Effect of Probiotics on Tenebrio molitor Larval Development and Resistance against the Fungal Pathogen Metarhizium brunneum

Abstract

In recent years, the yellow mealworm (Tenebrio molitor L.) has demonstrated its potential as a mass-produced edible insect for food and feed. However, challenges brought on by pathogens in intensive production systems are unavoidable and require the development of new solutions. One potential solution is the supplementation of probiotics in the insect’s diet to obtain the double benefits of improved growth and enhanced immune response. The aim of this study was to evaluate the effects of diet-based probiotic supplementation on T. molitor larval survival, growth, and resistance against a fungal pathogen. Three probiotic strains, namely Pediococcus pentosacceus KVL-B19-01 isolated from T. molitor and two commercialized strains for traditional livestock, Enterococcus faecium 669 and Bacillus subtilis 597, were tested. Additionally, when larvae were 9 weeks old, a pathogen challenge experiment was conducted with the fungus Metarhizium brunneum. Results showed that both P. pentosaceus and E. faecium improved larval growth and larval survival following fungal exposure compared to the non-supplemented control diet. Since B. subtilis did not improve larval performance in terms of either development or protection against M. brunneum, this study suggests the need for further research and evaluation of probiotic strains and their modes of action when considered as a supplement in T. molitor‘s diet.

Minor impact of probiotic bacteria and egg white on Tenebrio molitor growth, microbial composition, and pathogen infection

“…However, live P. pentosaceus increased larval survival following challenge by a pathogen, as observed by Dahal et al. ( 45 ). The mechanisms behind the observed results are not yet fully understood, especially in the case of the deactivated P. pentosaceus cells.…”

“…The mechanisms related to pediocin production in the gut environment of the yellow mealworm still need to be investigated, taking into consideration the gut pH ( 67 ) and the mass-rearing environmental conditions that might affect the insect microbiota dynamics ( 68 ). Further studies should also consider the impact of the probiotics on the whole life cycle of T. molitor , as earlier reported ( 25 , 45 ). Moreover, the study of the persistence of pathogens and probiotics in the larvae was possible due to the controlled experimental conditions, characterized by the timed provision of feed and removal of frass ( Figure 2 ).…”

“…Furthermore, an increased larval performance may not be directly due to the probiotic acting as a nutrient source; rather, the mechanism could be the direct interaction of P. pentosaceus KVL B19-01 with larval immunological or physiological mechanisms, leading to increased growth and immune resistance to pathogens ( 64 ). The ability of P. pentosaceus to produce and excrete antimicrobial secondary metabolites such as pediocins ( 65 , 66 ) might play an important role in shaping the insect microbiota dynamics by favoring probiotic gut colonization and avoiding pathogen proliferation ( 45 ). The mechanisms related to pediocin production in the gut environment of the yellow mealworm still need to be investigated, taking into consideration the gut pH ( 67 ) and the mass-rearing environmental conditions that might affect the insect microbiota dynamics ( 68 ).…”

Recent trends in insect gut immunity

“…These strains contribute as gut microbiota and promote host growth and development. Moreover, they protect against entomopathogenic fungi, such as Metarhizium brunneum ( 87 ). P. pentosaceus significantly protects T. molitor from six different insect pathogenic strains, including B. thuringiensis and species of Serratia and Pseudomonas bacteria ( 88 ).…”

Validation of Diets with Tomato Pomace in Complete Cycle Breeding of Tenebrio molitor (L.) (Coleoptera: Tenebrionidae)

“…Diets can influence mealworms' immune responses to the entomopathogenic fungi, Beauveria bassiana, by increasing gene expression of the antimicrobial peptide, Tenecin 3 [19]. Diets supplemented with the probiotic strains, Pediococcus pentosacceus KVL-B19-01 and Enterococcus faecium 669, improved Metarhizium brunneum-infected growth and larval survival [20].…”