Impact of Salmonella enteritidis Infection and Mechanical Stress on Antimicrobial Peptide Expression in Hermetia illucens

<i>Hermetia illucens</i>, the black soldier fly, is a common and widespread fly of the family <i>Stratiomyidae</i>. Its ability to grow on contaminated substrates suggests the production of antimicrobial peptides that enable its survival. This study aimed to verify the impact of direct and indirect infection with <i>Salmonella enteritidis</i> on the expression of defensins and cecropins in <i>Hermetia illucens</i> larvae. In addition to an infection with a microorganism, it was interesting to verify if the expression of peptides and the relative action of hemolymph changed in larvae subjected to mechanical stress by abdominal puncture. The peptide fraction of the hemolymph of infected larvae was tested using antibiogram and minimum inhibitory concentration tests against <i>Salmonella enteritidis</i> and <i>Salmonella typhimurium</i>. Both molecular and microbiological tests were carried out at three different time points, on larvae not subjected to any treatment (T-0), four hours after treatment (T-1), and 24 h after treatment (T-2). The results of the microbiological tests showed the antimicrobial action of the peptide fraction of the hemolymph against both <i>S. typhimurium</i> and <i>S. enteritidis</i>; for the latter one, the action was more marked. Interesting results were also found for larvae subjected only to mechanical stress by puncture. Molecular tests on the expression of defensins and cecropins were in full agreement with those obtained in the microbiological tests, with expression more pronounced in larvae infected directly with <i>Salmonella enteritidis</i>. Temporal and condition-specific regulation of defensins and cecropins highlights the complexity of the immune response and suggests sophisticated mechanisms by which the host fine-tunes antimicrobial peptide expression to enhance pathogen defense while preventing excessive immune activation.