Amelioration of growth, nutritional value, and microbial load of Tenebrio molitor (Coleoptera: Tenebrionidae) through probiotic supplemented feed

Lactobacillus melliventris promotes hive productivity and immune functionality in Bombus terrestris performance in the greenhouse

Bumblebees are important pollinators in agricultural ecosystems, but their abundance is declining globally. There is an urgent need to protect bumblebee health and their pollination services. Bumblebees possess specialized gut microbiota with potential to be used as probiotics to help defend at-risk bumblebee populations. However, evidence for probiotic benefits on bumblebees is lacking. Here, we evaluated how supplementation with Lactobacillus melliventris isolated from bumblebee gut affected the colony development of Bombus terrestris. This native strain colonized robustly and persisted long-term in bumblebees, leading to a significantly higher quality of offspring. Subsequently, the tyrosine pathway was upregulated in the brain and fat body, while the Wnt and mTOR pathways of the gut were downregulated. Notably, the field experiment in the greenhouse revealed the supplementation of L. melliventris led to a 2.5-fold increase in the bumblebee survival rate and a more than 10% increase in the number of flowers visited, indicating a better health condition and pollination ability in field conditions. Our study represents a first screening for the potential use of the native gut member, L. melliventris, as probiotic strains in hive supplement for bumblebee breeding, which may be a practical approach to improve immunity and hive health.

Hemolymph metabolism of black soldier fly (Diptera: Stratiomyidae), response to different supplemental fungi

The black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), is commonly used for organic waste recycling and animal feed production. However, the often inadequate nutrients in organic waste necessitate nutritional enhancement of black soldier fly larvae, e.g., by fungal supplementation of its diet. We investigated the amino acid composition of two fungi, Candida tropicalis (Castell.) Berkhout (Saccharomycetales: Saccharomycetaceae) and Pichia kudriavzevii Boidin, Pignal & Besson (Saccharomycetales: Pichiaceae), from the black soldier fly gut, and commercial baker's yeast, Saccharomyces cerevisiae Meyen ex E.C. Hansen (Saccharomycetales: Saccharomycetaceae), and their effects on larval growth and hemolymph metabolites in fifth-instar black soldier fly larvae. Liquid chromatography-mass spectrometry was used to study the effect of fungal metabolites on black soldier fly larval metabolism. Amino acid analysis revealed significant variation among the fungi. Fungal supplementation led to increased larval body mass and differential metabolite accumulation. The three fungal species caused distinct metabolic changes, with each over-accumulating and down-accumulating various metabolites. We identified significant alteration of histidine metabolism, aminoacyl-tRNA biosynthesis, and glycerophospholipid metabolism in BSF larvae treated with C. tropicalis. Treatment with P. kudriavzevii affected histidine metabolism and citrate cycle metabolites, while both P. kudriavzevii and S. cerevisiae treatments impacted tyrosine metabolism. Treatment with S. cerevisiae resulted in down-accumulation of metabolites related to glycine, serine, and threonine metabolism. This study suggests that adding fungi to the larval diet significantly affects black soldier fly larval metabolomics. Further research is needed to understand how individual amino acids and their metabolites contributed by fungi affect black soldier fly larval physiology, growth, and development, to elucidate the interaction between fungal nutrients and black soldier fly physiology.

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

The industrial rearing of the yellow mealworm (Tenebrio molitor) for feed and food purposes on agricultural by-products may expose larvae and adults to entomopathogens used as biocontrol agents in crop production. Bacterial spores/toxins or fungal conidia from species such as Bacillus thuringiensis or Metarhizium brunneum could affect the survival and growth of insects. Therefore, the aim of this study was to investigate the potential benefits of a wheat bran diet supplemented with probiotic bacteria and dried egg white on larval development and survival and its effects on the gut microbiome composition. Two probiotic bacterial species, Pediococcus pentosaceus KVL B19-01 and Lactiplantibacillus plantarum WJB, were added to wheat bran feed with and without dried egg white, as an additional protein source, directly from neonate larval hatching until reaching a body mass of 20 mg. Subsequently, larvae from the various diets were exposed for 72 h to B. thuringiensis, M. brunneum, or their combination. Larval survival and growth were recorded for 14 days, and the bacterial microbiota composition was analyzed using 16S rDNA sequencing prior to pathogen exposure and on days 3 and 11 after inoculation with the pathogens. The results showed increased survival for T. molitor larvae reared on feed supplemented with P. pentosaceus in the case of co-infection. Larval growth was also impacted in the co-infection treatment. No significant impact of egg white or of P. pentosaceus on larval growth was recorded, while the addition of Lb. plantarum resulted in a minor increase in individual mass gain compared with infected larvae without the latter probiotic. On day 14, B. thuringiensis was no longer detected and the overall bacterial community composition of the larvae was similar in all treatments. On the other hand, the relative operational taxonomic unit (OTU) abundance was dependent on day, diet, and probiotic. Interestingly, P. pentosaceus was present throughout the experiments, while Lb. plantarum was not found at a detectable level, although its transient presence slightly improved larval performance. Overall, this study confirms the potential benefits of some probiotics during the development of T. molitor while underlining the complexity of the relationship between the host and its microbiome.

Improving the nutritional values of yellow mealworm Tenebrio molitor (Coleoptera: Tenebrionidae) larvae as an animal feed ingredient: a review

Yellow mealworm larvae (YML; Tenebrio molitor) are considered as a valuable insect species for animal feed due to their high nutritional values and ability to grow under different substrates and rearing conditions. Advances in the understanding of entomophagy and animal nutrition over the past decades have propelled research areas toward testing multiple aspects of YML to exploit them better as animal feed sources. This review aims to summarize various approaches that could be exploited to maximize the nutritional values of YML as an animal feed ingredient. In addition, YML has the potential to be used as an antimicrobial or bioactive agent to improve animal health and immune function in production animals. The dynamics of the nutritional profile of YML can be influenced by multiple factors and should be taken into account when attempting to optimize the nutrient contents of YML as an animal feed ingredient. Specifically, the use of novel land-based and aquatic feeding resources, probiotics, and the exploitation of larval gut microbiomes as novel strategies can assist to maximize the nutritional potential of YML. Selection of relevant feed supplies, optimization of ambient conditions, the introduction of novel genetic selection procedures, and implementation of effective post-harvest processing may be required in the future to commercialize mealworm production. Furthermore, the use of appropriate agricultural practices and technological improvements within the mealworm production sector should be aimed at achieving both economic and environmental sustainability. The issues highlighted in this review could pave the way for future approaches to improve the nutritional value of YML.

Impact of gut microbiota composition on black cutworm, Agrotis ipsilon (hufnagel) metabolic indices and pesticide degradation

Endosymbionts are known to have significant effects on their insect hosts, including nutrition, reproduction, and immunity. Insects gut microbiota is a critical component that affects their physiological and behavioral characteristics. The black cutworm (BCW), Agrotis ipsilon, is an economically important lepidopteran pest that has a diverse gut microbiome composed of nine species belonging to three phyla: Proteobacteria, Actinobacteria, and Firmicutes. This study was conducted to investigate the diversity of gut bacteria isolated from BCW larvae and moths and their effects on metabolism and pesticide degradation. The bacterial isolates were identified using the 16 S rRNA gene. The study showed that the gut microbiome composition significantly affected the metabolism of BCW larvae. Based on the screening results of synthesis of digestive enzymes and pesticide degradation, Brachybacterium conglomeratum and Glutamicibacter sp were selected to perform the remaining experiments as single isolates and consortium. The consortium-fed larvae showed high metabolic indices compared to antibiotic-fed larvae and the control. The gut bacteria were also shown to degrade three pesticide groups. Concerns regarding the health risk of chlorpyrifos have been raised due to its extensive use in agriculture. The isolated B. conglomeratum was more effective in chlorpyrifos degradation than the consortium. Furthermore, the study also examined the presence of sex related endosymbionts (Wolbachia, Spiroplasma, and Rickettsia) in the reproductive tissues of adults. The outcomes demonstrated that none of the examined endosymbionts existed. In conclusion, the study highlights the importance of the gut microbiome in insect physiology and behavior and its potential applications in biotechnology. It provides insights into developing eco-friendly pest control and bioremediation strategies using gut bacteria.

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

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.

Bugs in Bugs: The Role of Probiotics and Prebiotics in Maintenance of Health in Mass-Reared Insects

Simple Summary

The importance of insect farming is increasing in the livestock market by evolving into a form of intensive production that is often characterized by a high density of individuals kept in closed environments. These conditions can cause a higher risk of occurrence of insect diseases and the lowering of reproductive and growth performances. The role of microbiota composition in insect behaviour and health maintenance could be further studied for selecting microorganisms that act as probiotics for the main mass reared insect species. These probiotics could enhance host performances and reduce the incidence of risks related to insect diseases.

Abstract

Interactions between insects and their microbiota affect insect behaviour and evolution. When specific microorganisms are provided as a dietary supplement, insect reproduction, food conversion and growth are enhanced and health is improved in cases of nutritional deficiency or pathogen infection. The purpose of this review is to provide an overview of insect–microbiota interactions, to review the role of probiotics, their general use in insects reared for food and feed, and their interactions with the host microbiota. We review how bacterial strains have been selected for insect species reared for food and feed and discuss methods used to isolate and measure the effectiveness of a probiotic. We outline future perspectives on probiotic applications in mass-reared insects.