Unveiling the protein puzzle: How does protein in the feeding substrate affect Zophobas morio larval growth and performance?

Abstract During the last decade, mini-livestock has gained much attention as alternative nutrient sources for food and feed applications. The optimal feeding substrate for many edible insect species has been thoroughly studied. However, the biology of Zophobas morio (F.) (Coleoptera: Tenebrionidae) has not been fully investigated, resulting in a gap in its feeding preferences. Based on the above, the aim of this study was to evaluate the protein content impact, in terms of quantity and quality, in the feeding substrate of Z. morio larvae. Thus, in the first bioassay Z. morio larvae were reared on diets consisting of wheat bran and yeast with different protein percentages (i.e., 15.2%, 20%, 22.5%, 25%, 27.5%, and 30%). As a follow-up to the first bioassay, in the second bioassay isoproteinic diets consisting of different protein sources (i.e., soy, egg white, pea, and brown rice) were formulated. For both bioassays, larval survival and weight were recorded every two weeks while at the end of the bioassays the larval development time, FCR, ECI, ECD, and SGR were calculated. Based on the results, optimal larval growth and performance were recorded in the treatment with a diet consisting of 20% protein. Concerning the different protein sources, larval growth was not supported by pea protein isolate, while the highest larval growth was recorded for the treatment with soy protein isolate. As Z. morio appears to be a well-promising insect-based protein source, the results of this study contribute to the optimization of its rearing.