Diseases and Problems

Experiencing Problems? Have some of your silkworms died? or are they looking a little sick? Please read

below to find out the cause.

 

The number 1 most important rule in rearing Silkworms is Hygiene!

 

This means personal Hygiene, washing hands with soap and drying your hands completely on a clean dry paper or

cloth towel BEFORE handling silkworms.

 

It also means keeping the breeding container for your silkworms CLEAN.

 

If using cardboard boxes it is important to obtain boxes that are clean and dry without contamination of any type. 

The boxes can be lined with clean paper towel which gives an added sterile layer between the worms and the

cardboard and also helps to absorb moisture.

 

If using plastic tubs or glass terrariums it is important that they are cleaned thoroughly with soap and water and

dried completely before the silkworms are placed in them (Silkworm industries always use bleach).  Again paper towel

can assist to keep the worms moisture free. It also assists in removing the leftover mulberry and frass when cleaning.

 

Common Problems

 

Eggs do not hatch

 

Overheating

 

Such as exposure to heat from lamps or sunlight in which case eggs will go a reddish colour appearing flat rather than

rounded and plump (small indents in the top of eggs that are a normal grey blue colour are not a problem).

 

Exposure to condensation or water

 

In which case eggs will go a darker grey blue colour and will swell to larger than normal size – eggs will not hatch.

 

This may occur from high levels of humidity in the breeding container resulting in condensation and pooling of water.

  Ensure ventilation of breeding container minimum twice daily. If using a damp piece of towel in breeding container to

increase the humidity ensure eggs do not contact the damp cloth.

 

If eggs become wet accidentally and are quickly dried they will still hatch.  Pat dry with paper towel with very light

pressure to prevent bursting of eggs.

 

Exposure to pressure

 

In which case eggs will burst and appear flattened, the fluid from within the eggs will be visible – eggs will not hatch.

 

Cold temperature in breeding area

 

Temperature below 26 degrees c can cause eggs to stay unhatched for a longer than usual period.

 

Solutions:

 

Ensure a daylight photoperiod of 12L:12D (as in equal length of day and night).

 

Increase ambient room temperature without exposing the eggs to any direct heat from lamps or sunlight.

 

Hatchlings shrivel and die.

 

In this case it is very simple, your silkworms have not had enough to eat and have died.  There is no disease present

in Australia that kills silkworm hatch-lings, so malnourishment is the main cause of hatch-ling death other than ant

attack. Other causes are excessive moisture or heat.

 

Hatchlings disappear.

 

This is usually the result of ant attack, particularly if you are in WA, NT or QLD.  Other insects may also take your

hatchlings.  Use a water bath to prevent this.  To use a water bath fill a large plastic tub or tray with water, place the

breeding container on top of a brick or upturned pot that is placed in the water bath.  Ensure worms cannot fall into the

water bath and drown.

 

Silkworms writhe/flip back and forth and vomit gut juice.

 

This is caused by INSECTICIDE on mulberry leaves. It is a very sad way for silkworms to die.  If you are unable to

ascertain whether a mulberry tree has or has not been sprayed please batch test the leaves with only a few silkworms

first.  If the leaves are sprayed the silkworms will show symptoms within 6 – 12 hours of eating the leaves depending

on the potency of the insecticide residue on the leaves.

 

 

 

Diseases

 

Fortunately the worst of the silkworm diseases are not present in Australia.  It is for this reason that importing

silkworm eggs is restricted.

 

Disease can be circumvented by strict hygiene and quality mulberry feed either with quality fresh leaf or chow.  Strict

hygiene is also necessary when preparing and feeding silkworms with chow.

 

1.

 

Problem: Worms appear lethargic and flaccid, growth is stunted. The cephalothoracic region may be translucent.

Worms vomit gut juice (green to brown yellow), develop dysentery and excrete chain type fecus. Dead worms putrefy

quickly often with a foul odor. The colour of dead worms is black/brown, if you try to lift a dead worm it will break

open.  Dead worms break open when healthy worms walk over them covering the healthy worms in fluid.

 

Name and Cause: Flacherie: Bacteria and viruses cause the disease individually or in combination. Flacherie is most

often caused by high humidity and fluctuating temperatures.  Flacherie is also caused by mould, fermentation and

humidity build up in waste mulberry and frass. It is most often seen in the 4th and 5th instars but can occur in the

earlier instars. If your silkworms get infected during the 3rd , 4th or early 5th instar, symptoms of the disease will be

observed prior to spinning or pre-pupal stage.   If the infection is in the late 5th instar, the mortality will be in the pupal

stage in which case your cocoons will not hatch, this is most often identified by your cocoons emitting a foul smell.

Changing from coarse Mulberry to tender Mulberry leaf favours the disease development especially if the change is

made abruptly after feeding coarse leaves for sufficiently long time.

 

Solution: As Flacherie is most often contracted in the early Instars and does not present until the later instars it is

usually impossible to eradicate without destroying the entire colony. You may remove the sick or dead silkworms and

any silkworms that have contacted fluid.  Wash hands carefully before handling healthy worms.  Dispose of dead or

sick worms by either burying 2 feet or more underground, double bagging and placing in the outside rubbish bin or by

burning.

 

If you choose to destroy the whole colony place all worms in a bag and place into the freezer.

 

Before raising any more silkworms ensure your breeding area, plastic tubs and terrariums have been cleaned with

bleach.  It is best to wait 3 months before rearing more silkworms.

 

 

 

2.

 

Problem:  Silkworms are sluggish with swollen intersegmental region, The integument of diseased larvae are fragile

and breaks easily, a milky fluid oozes out from the larval body, the diseased larvae do not settle for moult and show

shining integument, the larvae appear to be restless, the dead larvae hang by hind legs head downward. Basically if

your worms will not spin and just die, this is the cause. In silkworms infected with a high dose of virus, the ecdysone

hormone required for moulting and maturation will be destroyed. The larval period will be simply continued indefinitely

due to lack of ecdysone till the larvae develop the disease. This  is why we see the disease associated with worms

that fail to moult and spin their cocoon.  If the infection level is low, larva pupate will die in pre-pupal or pupal stage.

 

Name and Cause: Grasserie: The Grasserie disease is caused by a virus – Nuclear polydedrosis. Grasserie is similar

to Flacherie in that poor hygiene and poor Mulberry Quality contribute as well as humidity and temperature

fluctuations.  Avoid high ( 28-35C), low rearing temperature ( 10-20 C) and rearing humidity ( <70%). As for Flacherie.

 

 

Solution:  As for Flacherie.

 

 

3.

 

Problem: The diseased silkworms prior to death will be lethargic and on death are flaccid, oil specks may be seen on

the surface of silkworms, they gradually become hard, dry and mummify into a white or green coloured structure.

(please see image) The diseased pupae will be hard, lighter and mummified.

 

Name and Cause: White Muscadine is caused by a fungus Beauveria Bassiana and the Green Muscadine is caused

by a fungus Spicaria Prasina.  Aspergillosis is common in young age Silkworms and the infected larvae will die. Dark

green       ( Aspergillus Flavus) or rusty brown ( Aspergillus Tamari) Mycelial cluster are seen on the dead silkworm

body. Caused by the fungus being present on the mulberry leaf transported there by other insects.

 

Solution: Hygiene. Prevent Humidity build up. Keep mulberry tree’s free of insects (without the use of insecticides as

this will kill your silkworms). Muscardine is common in winter and rainy seasons because these seasons provide

favourable environments for infection, growth and multiplication of the pathogen.

 

This type of dead Silkworm is the source of the traditional Chinese Medicine “bombyx batryticatus” or “stiff silkworm”.

It is the dried body of the 4~5th stage larva of silkworm died of the white muscadine disease which is caused by the

infection of the Beauveria bassiana . Its uses are to dispel wind, dissolve phlegm and relieve spasm!