Agricultural by-products as functional substrates modulate the growth, the cytoprotective mechanisms and the antioxidant potential of Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract The emergence of insects as a nutrient source in the human diet and animal feed propels the urgent development of a viable mass production sector. The objective of the present study was to evaluate the suitability of rice and corn by-products as substrates for mealworm rearing namely Tenebrio molitor L. (Coleoptera: Tenebrionidae) in terms of growth, stress response, and antioxidant defence. In this context, mealworm larvae were reared on wheat bran (WB) as the control substrate, rice bran (RB) and corncob (CC), both enriched with post-distillation residues of Mediterranean medicinal-aromatic plants (MMAPs; 0, 10 or 20% w/w). Cell signaling components including Heat shock proteins (Hsps), Mitogen-activated protein kinases (MAPKs), and apoptotic proteins (Bax and Bcl-2) were assessed through immunoblot analysis, while the spectrophotometric technique was employed to determine the activities of the antioxidant enzymes (superoxide dismutase, catalase, and glutathione reductase). Regardless of the MMAPs supplementation level, a weight reduction was apparent in larvae reared on RB substrate, while 20% MMAPs supplementation in WB substrate seemed to trigger an apoptosis-associated weight loss as demonstrated by the elevated Bax/Bcl-2 ratio. In contrast, corncob was regarded as a nutritionally adequate substrate considering that the efficient larvae growth was accompanied by suppression of Hsps expression and MAPKs activation. The elevated antioxidant activity in T. molitor of the 10% MMAPs-enriched RB and CC substrates may underline the attention that must be given in the utilization of MMAPs in insects’ production processes due to the potential insecticidal and repellent effects. Collectively, the effective valorization of agricultural-by-products and MMAPs supplementation in T. molitor feed varies depending on the source of the substrate and the potential interactions among the bioactive compounds.