**Anna Bordiean , Michał Krzy ˙zaniak \*, Mariusz J. Stolarski and Dumitru Peni**

Department of Plant Breeding and Seed Production, Faculty of Environmental Management and Agriculture, University of Warmia and Mazury in Olsztyn, Plac Łódzki 3, 10-724 Olsztyn, Poland; anna.bordiean@uwm.edu.pl (A.B.); mariusz.stolarski@uwm.edu.pl (M.J.S.); dumitru.peni@uwm.edu.pl (D.P.) **\*** Correspondence: michal.krzyzaniak@uwm.edu.pl

Received: 9 November 2020; Accepted: 1 December 2020; Published: 3 December 2020

**Abstract:** Since the world's population will continue to grow in the next decades, the problem of providing people with food will deepen. One-third of the food production volume is wasted while nearly one in ten people in the world suffer from hunger. To reduce the negative impact of human activity on the environment and meet the needs of the population, alternative sources of protein are proposed. Yellow mealworm larvae can be used as a source of food and animal feed. Therefore, this study aimed to compare the growth performance, feed conversion ratio (FCR) and efficiency of ingested feed (ECI) by yellow mealworm larvae fed 13 different diets containing chicken feed (CF), rapeseed meal (RM), wheat bran (WB) and willowleaf sunflower (WS) residues after the process of supercritical CO2 extraction. The mean dry individual bodyweight for all diets used in the experiment was 31.44 mg dry matter (d.m.) Mealworms fed diet mixes that contained WB demonstrated the highest dry individual larval weight (from 40.9 to 47.9 mg d.m.). A significantly lower dry individual larval weight was found for mealworms fed solely WS residues (3.9 mg d.m.). The FCR ranged from 1.57 to 2.08, for pure CF and pure WS diet, respectively. The ECI of yellow mealworm larvae varied significantly (mean value 20.1%) and depended on the diet. Moreover, the ECI of mealworm was significantly the lowest and amounted to 5.9% for the pure WS diet. The industrial residues investigated in this study can be successfully used for mealworm farming, excluding pure willowleaf sunflower residues.

**Keywords:** *Tenebrio molitor*; edible insects; larval development; feed conversion ratio; agricultural and industrial residues; lignocellulosic biomass; bioconversion
