Do antimicrobial peptide levels alter performance of insect-based aquaculture feeds - a study using genetic models of insect immune activation

Insect meals are an increasingly common ingredient in pet food and animal feeds. Some studies have reported increased resistance to disease in animals fed insect-based diets, but the mechanisms of this effect have only rarely been investigated. We hypothesised that antimicrobial peptides (AMPs) naturally present in insects contribute to disease resistance. AMPs are part of the insect immune response, and as such their levels differ dramatically depending on the state of immune activation. In this study, transgenic fruit flies (Drosophila melanogaster) lines were used to generate insect-based feeds with high and low AMP levels. Juvenile rainbow trout (Oncorhynchus mykiss) were fed these insect diets and challenged by immersion with Yersinia ruckeri to assess changes in disease resistance. Survival rates of fish fed the high AMP insect diet were not significantly different from those fed the low AMP insect diet, though there were trends towards higher survival and lower Y. ruckeri load in the intestines of fish fed the high AMP diet. The fish intestinal microbiomes were studied in challenged and mock-challenged fish. In mock-challenged fish, no differences were apparent between the microbiomes of each diet group. In Y. ruckeri challenged fish, however, the intestinal microbial communities differed between fish fed the low and high AMP diets at each time point after infection. Overall, despite its limitations, this study offers a prospective view of how to leverage the genetic tools and experimental approaches present in the Drosophila community for research in commonly farmed insects (e.g. Hermetia illucens and Tenebrio molitor).