So each and every of the silkworm diseases are to be treated seriously, otherwise can create epidemic. There are four major diseases that are caused by parasites and these diseases are :
It is a dangerous disease to the silkworms and the causative organism is the Nosemabombyc is belonging to the phylum protozoa. During the year 1865-70, this disease is first diagnosed by the great Bacteriologist Louis Pasteur. This silkworm disease is transmitted through the egg of the mother silkworm and also through ingestion of contaminated food.
Symptoms of Pebrine:(i) Infected eggs are lacking adhesive gum and so they are easily detached from the card board.
(ii) The larvae become sluggish and dull.
(iii) They have poor appetite and stop feeding.
(iv) The larvae in a rearing tray are of various sizes due to unequal growth.
(v) Infected larvae are lacking lusture.
(vi) In the advanced stage of the disease, there are irregular black spots as pepper grains on the body of the larvae. So the disease is named as pebrine.
Prevention and Control of Pebrine :
(i) After laying of eggs the female moth is crushed and the fluid of the moth is examined under the microscope ; if the spores of the Nosernabombysisare ovserved in the fluid then all the eggs are to be destroyed to control these silkworm diseases.
(ii) Disease free eggs are dipped in a 2% formalin solution for few minutes and then washed in running water for rearing.
(iv) Disinfection of rearing room, frequent inspection of larvae in the rearing tray and destruction of diseased larvae are the general preventive measures.
This disease generally occurs in the mature larvae and caused mainly by bacteria like streptococcus and Staphylococcus.
Symptoms of Flacheria :(i) In this case there is loss of appetite in the larvae.
(ii) The larvae become sluggish and grow slowly.
(iii) The skin of larvae becomes inelastic and softening of body take place.
(iv) In the advance stage of the disease, the larvae vomit liquid material and evacuate loose bowel.
(v) The larvae become motionless, discolored and flaccid.
(vi) The body becomes black and then death occurs.
Prevention and Control of Flacheria:
(i) The diseased silkworms should be isolated from the rearing tray and then destroyed.
(ii) Maintain normal temperature, humidity and ventilation of the rearing room, supply healthy and good leaf as food, avoid overfeeding, avoid overcrowding in the rearing room etc. are necessary to prevent such silkworm diseases.
This disease is caused by a virus.
Symptoms of Grasserie:
(i) In such case of infection the larvae lose its appetite and become yellow.
(ii) The body becomes swollen and shiny.
(iii) The blood of the larvae becomes turbid like pus and when the skin is broken, milky pus flows out which is known as jaundice of the silkworm.
Prevention and Control of Grasserie:
(i) The diseased larvae should isolated from the rearing tray and subsequently the larvae
(ii) Suitable leaves, proper ventilation and spacing are selected for the rearing of silkworm.
These silkworm diseases are caused by a fungus known as Beuveriabassiana.
Symptoms of Muscardine:(i) In such infection the diseased larva loses appetite and as a result it becomes sluggish.
(ii) The body of the larvae becomes stiff.
(iii) The body is covered with white powder like material.
(iv) The larva ultimately becomes dead and appears like a chalky white stick.
Prevention and Control of Muscardine:
(i) The infected larvae are removed and destroyed.
(ii) Good ventilation and normal humidity are to be maintained in the rearing room.
ENEMIES OF SILKWORM
Except such silkworm diseases there have also some enemied of silkworm such as rats, ants, house lizards etc., whenever they got opportunity, they utilize the silkworm as their food material. But these enemies are of minor importance in comparison to pests. The most dangerous enemy of silkworm is the parasitic fly which is commonly known as 'Uzi' fly (Tricholygabombycis). If this fly enters inside the rearing room, the female fly lays eggs on the silkworm larva and after hatching the young maggots of the fly feed on the silkworm larvae. Thus the parasite kills its host and causing heavy damage.
Prevention is to use fine wire-net is to be fitted in the windows and door of the rearingroom, so that the fly cannot enter inside the room. This is only preventive measure against such fly.