The black soldier fly (BSF; Hermetia illucens L.) is a very promising insect species due tothe ability to convert low-value substrates in highly nutrient feed. This work aimed to study theeffect of three nominally isoenergetic diets containing plant ingredients such as barley, alfalfa, andwheat byproducts, formulated to be higher in nonfiber carbohydrates (TMD1), fibers (TMD2), andprotein (TMD3) in comparison to an extensively genetic modified cereal (cornmeal)-based diet (C),on the growth, yield, and nutritive traits of BSF prepupae (BSFPs). Three growing trials with fourbiological replicates were carried out. Proximate and fatty acid analyses were performed on the dietsand BSFPs. Feed conversion ratios (FCR), dry matter and nutrient yields, and apparent concentrationfactors (aBCF) for fatty acids (FAs) were calculated. Diet formulation had a substantial effect on thesurvival, development rate, and larval yield, but the FCR was unaffected. The BSFPs fed TMD3did not result in a higher crude protein content in comparison to the C or TMD2 diets. Despite theleveled fat content of the diets, BSFPs reared on TMD1 were highest in fat, saturated FA, and fatyield. An apparent bioconcentration factor (aBCF) value lower than unity that was found for theunsaturated FA suggests that the BSFPs inefficiently absorb them from the diet or possibly turn theminto saturated FA. However, the unsaturated FA accumulation in BSFPs depended on the levels thatwere found in the diet, which suggested some possibilities for the FA profile modulation. Overall, theTMD2 performed well despite the low-value of its main ingredients and high fiber content and can beconsidered to be a feasible option for the mass rearing of BSFPs that are intended for animal feed.