Effects of Agro-Industrial Byproduct-Based Diets on the Growth Performance, Digestibility, Nutritional and Microbiota Composition of Mealworm (Tenebrio molitor L.)

Abstract

The aim of this study was to evaluate the effects of agro-industrial byproduct-based diets on the productive parameters, digestibility, insect composition, and gut microbiota of mealworm (Tenebrio molitor) larvae. Three formulations corresponding to three different levels of starch and protein were tested: one formulation based on bread remains and brewer’s yeast, representing a diet of high starch (61.1%) and low crude protein (18.5%) (HS-LP); and two formulations in which an additional four byproducts (courgette (Cucurbita pepo) remains, tigernut (Cyperus scelentus) pulp, brewer’s spent grains, and rice straw) were incorporated in different proportions, consistent with a diet of both moderate starch (29.8%) and crude protein (21.0%) (MS-MP); and another corresponding to a diet of low starch (20.0%) and high crude protein (26.3%) (LS-HP). A total of 1920 young larvae (average weight = 0.65 mg per larva) were used in this study. The larvae were randomly distributed into 16 replicates per treatment (boxes of 22.5 cm × 14.0 cm × 4.75 cm). Ten replicates for the growth performance–digestibility trial and six replicates for the complementary trial to determine uric acid levels in the frass were assigned per treatment. For growth performance, the diets were administered ad libitum during the experiment. The average number of days for the larvae to start pupating was lower in those reared on the HS-LP and LS-HP diets (88.90 and 91.00 days, respectively) than those on the MS-MP diet (120.09 days) (p < 0.001). The final individual weight was higher (p < 0.001) in larvae of the LS-HP group (168.69 mg) compared to those of the other groups (100.29 and 112.99 mg for HS-LP and MS-MP, respectively). However, the feed conversion ratio was better (p < 0.001) in the HS-LP group with the lowest value (1.39 g/g), with dry matter digestibility being the highest for the same diet (70.38%) (p < 0.001). Mealworms reared on LS-HP and MS-MP diets had a higher crude protein content than those reared on the HS-LP diet (p = 0.039). The most abundant phyla in the gut microbiota of larvae were Tenericutes, Proteobacteria, and Firmicutes, with their abundance depending on the rearing substrate. The representation of Tenericutes phylum was higher (p < 0.05) in the mealworms reared on MS-MP and HS-LP diets, whereas Proteobacteria and Cyanobacteria were higher in abundance (p < 0.001) in the insects reared on LS-HP. In conclusion, the larval growth, digestibility, insect composition, and gut microbiota of Tenebrio molitor were found to depend on the composition of the administered diet, and the results suggest great potential for the use of agro-industrial byproducts in their rearing and production.

Shotgun metagenomics reveals the gut microbial diversity and functions in Vespa mandarinia (Hymenoptera: Vespidae) at multiple life stages

“…Previous studies have demonstrated that Tenericutes are directly associated with metabolism, and hosts with a high abundance of Tenericutes exhibit increased insulin sensitivity (Yuan et al, 2021 ). Consequently, their high concentration is helpful for the nutrient intake of larvae, and this phenomenon has been documented in other insects (Montalban et al, 2022 ). By comparison, the ability to use diversified food is an effective way to increase the survival rate for adult wasps.…”

“…Consequently, their high concentration is helpful for the nutrient intake of larvae, and this phenomenon has been documented in other insects (Montalban et al, 2022). By comparison, the ability to use diversified food is an effective way to increase the survival rate for adult wasps.…”

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

“…As has been observed in previous studies, genus abundance also depends on the diet composition provided. Indeed, in larvae fed a higher dietary protein content, the presence of species able to produce cellulolytic enzymes, such as Acinetobacter spp., was reduced ( 63 ). In our study, larvae fed the WB diet showed differences in microbial OTU abundance, resulting in higher loads of Pediococcus spp.…”

Insect-based agri-food waste valorization: Agricultural applications and roles of insect gut microbiota

“…Based on several recent studies on the taxonomic profiling of insects destined for food or animal feed, the dominant microbial groups are summarized in Table 4 . In all observed insect species, the highest abundant phyla of gut bacteria generally belonged to Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes [ [95] , [96] , [97] , [98] , [99] , [100] , [101] , [102] , [103] ]. Regarding the BSF, considered the most efficient biowaste-converting insect species, IJdema et al.…”