Black larvae in lepidopterous often are the sign of viral infections. In similar cases we owed to destroy all vials with black larvae and to sterilize all instruments.

I guess Galina is right. However, in case you'd like to exclude bacterial infections, try spraying your cabbage leaves with an Aureomycin suspension/solution (depending on the formulation).

Good luck, Michael

In case of viral infection, the infected host body becomes flaccid and its skin (integument) ruptures easily.

Discoloration of larvae in bacterial and viral diseases usually be observed. But in Baculovirus the skin of larvae has torn and black liquid is removed from the body. But in bacterial infections especially in Bacillus thuringiensis usually stiff body and the like are burned and Coal. The microscopic observation of the larvae body contents is useful.

Discoloration of larvae in bacterial and viral diseases usually be observed. But in Baculovirus the skin of larvae has torn and black liquid is removed from the body. But in bacterial infections especially in Bacillus thuringiensis usually stiff body and the like are burned and Coal. The microscopic observation of the larvae body contents is useful.

I think it is granulosis virus (GV) infection, Since larvae symptom are not completely black and is almost greenish black. We also had similar problem in our culture. Hence, clean the rearing boxes with 10% Sodium hypochloride solution to avoid the spread and it will be rectified.

Dear Sir,

In 2008, I have been rearing  Plutella xylostella in my laboratory. I hope this information will help you. It's very important clean all of instrument including larvae food.

What their food?cabbage leaves or another brassicaceae? you must washing them in flow water and drying for 10-15 minutes in temperature room. Then, you must clean everyday your larvae boxes from food remains and faeces. After cleaning, please washing and sterilize your small laboratory tools with alcohol 70%. This methods will avoid bacterial or microorganism contamination. Good luck !!!

Hi Gireesh:

To keep your Plutella xylostella rearing containers free of viral or bacterial diseases you must  clean your cage with a 10 % sodium hypochlorite solution. Also you can wash the cabbage leaves with this solution.  Avoid sealed containers with high humidity. Keep your colony in mesh cages on sites with controlled humidity and get your stock breeding colony free of virus to avoid contamination and death of the larvae.

Regards,

Luis Miguel

You, you should all of the tools and leaves surface for insect rearing previously sterilized in 0.5% sodium hypochlorite solution for 10 min and washed three times in sterile, distilled water.

Thanks all for your reply and suggestions. We are suspecting it as a viral disease, however, there is no fluid oozing out of the body. Larvae are becoming blackish, dry and die. We have almost controlled its spread using sodium hypochlorite as well as autoclaving the brushes etc. used in rearing the DBM.

With regards,

Gireesh

You can also sterilize your lab by using UV tube light overnight, but do shift everything to other place first.

For disease free rearing of DBM you can treat the food with 100 ppm streptocycline