The catabolism of glucose in Tenebrio molitor: The effects of corpora cardiaca

During the development of the mealworm Tenebrio molitor, the effects of corpora cardiaca (CC) extracts on glucose catabolism were tested. In control insects and in insects receiving CC extracts, the activity of the pentose cycle and the glycolytic-citric acid cycle, were evaluated in vivo by a radiorespirometric method using [1-¹⁴C] glucose and [6-¹⁴C] glucose as substrates. The CC extracts strongly divert glucose from the pentose phosphate pathway, which is very active in Tenebrio molitor. Glucose oxidation is reduced by the CC extracts in pupae and adults but is increased in last instar larvae. It seems that the effects of CC extracts vary depending upon the state of carbohydrate reserves.     

A comparative toxic effect of Cedrus deodara oil on larval protein contents and its behavioral effect on larvae of mealworm beetle (Tenebrio molitor) (Coleoptera: Tenebrionidae)

Cedrus deodara (deodar) is practically used, as insect repellent, in the northern areas of Pakistan but no data available therefore this study was conducted to evaluate the effectiveness of deodar oil as an alternate of conventional insecticides against the larval pest stage of mealworm beetle (Tenebrio molitor), by feeding method. The aim of the study was to investigate the effectiveness of deodar oil as an alternate of conventional insecticides against the larval pest stage of mealworm beetle (Tenebrio molitor), by feeding method. All tested chemicals showed efficacy against the pests. The LC₅₀ was determined by probit analysis and was found to be 3.41, 0.086 and 0.023% of larvae treated with deodar oil, Carbosulfan and Imidacloprid respectively The LC₅₀ treated larvae were subjected to the evaluation of protein activity, qualitatively and quantitatively. The protein level in tested insects was enhanced when treated with Imidacloprid, Carbosulfan and deodar oil. The electrophoretic profile of treated insects showed more bands in insects treated with Cedrus deodara oil. This electrophoretic profile appeared in 4, 5, 7 and 8 bands for tested chemicals including control. Antifeedant activity was observed for C. deodara as larvae were deterred to feed on the food found in the container.     

Selective breeding and characterization of a black mealworm strain of Tenebrio molitor Linnaeus (Coleoptera: Tenebrionidae)

Larvae of Tenebrio molitor Linnaeus are edible insects and are approved as a food ingredient in Korea. They are typically yellow; however, rare black larvae have been found in breeding boxes at insect farms. It is not clear whether black larvae represent a different species that invaded and hybridized with the yellow larvae of T. molitor or whether T. molitor shows intraspecific color variation. In this study, we characterized and identified black larvae for applications in industrial fields as well as accurate breeding and management. First, in a comparative analysis, we did not detect differences in the morphological characteristics of yellow and black larvae and adults, with the exception of larval body color. For accurate species identification, molecular analyses (p-distances and neighbor-joining) were performed based on partial COI sequences of 33 yellow and seven black larvae. Genetic divergence between yellow and black larvae ranged from 0.0% to 2.1%, revealing intraspecific variation. A neighbor-joining analysis strongly supported the classification of the two morphs as a single species. Black larvae were separated from yellow larvae and maintained by selective breeding. As a result, black larvae were completely fixed in the F2 generation (F1 = 96% and F2 = 100%). Yellow and black larvae showed no significant differences in developmental characteristics and fecundity. These findings improve our understanding of diversity within an important edible insect species and contribute to quality assurance in the food industry based on clear species identification.     

Sodium Solute Symporter and Cadherin Proteins Act as Bacillus thuringiensis Cry3Ba Toxin Functional Receptors in Tribolium castaneum

Understanding how Bacillus thuringiensis (Bt) toxins interact with proteins in the midgut of susceptible coleopteran insects is crucial to fully explain the molecular bases of Bt specificity and insecticidal action. In this work, aminopeptidase N (TcAPN-I), E-cadherin (TcCad1), and sodium solute symporter (TcSSS) have been identified by ligand blot as putative Cry3Ba toxin-binding proteins in Tribolium castaneum (Tc) larvae. RNA interference knockdown of TcCad1 or TcSSS proteins resulted in decreased susceptibility to Cry3Ba toxin, demonstrating the Cry toxin receptor functionality for these proteins. In contrast, TcAPN-I silencing had no effect on Cry3Ba larval toxicity, suggesting that this protein is not relevant in the Cry3Ba toxin mode of action in Tc. Remarkable features of TcSSS protein were the presence of cadherin repeats in its amino acid sequence and that a TcSSS peptide fragment containing a sequence homologous to a binding epitope found in Manduca sexta and Tenebrio molitor Bt cadherin functional receptors enhanced Cry3Ba toxicity. This is the first time that the involvement of a sodium solute symporter protein as a Bt functional receptor has been demonstrated. The role of this novel receptor in Bt toxicity against coleopteran insects together with the lack of receptor functionality of aminopeptidase N proteins might account for some of the differences in toxin specificity between Lepidoptera and Coleoptera insect orders.     

Screening for mycotoxins with larvae of Tenebrio molitor.

Larvae of the yellow mealworm, Tenebrio molitor, were used to screen isolates of field and storage fungi, included in their dietary substrate, for mycotoxins. Feeding of three isolates of Fusarium roseum, two of Fusarium equiseti and of Fusarium nivale, and one of an unidentified species of Fusarium resulted in growth depression of the larvae. One isolate of an unidentified species of Myrothecium was also toxic to larvae of Tenebrio molitor. Mycotoxin production was apparently dependent, not only on the fungal isolate, but also on the culture conditions under which the fungus was grown. Some fungal isolates had growth-promoting qualities for larvae of Tenebrio molitor.     

Food Value of Mealworm Grown on Acrocomia aculeata Pulp Flour

Insects have played an important role as human food throughout history, especially in Africa, Asia and Latin America. A good example of edible insects is the mealworm, Tenebrio molitor Linnaeus, 1758 (Coleoptera, Tenebrionidae), which are eaten in Africa, Asia, the Americas and Australia. This species is easily bred in captivity, requiring simple management. The bocaiuva (Acrocomia aculeata (Jacq.) Lodd) is an abundant palm tree found in the Brazilian Cerrado, providing fruits with high nutritional value. The aim of this work was to determine the chemical composition of T. molitor grown in different artificial diets with bocaiuva pulp flour. The nutritional composition, fatty acid composition, antioxidant activity, trypsin activity and anti-nutritional factors of larvae were analyzed. The results showed that mealworms grown on artificial diet with bocaiuva are a good source of protein (44.83%) and lipid (40.45%), with significant levels of unsaturated fatty acids (65.99%), antioxidant activity (4.5 μM Trolox/g of oil extracted from larvae) and absence of anti-nutritional factors. This study indicates a new source of biomass for growing mealworms and shows that it is possible to breed mealworms in artificial diet with bocaiuva flour without compromising the nutritional quality of the larvae.     

A reinvestigation of the effects of cortisol on growth in insects

Incorporation of cortisol, or various derivatives and analogues of cortisol, into the diet had no effect on the rate of growth of Tenebrio molitor. Injections of cortisol, or its derivatives, into fourth instar larvae of Schistocerca americana gregaria, had no effect on their rate of growth. The moult to fifth instar was normal. Administration in the diet, or injections of cortisol had no effect on the rate of growth of fourth and fifth instar larvae of Manduca sexta, or on the insect's uptake and utilization of food. The development of larvae to pupae and adults was unaffected. It is concluded, contrary to the findings of two previously published reports, that the vertebrate hormone cortisol does not affect the growth and development of insects.     

Risk assessment system establishment for evaluating the potential impacts of imported Bacillus thuringiensis maize on a non-target insect,Tenebrio molitor

Large amounts of genetically modified grains producing Bacillus thuringiensis (Bt) toxins have been imported to Korea. Therefore, the establishment of a risk assessment system for evaluating the potential impacts of imported Bt maize on non-target insects is important. Before evaluating the environmental impacts of Bt grains of unknown origin, Cry protein types must first be identified in test Bt grains. Cry toxins of imported Bt maize grains were analyzed by ELISA. Because all tested Bt maize grains contained Cry1A, Tenebrio molitor, a non-lepidopteran species, was selected as the non-target insect species. A domestic maize strain that showed few differences in nutritional composition compared to the Bt maize grain was used as the alternative non-Bt control. Slightly increased survival rate and head capsule width of Bt maize-fed T. molitor were observed, indicating that Bt maize has no sub-chronic adverse effects on T. molitor. An ELISA test revealed that concentrations of Cry1A toxins slowly increased in the body of T. molitor when the insects were fed Bt maize. Such substantial amounts of Cry toxins remaining in the alimentary tract of larvae indicate that Cry toxins can be transferred to the higher trophic level of predatory insects. However, no Cry proteins were detected in the hemolymph of the Bt maize-fed larvae, suggesting that there is little possibility of Cry toxin exposure via T. molitor to the higher endoparasitoids. The risk assessment strategies and protocols established in this study may also be applicable to other imported Bt crops in Korea.     

Effect of hydrocortisone on the growth and development of larvae Tenebrio molitor

Hydrocortisone administered with the food causes inhibition of growth in larvae Tenebrio molitor. Hydrocortisone together with the reduction in the rate of growth retards the moulting cycle in larvae T. molitor. The action of hydrocortisone does not influence greatly the number of larvae moulting cycles.     

An exploration on greenhouse gas and ammonia production by insect species suitable for animal or human consumption

Background

Greenhouse gas (GHG) production, as a cause of climate change, is considered as one of the biggest problems society is currently facing. The livestock sector is one of the large contributors of anthropogenic GHG emissions. Also, large amounts of ammonia (NH₃), leading to soil nitrification and acidification, are produced by livestock. Therefore other sources of animal protein, like edible insects, are currently being considered.

Methodology/Principal Findings

An experiment was conducted to quantify production of carbon dioxide (CO₂) and average daily gain (ADG) as a measure of feed conversion efficiency, and to quantify the production of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O) as well as NH₃ by five insect species of which the first three are considered edible: Tenebrio molitor, Acheta domesticus, Locusta migratoria, Pachnoda marginata, and Blaptica dubia. Large differences were found among the species regarding their production of CO₂ and GHGs. The insects in this study had a higher relative growth rate and emitted comparable or lower amounts of GHG than described in literature for pigs and much lower amounts of GHG than cattle. The same was true for CO₂ production per kg of metabolic weight and per kg of mass gain. Furthermore, also the production of NH₃ by insects was lower than for conventional livestock.

Conclusions/Significance

This study therefore indicates that insects could serve as a more environmentally friendly alternative for the production of animal protein with respect to GHG and NH₃ emissions. The results of this study can be used as basic information to compare the production of insects with conventional livestock by means of a life cycle analysis.     

For uptake of yolk precursors,epithelial cell-oocyte gap junctional communication is required by insects representing six different orders

For uptake of vitellogenin protein into nascent yolk spheres, communication through open gap junction channels between the follicle epithelium and oocyte is required by six different insects representing six different orders. It was recently shown in the hemipteran, Oncopeltus fasciatus, that endocytic uptake of yolk protein resulting in the formation of nascent yolk spheres depended upon an intact epithelium communicating with the oocyte through patent gap junctions. Following treatment with octanol, which down-regulated gap junctions below the level of dye coupling, vitellogenin uptake was terminated. Yet, for another hemipteran, Dysdercus intermedius, it has been shown that yolk spheres can form even when all epithelial cells have been stripped from the oocyte. To determine if the mechanism seen in Oncopeltus is present in other insects, we utilized the same techniques to study nascent yolk sphere production in a dipteran, Drosophila melanogaster, a lepidopteran, Actias luna, a hymenopteran, Xylocopa virginica, a coleopteran, Tenebrio molitor and an orthopteran, Acheta domesticus. In each of these, when gap junctions were down-regulated yolk uptake quickly stopped. That six different insects from six different orders all required a gap junctionally transmitted chemical signal of epithelial cell origin suggests that this mechanism is widespread throughout the insects.     

Toxin-binding proteins isolated from yellow mealworm <Emphasis Type="Italic">Tenebrio molitor</Emphasis> and wax moth <Emphasis Type="Italic">Galleria mellonella</Emphasis>

A 67-kDa protein that can specifically bind the activated Cry9A endotoxin under ligand-blotting conditions was purified from midgut epithelium apical membranes of wax moth Galleria mellonella by affinity chromatography. N-Terminal amino acid sequencing enabled identification of this protein as aminopeptidase N. In similar experiments, 66- and 58-kDa proteins specific to endotoxin Cry3A were isolated from the midgut epithelium apical membranes of Tenebrio molitor larvae. Mass spectrometry showed close similarity of the 58-kDa protein to the Tenebrio molitor α-amylase.     

Growth performance and feed conversion efficiency of three edible mealworm species (Coleoptera: Tenebrionidae) on diets composed of organic by-products

Insects receive increasing attention as an alternative protein-rich food source for humans. Producing edible insects on diets composed of organic by-products could increase sustainability. In addition, insect growth rate and body composition, and hence nutritional quality, can be altered by diet.Three edible mealworm species Tenebrio molitor L., Zophobas atratus Fab. and Alphitobius diaperinus Panzer were grown on diets composed of organic by-products originating from beer brewing, bread/cookie baking, potato processing and bioethanol production. Experimental diets differed with respect to protein and starch content. Larval growth and survival was monitored. Moreover, effects of dietary composition on feed conversion efficiency and mealworm crude protein and fatty acid profile were assessed. Diet affected mealworm development and feed conversion efficiency such that diets high in yeast-derived protein appear favourable, compared to diets used by commercial breeders, with respect to shortening larval development time, reducing mortality and increasing weight gain. Diet also affected the chemical composition of mealworms. Larval protein content was stable on diets that differed 2–3-fold in protein content, whereas dietary fat did have an effect on larval fat content and fatty acid profile. However, larval fatty acid profile did not necessarily follow the same trend as dietary fatty acid composition. Diets that allowed for fast larval growth and low mortality in this study led to a comparable or less favourable n6/n3 fatty acid ratio compared to control diets used by commercial breeders. In conclusion, the mealworm species used in this study can be grown successfully on diets composed of organic by-products. Diet composition did not influence larval protein content, but did alter larval fat composition to a certain extent.     

Effects of host nutrition on virulence and fitness of entomopathogenic nematodes: Lipid- and protein-based supplements in Tenebrio molitor diets

Entomopathogenic nematodes, Heterorhabditis indica and Steinernema riobrave, were tested for virulence and reproductive yield in Tenebrio molitor that were fed wheat bran diets with varying lipid- and protein-based supplements. Lipid supplements were based on 20% canola oil, peanut, pork or salmon, or a low lipid control (5% canola). Protein treatments consisted of basic supplement ingredients plus 0, 10, or 20% egg white; a bran-only control was also included. Some diet supplements had positive effects on nematode quality, whereas others had negative or neutral effects. All supplements with 20% lipids except canola oil caused increased T. molitor susceptibility to H. indica, whereas susceptibility to S. riobrave was not affected. Protein supplements did not affect host susceptibility, and neither lipid nor protein diet supplements affected reproductive capacity of either nematode species. Subsequently, we determined the pest control efficacy of progeny of nematodes that had been reared through T. molitor from different diets against Diaprepes abbreviatus and Otiorhynchus sulcatus. All nematode treatments reduced insect survival relative to the control (water only). Nematodes originating from T. molitor diets with the 0% or 20% protein exhibited lower efficacy versus D. abbreviatus than the intermediate level of protein (10%) or bran-only treatments. Nematodes originating from T. molitor lipid or control diets did not differ in virulence. Our research indicates that nutritional content of an insect host diet can affect host susceptibility to entomopathogenic nematodes and nematode fitness; therefore, host media could conceivably be optimized to increase in vivo nematode production efficiency.     

Transepithelial transport of salicylate by the Malpighian tubules of insects from different orders

The organic anion salicylate is a plant secondary metabolite that protects plants against phytophagous insects. In this study, a combination of salicylate-selective microelectrodes and a radioisotope tracer technique was used to study the transepithelial transport of salicylate by the Malpighian tubules of 10 species of insects from five orders. Our results show that salicylate is transported into the lumen of the Malpighian tubules in all the species evaluated, except Rhodnius prolixus. The transepithelial transport of salicylate by the Malpighian tubules of Drosophila simulans, Drosophila erecta, Drosophila sechellia, and Acheta domesticus was saturable, Na⁺-dependent and inhibited by α-cyano-4-hydroxycinnamic acid. This transport system resembles that previously found in tubules of Drosophila melanogaster. In contrast, transepithelial transport of salicylate by Malpighian tubules of Tenebrio molitor, Plagiodera versicolora, Aedes aegypti, and Trichoplusia ni was unaffected by Na⁺-free bathing saline. The presence of both salicylate and salicylate metabolites in the secreted fluid samples from the Malpighian tubules of A. domesticus, R. prolixus, T. molitor, and T. ni indicates that insect Malpighian tubules may both transport and metabolize salicylate. The highest capacities to rid the hemolymph of salicylate were found in T. molitor, P. versicolora and Drosphila spp. Our results suggest that transport of salicylate by the Malpighian tubules might contribute to elimination of this organic anion from the hemolymph, particularly in some species that encounter high levels of organic anion in the diet.     

An overview of insect innate immunity

Due to the exposure of insects to various sources of pathogens during different stages of their life cycle and their vulnerability towards subsequent infections, moreover lack of morality issues, economical breeding and short‐term‐life cycle, insect's immunity has been considered as a high‐potential candidate to study underlying mechanisms of defense responses against all sort of invaders, as well as pandemic diseases. Currently, the world is enduring monumental pressure to meet global food production demands. One viable option would be to mass rear edible insects, such as coleopteran meal worm Tenebrio molitor, which is thought to be a substantial protein source. In addition, using antimicrobial peptides as an alternative for antibiotic source against multidrug‐resistant pathogens, makes insects a valuable option to solve this health issue. As a consequence, sufficient knowledge of insect immunity will lead us to reach advanced diagnostic and treatment technologies. To accomplish these goals, crucial importance of identification and functional characterization of the main signaling pathways, such as Toll and immune deficiency (IMD), prompted us to review the mechanisms of the signaling pathways involved in immune response in well‐known insect models.     

Purification and Properties of Ferritin from the Last Instar Larval Hemolymph of Protaetia brevitarsis (Coleoptera)

Ferritin, an iron storage protein, has been purified from the last larval hemolymph of Protaetia brevitarsis (coleoptera) by KBr density gradient ultracentrifugation and resource Q (anion exchange chromatography) using fast performance liquid chromatography (FPLC) system. The iron content of ferritin was determined by atomic emission spectroscopy and FereneS stain. Ferritin of P. brevitarsis is shown to have two different subunits presented on a SDSPAGE in normal (N) and ironinjected (I) hemolymph. SDS PAGE revealed that the ferritin consists of two major polypeptides of 27 and 28 kDa in normal hemolymph. Interestingly, however, 30 kDa subunit was substituted for 28 kDa when iron was injected into the hemolymph. Apporximate isoelectric points of 27 kDa, 28 kDa, and 30 kDa ferritin subunits were 6.7, 6.75, and 6.8, respectively. Ferritin of P. brevitarsis was detected by FereneS stain and confirmed by Western blotting using its polyclonal antibody. Other characteristics such as amino acid composition and Nterminal amino acid sequence were investigated. Amino acid composition of ferritin (N and I) was rich in alanine, glycine, glutamine or glutamic acid and serine, but poor in histidine, arginine, methionine and phenylalanine.     

Cysteine digestive peptidases function as post-glutamine cleaving enzymes in tenebrionid stored-product pests

The major storage proteins in cereals, prolamins, have an abundance of the amino acids glutamine and proline. Storage pests need specific digestive enzymes to efficiently hydrolyze these storage proteins. Therefore, post-glutamine cleaving peptidases (PGP) were isolated from the midgut of the stored-product pest, Tenebrio molitor (yellow mealworm). Three distinct PGP activities were found in the anterior and posterior midgut using the highly-specific chromogenic peptide substrate N-benzyloxycarbonyl-L-Ala-L-Ala-L-Gln p-nitroanilide. PGP peptidases were characterized according to gel elution times, activity profiles in buffers of different pH, electrophoretic mobility under native conditions, and inhibitor sensitivity. The results indicate that PGP activity is due to cysteine and not serine chymotrypsin-like peptidases from the T. molitor larvae midgut. We propose that the evolutionary conservation of cysteine peptidases in the complement of digestive peptidases of tenebrionid stored-product beetles is due not only to the adaptation of insects to plants rich in serine peptidase inhibitors, but also to accommodate the need to efficiently cleave major dietary proteins rich in glutamine.     

Stem‐galling moths provide cetoniine beetles with feeding sites via sap exudation of invasive alien plants

The alien moth Epiblema sugii (Lepidoptera: Tortricidae) induces stem galls on an invasive alien weed, Ambrosia trifida. During summer, along riverbanks in central Japan, the native insects Protaetia brevitarsis, P. orientalis submarumorea (Coleoptera: Scarabaeidae: Cetoniinae), and Camponotus vitiosus (Hymenoptera: Formicidae) feed on the sap exuded from the galls. The cetoniine beetles are highly aggregated among the galls and make wounds on the galls to facilitate sap exudation. Feeding on gall sap may be beneficial to the beetles due to the efficient intake of water and sugar, and the beetles’ inflicting wounds and feeding on the sap seem to have little effect on the gallers. This is a unique finding, where alien plant–galler interaction provides a feeding site for native insects.