Characterisation and mode of action analysis of black soldier fly (Hermetia illucens) larva derived haemocytes.

With the growing importance of the black soldier fly (Hermetia illucens) for both sustainable food production and waste management as well as for science, a great demand of understanding its immune system arises. Here, we present the first description of the circulating larval haemocytes with special emphasis on uptake of microorganisms and distinguishing haemocyte types. With histological, zymographic, and cytometric methods and with a set of haemocyte binding lectins and antibodies, the haemocytes of H. illucens are identified as plasmatocytes, crystal cells, and putative prohaemocytes. Total haemocyte counts (THC) are determined, and methods for THC determination are compared. Approximately 1100 haemocytes per microlitre haemolymph are present in naive animals, while haemocyte density decreases dramatically shortly after wounding, indicating a role of haemocytes in response to wounding (and immune response in general). The determination of the relative abundance of each haemocyte type (differential haemocyte count, DHC) revealed that plasmatocytes are highly abundant, whereas prohaemocytes and crystal cells make up only a small percentage of the circulating cells. Plasmatocytes are not only the most abundant but also the professional phagocytes in H. illucens. They rapidly engulf and take up bacteria both in vivo and in vitro, indicating a very potent cellular defence against invading pathogens. Larger bioparticles such as yeasts are also removed from circulation by phagocytosis, but slower than bacteria. This is the first analysis of the potent cellular immune response in the black soldier fly, and a first tool box that helps to identify haemocyte (types) is presented. This article is protected by copyright. All rights reserved.