Influence of Feed Form on Tenebrio molitor L. Adults and Young Larvae Performance

Competitive industrial farming of Tenebrio molitor L. requires strategies aimed at reducing production costs and improving overall efficiency. Among variable costs, feed is one of the most significant components. Previous research has mainly focused on the nutritional composition of diets, the use of agri-food by-products, and the optimization of multicomponent formulations, sometimes administered in pelleted form during bioassays. However, knowledge about the influence of the administration form is scarce. This study investigated the effects of different feed forms—finely ground (<0.5 mm), coarsely ground (0.5–2 mm), and assembled (pellets, cookies, and crumbles)—on both adult and larval performance. Three feeds (wheat bran, brewer’s spent grain, and chicken feed) were tested to assess adult productivity and larval growth. The results showed non-significant differences in adult survival between feed forms, whereas finely ground feed significantly increased adult productivity and the survival of newborn larvae. Furthermore, larvae in the growing phase (40–60 days old) were able to effectively utilize assembled feeds, with no significant differences in larval weight compared to those reared on ground diets. These findings suggest that pelleted formulations for T. molitor farming should include a fraction of finely ground material to support early larval stages, thereby optimizing survival and development. Moreover, the different influence of feed form provides useful information for planning evaluation trials of multicomponent assembled diets.