Melanization and antimicrobial peptides (AMP) generation are two defense pathways of insect immune system.Melanization is dependent on Prophenoloxidase (PPO) activation, and AMP genes transcription is carried out through NF-kB pathway.Generally, Gram-negative bacteria infection induces AMP expression by IMD pathway; while Gram-positive bacteria and fungi infection induce AMP expression by Toll pathway.