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Growth performance and feed conversion of Ruspolia differens on plant‐based by‐product diets

The use of food industry by‐products in insect feeds has gained increasing attention recently. However, the understanding of how well the economically valuable edible insect Ruspolia differens (Serville) (Orthoptera: Tettigoniidae) can grow and develop with plant‐based by‐product feeds is currently lacking. It is important to determine the nutritional requirements, especially protein demand, of this species before developing artificial feeds for mass‐rearing. We reared R. differens with four control diets and 12 plant‐based by‐product diets in which the major protein source came from food industry by‐products, including potato‐protein, barley mash, barley feed, turnip rape, a mix of broad bean and pea, and a mix of potato, carrot, and apple. We asked whether the performance (development time, survival, and weight), feed conversion, and fatty acid composition and content differed among diet treatments. Furthermore, the 12 experimental by‐product diets were designed to reach six protein levels. We found that R. differens can be reared with various by‐product diets, but development time, survival, and weight differed among diets. Barley feed, barley mash, and potato protein diets seem to be good options for rearing, and potato glycoalkaloids do not affect the performance of R. differens. Individuals fed on the various by‐product diets also differed in their fatty acid composition and content. Increasing protein levels in diet up to 17% enhanced growth, development time, and survival, but no further enhancements were seen when fed diets with protein levels higher than this. The high protein levels decreased feed conversion rate. Our results can be valuable for designing feeds for insect mass‐rearing technology. The use of food industry by‐products in the diets for R. differens could increase the re‐use of local resources and enhance circular economy.