Effect of rosemary (Rosmarinus officinalis) supplement on the growth characteristics and larval metabolism of black soldier fly (Hermetia illucens L.)

Abstract

Abstract The black soldier fly (BSF), Hermetia illucens. L (Diptera: Stratiomyidae), is often harnessed to transform organic waste into nutrient-rich larval biomass, providing an alternative animal feed in the aquaculture industry. In Israel, rosemary (Rosmarinus officinalis) is a common ornamental plant in gardens that also demonstrates insecticidal and repellent properties and medicinal value. This study focuses on utilizing rosemary waste to produce nutrient-enriched BSF larvae for animal feed and potential medical applications. We evaluated BSF larval survivability, adult emergence and metabolomics following supplementation with different percentages of rosemary leaves (4%, 15%, and 20%, relative to 25 g of the total Gainesville diet). Surprisingly, we observed 95-99.6% larval survivability in the rosemary treatments, comparable to the control. Larval body weight slightly decreased by 4%, 12%, and 20%, respectively, measured as 219 ± 3 mg, 220 ± 3 mg, and 219 ± 4 mg, respectively, compared to the control (249 ± 5 mg) (x̄ ± SE; ). There was a significant difference in adult emergence at 10 days from larval addition (), but no difference after 16 days (). Metabolomics analysis unveiled the over-accumulation of metabolites in BSF larvae after rosemary supplementation linked to aminoacyl-tRNA biosynthesis, glutathione metabolism, phenylalanine metabolism, arginine biosynthesis, phenylalanine, tyrosine, and tryptophan biosynthesis, butanoate metabolism, and arginine and proline metabolism. Conversely, purine metabolism, tyrosine metabolism, and pantothenate and CoA biosynthesis were down-accumulated. Rosemary supplementation also led to the over-accumulation of antioxidant metabolites (rosmarinic acid, carnosic acid, and caffeic acid), suggesting that including rosemary powder in organic compost slightly reduced larval body weight but shortened adult developmental time and enhancing the nutritional value of BSF larvae. However, further molecular studies are necessary to understand BSF resistance and other biochemical changes resulting from rosemary inclusion in their diet.