FLACHERIE

FLACHERIE

Flacherie or rot or wilt disease constitutes the three common bacterial diseases viz. bacterial rot of digestive organs, septicimia and sotto disease. The pathogens of flacherie other than that of sotto disease has not yet been clearly identified but it has been found that bacteria effect the worms which are physiologically weak. Swamura, 1905 believed a that flacherie is caused by several bacteria which occur commonly on mulberry leaves. Worms affected by flacherie become sluggish and soft, vomit clear brownish fluid and pass softer faeces. Finally, the trunk turns black (Plate 30) and worms hang by anal claspers with head downwards,body putrifies and falls down in a semi liquid condition having foul odour. When the larvae are afflicted with flacherie, their nature of haemolymph and digestive fluid also changes; the haemolymph shows a decrease in its refractive index and pH which reaches to 7.0 (Aruga, 1994),

BACTERIAL DISEASE OF DIGESTIVE SYSTEM 
Causal organism : (i) Streptococcus spp.   (ii) Diplococcus spp. 

This is called shrinking disease because infected larvae get shrunken in size and become dull black particularly in freshly moulted state. The worms get infection through contaminated leaves.It is believed that bacteria effect those worms having weak metabolism thereby weak sterilizing power of the digestive tract. When bacteria enter the gut, they multiply rapidly, take nutrition from the gut wall cells which results in their degeneration. The degeneration of cell types depends upon the type of bacteria. If the multiplying bacteria are Streptococcus species, the cylindrical cells degenerate and if Diplococcus species, the goblet cells degenerate (Ganga and Chetty, 1997). The symptoms of this disease usually appear when worms are full grown. They become sluggish, motionless, vomit clear brownish liquid, pass excrements of irregular shape, skin becomes black, body softens and putrifies.It has been found that the diseased worms have an acid gut. The bacteria of this disease have also been found associated with CPV.

SEPTICIMIA 

Causal organism : (i) Staphylococcus aureus   (ii) Streptococcus bombycis

Infection of septicimia spreads mainly through entry of the bacterium into the body cavity of the worm via wound or injury and rarely through ingestion of the pathogen. Pupae and moth, which do not feed, are also affected with septicimia. Penetration and multiplication of bacteria in the haemolymp cause speticimia.
Infected larvae shrink, become inactive, pass softer faces, lose appetite, show retarted growth, vomit fluid, lose clasping power and finally die. After death, larvae turn dark brown or greyish black. Depending upon the type of bacterial infection, the dead larvae may or may not emit foul odour. In general, intestine part of the body may be swollen and posterior part shrunken (Plate 31) (Krishnaswamiet al., 1987). Infected pupae and moth also exhibit similar symptoms.

SOTTO DISEASE 
Causal organism: (i) Bacillus Thuringiensis var. Sotto  (ii) Bacillus bombycis

Infection spreads mainly through contaminated leaves. The disease is also known as toxicosis as the pathogen after infecting the host produces crystals of toxin which results in the death of the host (Aruga, 1994). The shape and sizeof the crystals vary from strain to strain but usually its size is 0.6 x 2. The toxin produced gets dissolved in alkaline gastric fluid and absorbed through the gastric wall. The toxin changes the pH of haemolymph (from 9.0 to 10.5) resulting from changes in the permeability of the gut (Aruga, 1994). It affects the nervous system of host and paralises it. The toxin is stored in a parasporal crystalline body formed at the time of sporulation. The endotoxin of this parasite is known as thuricide and is available commercially as a bio control agent for other lepidopteran pests (Ganga and Chetty, 1997).
Before death, the diseased larvae become sluggish, shrink, suffer from diarrhoea, lose clasping power of the legs and vomit yellow fluid. After the death, body turns black and internal organs get liquified, skin becomes fragile which ruptures sending out foul smell of rot (Ganga and Chetty, 1997).

In general, flacherie diseases change the nature of the haemolymph and digestive fluid of the larvae. The amount of free amino acids and antibodies in the haemolymph get reduced.

RANGI DISEASE

Causal organism : Serratia marcescene
This disease is known as Court in Europe and Rangi in India. The bacteria of this disease are short, spherical rods measuring 0.5 x 0.6 to 1p and occur singly or in small chains. They are motile with peritrichous flagella and produce characteristic red or pink pigment.
Though a minor bacterial disease, the bacterium produces severe infection when inoculated into the worm. However, when taken orally, it produces varying degrees of infection depending upon the age of the larva. However, percentage mortality is higher during larval-pupal stage.

Causes of Flacherie Outbreak 
Unhygienic environment such as unhealthy mulberry leaves, succulant leaves in advanced ages, prolonged starvation of larvae, poor ventilation and high temperature are the main causes of flacheria outbreak. Furthermore, if mulberry plants are not exposed to good sunlight, mulberry leaves lack sufficient nutrients with the result larvae remain weak and become susceptible to disease. Thus, poor quality of mulberry leaves and malnutrition is the major reason of outbreak of disease. Some workers are of opinion that flacherie, like pebrine is transmitted from mother to progeny through eggs (Anonymous, 1971),

Management 
The preventive measures for all the bacterial diseases include thorough disinfection of rearing rooms, appliances and eggs, good ventilation, proper bed spacing, regular cleaning of the littre and maintenance of hygienic conditions. Since nutrition is considered to be a crucial factor, it must be ensured that worms are given proper quantity and good quality mulberry leaves exposed to sufficient sunlight. Rearing of disease free seeds is also helpful in checking the incidence of disease.