Self-Selection of Feeding Substrates by Tenebrio molitor Larvae of Different Ages to Determine Optimal Macronutrient Intake and the Influence on Larval Growth and Protein Content

Characterisation of Tenebrio molitor Reared on Substrates Supplemented with Chestnut Shell

Tenebrio molitor larvae represent a sustainable protein source for food and feed. The aim of this study was to evaluate the supplementation of chestnut shell, a by-product of the agro-industrial chain, in growth substrates for T. molitor larvae rearing. Seven-week-old larvae were reared on three different growth substrates: the control group (CTRL) was fed wheat bran, treatment group one was fed wheat bran supplemented with 12.5% w/w chestnut shell (TRT1), and treatment group two was fed wheat bran supplemented with 25% w/w chestnut shell (TRT2). Larval weight, substrate consumption, and mortality were recorded weekly. After 14 days, insect meals were produced for bromatological and colorimetric analysis, and bacterial inhibition activity assay using a microdilution method. The amino acid profile of insects was determined using quantitative nuclear magnetic resonance spectroscopy. Our results showed a lower feed conversion ratio and higher larval survival rate % in TRT2 compared to CTRL (p < 0.05). Proteins and lipids of TRT2 were higher than other groups (p < 0.05). Important differences were observed in the amino acid profile of TRT1 and TRT2 compared to CTRL (p < 0.05). TRT1 and TRT2 showed higher E. coli inhibitory activity than CTRL (p < 0.05). In conclusion, chestnut shell supplementation improved the survival and functional characteristics of larvae and likely impacted the insects' metabolism.

Duplications and Losses of the Detoxification Enzyme Glycosyltransferase 1 Are Related to Insect Adaptations to Plant Feeding

Insects have developed sophisticated detoxification systems to protect them from plant secondary metabolites while feeding on plants to obtain necessary nutrients. As an important enzyme in the system, glycosyltransferase 1 (GT1) conjugates toxic compounds to mitigate their harm to insects. However, the evolutionary link between GT1s and insect plant feeding remains elusive. In this study, we explored the evolution of GT1s across different insect orders and feeding niches using publicly available insect genomes. GT1 is widely present in insect species; however, its gene number differs among insect orders. Notably, plant-sap-feeding species have the highest GT1 gene numbers, whereas blood-feeding species display the lowest. GT1s appear to be associated with insect adaptations to different plant substrates in different orders, while the shift to non-plant feeding is related to several losses of GT1s. Most large gene numbers are likely the consequence of tandem duplications showing variations in collinearity among insect orders. These results reveal the potential relationships between the evolution of GT1s and insect adaptation to plant feeding, facilitating our understanding of the molecular mechanisms underlying insect-plant interactions.

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

By-product-based diets have the potential to improve the environmental and economic sustainability of Tenebrio molitor (Linnaeus, 1758) production. However, evaluations of the efficacy of new diets are generally focused on larval performance, while the effect on adults is poorly understood. This aim of this study was to evaluate diets enriched with tomato pomace over a complete breeding cycle. The results showed that when used as an oviposition substrate, all the tested diets, including tomato pomace (T), outperformed the control bran-yeast diet (WY, 95:5 ratio), possibly due to the presence of cholesterol and linoleic acid. The adults fed with the bran-tomato pomace-brewer's spent grain diet (WTB, 50:27:23 ratio), the bran-tomato pomace-yeast diet (WTY, 50:41:9 ratio), and the bran-tomato pomace diet (WT, 50:50 ratio) produced significantly more larvae than those fed with the WY diet. The WTB diet (despite being yeast-free) performed similarly to the WY control diet during the subsequent larval growth phase, making it suitable for the entire production cycle. In conclusion, the results show that tomato pomace can be used a valid by-product in the formulation of efficient diets for the breeding of T. molitor and also provide an alternative to expensive yeast.

Exploiting Agri-Food Waste as Feed for Tenebrio molitor Larvae Rearing: A Review

The agri-food industry generates substantial amounts of waste, including by-products and residues. The increasing demand for sustainable and eco-friendly practices in the agri-food sector has sparked an interest in finding alternative uses for such waste materials. One promising approach is the utilization of waste from the agri-food industry as feed for the rearing of mealworms (Tenebrio molitor). Since agri-food waste is rich in proteins, carbohydrates, lipids, and vitamins, as well as other bioactive compounds, all of which are essential for insect growth and development, incorporating such waste into the diet of mealworms promotes sustainable insect production, reducing the economic and environmental problems associated with waste disposal. This practice can also be beneficial for the rearing of mealworms since their nutritional value can also be enhanced. To this end, various waste materials, such as fruit and vegetable peels, spent grains, and food processing residues, have been investigated as potential feed sources, leading to increased mass production, lower cost, and enhanced nutritional value. This review aims to highlight the potential of agri-food waste as a feed source for mealworms, as well as their potential to enhance their nutritional value. Furthermore, the potential applications of mealworms reared on agri-food waste are highlighted, including their potential as a sustainable protein source for human consumption and as feed ingredients in the livestock and aquaculture sectors.

Social administration of juvenile hormone to larvae increases body size and nutritional needs for pupation

Social insects often display extreme variation in body size and morphology within the same colony. In many species, adult morphology is socially regulated by workers during larval development. While larval nutrition may play a role in this regulation, it is often difficult to identify precisely what larvae receive from rearing workers, especially when larvae are fed through social regurgitation. Across insects, juvenile hormone is a major regulator of development. In the ant Camponotus floridanus, this hormone is present in the socially regurgitated fluid of workers. We investigated the role the social transfer of juvenile hormone in the social regulation of development. To do this, we administered an artificial regurgitate to larvae through a newly developed handfeeding method that was or was not supplemented with juvenile hormone. Orally administered juvenile hormone increased the nutritional needs of larvae, allowing them to reach a larger size at pupation. Instead of causing them to grow faster, the juvenile hormone treatment extended larval developmental time, allowing them to accumulate resources over a longer period. Handfeeding ant larvae with juvenile hormone resulted in larger adult workers after metamorphosis, suggesting a role for socially transferred juvenile hormone in the colony-level regulation of worker size over colony maturation.

Future Proteins: Sustainable Diets for Tenebrio molitor Rearing Composed of Food By-Products

Since the human population is continuously growing, sufficient food with low environmental impact is required. Especially, the challenge of providing proteins will deepen and insects can contribute to a more sustainable and efficient source of protein for human consumption. Tenebrio molitor larvae are highly nutritious and rearing mealworms is more environmentally friendly compared to the production of traditional livestock meat. To use T. molitor as a more sustainable alternative to conventional proteins, it is essential to apply diets from a local and sustainable source. Therefore, the objective of this study was to find local by-products or leftovers which can be used in mass production of larvae as a main substrate. Feeding trials investigating twenty-nine different substrates were conducted to evaluate larval growth performance and adult reproduction by determining development times, survival rates, biomass, and fecundity. Several suitable by-products were identified that can be used in high quantities as single component diet for T. molitor rearing, revealing a high survival rate, short development time, high mean total biomass, and successful breeding. The most successful substrate-malt residual pellets-was found to be an alternative to the most used substrate, wheat bran. Furthermore, corn germ meal, sweet chestnuts, bread remains, soybeans, sweet potatoes, and wheat germs have been discovered to be suitable diets for T. molitor. Moreover, the findings of this study contribute towards using several substrates as supplements.

A review on edible insects in China: Nutritional supply, environmental benefits, and potential applications

This review explored the potential of edible insects to address the challenges of malnutrition and food security. Although grain production in China has met the Food and Agriculture Organization standards, the shortage of protein supply is still a big issue. Moreover, expanding livestock farming is considered unsustainable and environmentally unfriendly. Edible insects have become an alternative with higher sustainable and ecological properties. There are 324 species of insects currently consumed in China, and they have high nutritional value, with a rich source of protein and unsaturated fatty acids. Insect farming provides numerous benefits, including green feeds for livestock, poultry, and aquaculture, sustainable organic waste management, as well as industrial and pharmaceutical raw materials. The food toxicological evaluations conducted in China indicated that edible insects are safe for general consumption by the Chinese, but allergies and other related food safety issues should not be ignored. Consumer acceptance is another barrier to overcome, with different schemas between China and Western countries. More research on the potential functions of edible insects and their product development may enhance their acceptance in China. Overall, incorporating edible insects into our diet is a promising solution to address challenges related to protein supply and food security. To ensure safety and sustainability, appropriate legislation, quality regulations, large-scale insect farms, and acceptable processing techniques are necessary. Moreover, more scientific research and social awareness are required to promote the culture and utilization of edible insects in China.

Enhancing the Nutritional Profile of Tenebrio molitor Using the Leaves of Moringa oleifera

Nowadays, more and more research is being carried out on various feeds of Tenebrio molitor larvae, in order to increase their nutritional value and render them a valuable component of the human diet. In this study, Moringa oleifera leaves were used in different proportions (up to 50%) to substitute wheat bran (the usually employed feed), in order to evaluate their effect on the growth and development of the larvae, as well as on their composition in crude protein, fat and fatty acids, ash, vitamins, and antioxidants. It was found that the addition of M. oleifera leaves in the feed had no negative impact on the development and survival of the insects, while an increase in their nutritional value was recorded. More specifically, an increase in the crude protein of up to 22.61% and vitamin C and A contents of up to 40.74% and 491.63%, respectively, was recorded. Therefore, the use of M. oleifera leaves as a feed additive is highly recommended for rearing T. molitor larvae to enhance the nutritional value of the insects.

Analysis of the Composition of Different Instars of Tenebrio molitor Larvae using Near-Infrared Reflectance Spectroscopy for Prediction of Amino and Fatty Acid Content

Insects are a sustainable protein source for food and feed. The yellow mealworm (Tenebrio molitor L.) is a promising candidate for industrial insect rearing and was the focus of this study. This research revealed the diversity of Tenebrio molitor larvae in the varying larval instars in terms of the nutritional content. We hypothesized that water and protein are highest in the earlier instar, while fat content is very low but increases with larval development. Consequently, an earlier instar would be a good choice for harvest, since proteins and amino acids content decrease with larval development. Near-infrared reflectance spectroscopy (NIRS) was represented in this research as a tool for predicting the amino and fatty acid composition of mealworm larvae. Samples were scanned with a near-infrared spectrometer using wavelengths from 1100 to 2100 nm. The calibration for the prediction was developed with modified partial least squares (PLS) as the regression method. The coefficient for determining calibration (R²_C) and prediction (R²_P) were >0.82 and >0.86, with RPD values of >2.20 for 10 amino acids, resulting in a high prediction accuracy. The PLS models for glutamic acid, leucine, lysine and valine have to be improved. The prediction of six fatty acids was also possible with the coefficient of the determination of calibration (R²_C) and prediction (R²_P) > 0.77 and >0.66 with RPD values > 1.73. Only the prediction accuracy of palmitic acid was very weak, which was probably due to the narrow variation range. NIRS could help insect producers to analyze the nutritional composition of Tenebrio molitor larvae fast and easily in order to improve the larval feeding and composition for industrial mass rearing.

Waste Orange Peels as a Feed Additive for the Enhancement of the Nutritional Value of Tenebrio molitor

Lately, additional attention is being placed on edible insects, since they constitute an excellent, cost-efficient source of proteins with a low ecological footprint. Tenebrio molitor was the first insect that was considered edible by EFSA in 2021. This species can replace conventional protein sources and thus, it has the potential to be used in many different food products. In the present study, a food by-product that is commonly produced (i.e., albedo orange peel waste) was used as a feed additive for T. molitor larvae, in an effort to further improve the circular economy and enhance the nutritional value of the insects. To this end, bran, which is commonly used as feed for T. molitor larvae, was fortified with the albedo orange peel waste (up to 25% w/w). Larval performance, in terms of larval survival and growth, as well as the larval nutritional value, i.e., the content of protein, fat, carbohydrates, ash, carotenoids, vitamins A and C, and polyphenols, was evaluated. Based on the results, the increase in the percentage of orange peel albedos in T. molitor feed resulted in a subsequent increase in the content of larvae in carotenoids and vitamin A up to 198%, in vitamin C up to 46%, and an increase in the protein and ash content up to 32% and 26.5%, respectively. Therefore, the use of albedo orange peel waste for feeding of T. molitor larvae is highly recommended, since it results in larvae with enhanced nutritional value and at the same time, the utilization of this feeding substrate further lowers the cost of insect farming.

Near-Infrared Reflectance Spectroscopy for Quantitative Analysis of Fat and Fatty Acid Content in Living Tenebrio molitor Larvae to Detect the Influence of Substrate on Larval Composition

Several studies have shown that mealworms (Tenebrio molitor L.) could provide animals and humans with valuable nutrients. Tenebrio molitor larvae were studied to determine whether their rearing diets affected their fat and fatty acid content and to ascertain if it is possible to detect the changes in the larval fat composition using near-infrared reflectance spectroscopy (NIRS). For this reason, a standard control diet (100% wheat bran) and an experimental diet, consisting of wheat bran and the supplementation of a different substrate (coconut flour, flaxseed flour, pea protein flour, rose hip hulls, grape pomace, or hemp protein flour) were used. The results showed lesser weight gain and slower growth rates for larvae raised on diets with a high fat content. A total of eight fatty acids were identified and quantified, where palmitic, oleic, and linoleic acids were the most prevalent and showed a correlation between larval content and their content in the rearing diets. There was a high content of lauric acid (3.2-4.6%), myristic acid (11.4-12.9%), and α-linolenic acid 8.4-13.0%) in mealworm larvae as a result of the high dietary content of these fatty acids. NIR spectra were also influenced by the fat and fatty acid composition, as larval absorbance values differed greatly. The coefficient of the determination of prediction (R²_P) was over 0.97, with an RPD value of 8.3 for the fat content, which indicates the high predictive accuracy of the NIR model. Furthermore, it was possible to develop calibration models with great predictive efficiency (R²_P = 0.81-0.95, RPD = 2.6-5.6) for all fatty acids, except palmitoleic and stearic acids which had a low predictive power (R²_P < 0.5, RPD < 2.0). The detection of fat and fatty acids using NIRS can help insect producers to quickly and easily analyze the nutritional composition of mealworm larvae during the rearing process.

Carob (Ceratonia siliqua) as Functional Feed Is Beneficial in Yellow Mealworm (Tenebrio molitor) Rearing: Evidence from Growth, Antioxidant Status and Cellular Responses

In terms of sustainability and circular economy, agricultural by-products may be efficiently reused in insects’ rearing for high-quality protein sources in human diet and animal feeds. The present study aimed to explore whether the utilization of carob pods as feeding substrate may beneficially affect Tenebrio molitor’s growth, nutritional value, antioxidant status and cellular responses. Increasing levels of milled whole carob pods (0, 25, 50, 75, 100%) were used as alternative wheat bran (control) substrates for yellow mealworm rearing, while growth performance, proximate composition, total phenolic content, antioxidant enzyme activity and the expression of stress- and apoptotic-related proteins were evaluated in larvae. The results showed that carob pods’ content up to 75% did not significantly differentiate larvae weight, development time and total dry matter. Larvae total phenolic content and antioxidant activity exhibited a significant increase at 75% content. Although the antioxidant enzymes’ activity decreased at both 25 and 50% levels, higher carob content levels (75 and 100%) resulted in no significant changes compared to the control. Carob pods led to decreased apoptotic indicators and the low expression of most stress-related proteins compared to the control. The present findings demonstrate that carob pods and their antioxidant properties exert beneficial effects on T. molitor’s rearing and nutritional status, although 100% carob content may impact adversely the larvae due to the high amounts of carob tannins.