Morphofunctional characterization of hemocytes in black soldier fly larvae

Abstract

In insects, the cell-mediated immune response involves an active role of hemocytes in phagocytosis, nodulation, and encapsulation. Although these processes have been well documented in multiple species belonging to different insect orders, information concerning the immune response, particularly the hemocyte types and their specific function in the black soldier fly Hermetia illucens, is still limited. This is a serious gap in knowledge given the high economic relevance of H. illucens larvae in waste management strategies and considering that the saprophagous feeding habits of this dipteran species have likely shaped its immune system to efficiently respond to infections. The present study represents the first detailed characterization of black soldier fly hemocytes and provides new insights into the cell-mediated immune response of this insect. In particular, in addition to prohemocytes, we identified five hemocyte types that mount the immune response in the larva, and analyzed their behavior, role, and morphofunctional changes in response to bacterial infection and injection of chromatographic beads. Our results demonstrate that the circulating phagocytes in black soldier fly larvae are plasmatocytes. These cells also take part in nodulation and encapsulation with granulocytes and lamellocyte-like cells, developing a starting core for nodule/capsule formation to remove/encapsulate large bacterial aggregates/pathogens from the hemolymph, respectively. These processes are supported by the release of melanin precursors from crystal cells and likely by mobilizing nutrient reserves in newly circulating adipohemocytes, which could thus trophically support other hemocytes during the immune response. Finally, the regulation of the cell-mediated immune response by eicosanoids was investigated.

Black soldier fly larvae should be considered beyond their use as feedstuff

“…These include various families of AMPs, low molecular weight peptides with potent microbicidal efficacy against bacteria, viruses, and fungi, as well as lysozymes, both contributing to the insect immune response. BSF larvae exhibit a sophisticated immune system likely shaped by their life strategies, as they live on decaying substrates which can bring them into contact with pathogens (Bruno et al, 2021;Bruno et al, 2023). So, it is not surprising that dozens of AMPs that are reactive to bacterial challenge have been identified in BSF through large-scale transcriptomic and proteomic screenings (Moretta et al, 2020;.…”

Editorial: Insect behavioral adaptations and immune responses to stress

“…This means that although insect behaviors are innate, they can be environmentally and physiologically adapted. Similarly, the insect immune response to infection differs according to the type of pathogen and infection route, the type of host and the presence of microbiota and its microbial composition ( Westwick and Rittschof, 2021 ; Bruno et al, 2022 ; Eleftherianos et al, 2022 ). Finally, we would like to thank all the authors, reviewers, and editors for their contributions to this article Research Topic.…”