Much of the information for the pathology of lepidopterans is derived from the silkmoth industry (Bombyx mori) and many of the diseases are still referred to by their French names. It is important to remember that these terms are not technical / scientific terms and were in use long before the the disease-causing organisms were even known or identified.
The disease I refer to --- known as 'flacherie'--can be caused by both viruses and bacteria and, in some cases, a combination of the two. Generally, in most insect diseases, when progressed disease is accompanied by a foul odor it is assumed to be bacterial. If the infection is without a foul smell, it is assumed to be caused by other organisms. But this may not always be entirely accurate.
The main causative pathogens are Streptococcus sp., Staphylococcus sp., Bacillus thuringiensis and Serratia marcescens and non-occluded viruses such as infectious flacherie virus (BmIFV) and densonucleosis virus (BmDNV). Flacherie can also be caused by the combined infection of bacteria and viruses.
✔The larvae become soft and flaccid
✔The growth of affected larvae is retarded
✔larvae become inactive and vomit gut juice
✔feces becomes soft with high moisture content (sometimes larvae produce chains of fecal pellets )
✔ rectal protrusion is often observed
✔the larva's cephalothoracic region becomes translucent
Here is a link to a PDF of this information:
The source of infection? Many of these organisms are present in the environment in huge numbers. In the case of Staphylococcus and Streptococcus-- they are even present in the human throat and sinuses! Viruses are a different story, but can be abundant on leaves when insectivorous birds defecate on plants.
In any case, the best solution is prevention. You've heard this all before...an epidemic of these diseases can be prevented or arrested by rigid hygiene, control of free water in the rearing chambers, proper hosts that are fresh, low humidity, a method to keep feces from contact with larvae, proper temperatures, prompt removal of sick or dead individuals, low density rearing rather than crowded conditions, and start with healthy stock, if possible.
That said, you will need to clean and disinfect EVERYTHING that comes into contact with sick insects if you intend to use any of these materials in the future for rearing insects. It may be more efficient in some cases to discard materials and start with new cages, boxes, etc rather than spend time disinfecting them.