The melanization is a response against hemolymph injury of insects. The clotting response against injuries is very fast and culminates with melanization as a defense form of insect against hemolymph disrupt.
We challenge the immune system with bacteria and pricking the larvae then leave them to feed again for one day. Upon extracting the hemolymph for experimental application it will start to turn brown almost immediately. In larvae that were not immune challenged, but pricked with a sterile needle we observed that the hemolymph turned brown only after 24hrs.