Effects of feed and probiotic bacteria on Tenebrio molitor performance and entomopathogen susceptibility

Abstract

Lactobacillus plantarum is available in several probiotic products due to its proven abilities in reducing inflammatory bowel disease, the irritable bowel syndrome and preventing diarrhea.Application to Diptera and Lepidoptera showed effects of Lb. plantarum on host development and performance raising questions about application to other insect Orders. Research objectives and outline of this thesisThe purpose of this thesis is to provide a broad overview of T. molitor symbionts, conduct experimental studies focused on potential application of beneficial symbionts such as Pediococcus pentosaceus KVL B19-01 and Lactobacillus plantarum WJB as potential probiotic strains for decreasing the risk of infections in mass-rearing conditions and for optimizing the quality of the chemical composition of the larvae as they may be consumed as feed and food, representing one of the solutions for upscaling the value of by-products along the food chain.Chapter 2 provides a review of the potential of probiotic applications in mass-reared insects. Methods of isolation, identification and production of probiotic bacterial species are provided, taking into consideration methods of their application in an insect mass-rearing context and the important connections between host-microbiota and provided feed in health preservation and disease management.Chapter 3, provides a review addressing the richness and the variety of interactions between the yellow mealworm and its symbionts, methods of pathogen detection and insights for reducing the risk of pathogen infection in rearing facilities.Chapter 4, is an experimental study focused on T. molitor susceptibility to the entomopathogen Bacillus thuringiensis sv. morrisoni biovar tenebrionis (4AA1) (Btt) in conditions resembling the mass-rearing system environment. The study highlights the direct correlation between entomopathogen load and the yellow mealworm larval growth and mortality. Larvae having higher body mass showed to be more resistant to the pathogen and were not compromised in feed conversion. The data also showed that Btt can persist in the tested conditions suggesting a certain risk for the rearing.Chapter 5, focus on the effects of diet composition and two potential probiotic strains, Pediococcus pentosaceus KVL B19-01 and Lactobacillus plantarum WJB, on performance and microbial community composition of T. molitor larvae affected by the entomopathogens Metarhizium brunneum KVL 12-30 and Bacillus thuringiensis sv. morrisoni biovar tenebrionis (4AA1) single or co-infection.The larvae presented increased growth and survival in case of co-infection when fed with diet supplemented with P. pentosaceus. The bacterial community composition of the larvae was similar in all treatments, indicating that the probiotic strain did not establish at a detectable level in the insect, however, its transient presence improved larval performance in its early developmental stages.In Chapter 6, the effects of diet composition and probiotic provision on T. molitor larval performance and chemical com...