The immune response of Hermetia illucens larvae: preliminary evidence

The dipteran Hermetia illucens (Diptera: Stratiomyidae), also known as black soldier fly, is a promising insect species for waste management, thanks to the ability of the larvae to grow on a wide variety of organic substrates. Moreover, the high nutritional value of the larvae makes this insect useful for the production of feedstuff. Despite the great interest on this species, information about the biology of this insect remain scarce, especially about the immune system. In the present study we performed a preliminary investigation on the cellular and humoral response of H. illucens larvae. To this aim we conducted a morphological analysis of hemocytes that are involved in the cellular response. Moreover, we evaluated the main components of the humoral response after immune challenge with Gram-positive and Gram-negative bacteria. In particular, we analyzed phenoloxidase and lysozyme activity in the hemolymph of the larvae, and mRNA expression of antimicrobial peptides (AMPs) in the fat body. Our results show an increase of phenoloxidase and lysozyme activity in infected larvae compared to controls. Moreover, we observed a modification of AMP expression 6, 12, and 24h after the immune challenge compared to naive larvae. This study provides preliminary information on the immune system of H. illucens. This knowledge will hopefully open up the possibility to optimize the rearing procedures of H. illucens larvae and to obtain high quality larvae for feed production.