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Edible insects such as the mealworm (Tenebrio molitor) are emerging as an alternative animal protein resource to meet the needs of a growing global population. However, despite the successful mass production of edible insects, research into practical compound feed for edible insect is still insufficient. In this study, mealworms were fed wheat bran, layer chicken feed mash, chicken pellets and cattle pellets for 1 to 36 days, after which their body length was measured. In the groups fed with chicken feed mash, chicken pellets or cattle pellets, the mean body lengths were 2.88, 2.92 and 2.95 cm, respectively, similar to the 2.95 cm of the control T. molitor fed with wheat bran. Individual weight measurements yielded similar results: control, 7.87 g; chicken feed mash, 7.43 g; chicken pellets, 7.60 g; and cattle pellets, 7.63 g. Analysis of livestock feed intake showed that the intake was 290.4 g in control insects, 137.7 g in insects fed chicken feed mash, 220.2 g in insects fed chicken pellets and 230.3 g in insects fed cattle pellets. In the excretion analysis, the excretion of the control insects (161.60 g) was larger than that of the insects fed with chicken feed mash (93.37 g), chicken pellets (93.40 g) or cattle pellets (133.87 g). An analysis of the nutritional content of T. molitor based on nine major nutrients showed no significant differences between the control and the test groups. These results can be used to improve the price competitiveness and quality of T. molitor for commercial development. [ABSTRACT FROM AUTHOR]

Selective herbicides are used to control undesirable vegetation or weeds in fields without harming crops. Herbicide use for weed management can directly impact the densities of insect pests in agricultural communities as a result of insect mortality during and immediately after application. In insects, the glutathione S‐transferase (GST) enzyme is involved in both the detoxification process and the defense of cellular membranes against oxidative damage. In this study, two TmGSTs (TmGST‐iso1 and TmGST‐iso2) were identified and characterized to elucidate the GST family in Tenebrio molitor. Among the developmental stages of T. molitor, eggs had the highest expression levels of TmGST‐iso1. TmGST‐iso2 expression was highest in the pre‐pupal stage. TmGST‐iso1 expression was high in the guts of early and late larvae, whereas TmGST‐iso2 expression was not observed in early larvae. Adults, both male and female, had the highest levels of TmGST‐iso1 mRNA expression in the gut and reproductive organs, and the highest levels of TmGST‐iso2 expression in the reproductive organs. Quantitative polymerase chain reaction was used to investigate the impact of treatment with butachlor on the mRNA expression of TmGST‐iso1 and TmGST‐iso2 in larvae. TmGST‐iso1 expression increased in the butachlor‐treated group after 3 and 24 h, whereas TmGST‐iso2 expression peaked at 24 h after treatment. This study provides vital information about the detoxifying activities of T. molitor. [ABSTRACT FROM AUTHOR]

The inhibitor of nuclear factor-kappa B (NF-κB) kinase (IKK) is the core regulator of the NF-κB pathway against pathogenic invasion in vertebrates or invertebrates. IKKβ, -ε and -γ have pivotal roles in the Toll and immune deficiency (IMD) pathways. In this study, a homolog of IKKε (Tm IKKε) was identified from Tenebrio molitor RNA sequence database and functionally characterized for its role in regulating immune signaling pathways in insects. The TmIKKε gene is characterized by two exons and one intron comprising an open reading frame (ORF) of 2,196 bp that putatively encodes a polypeptide of 731 amino acid residues. Tm IKKε contains a serine/threonine protein kinases catalytic domain. Phylogenetic analysis established the close homology of Tm IKKε to Tribolium castaneum IKKε (Tc IKKε) and its proximity with other IKK-related kinases. The expression of TmIKKε mRNA was elevated in the gut, integument, and hemocytes of the last-instar larva and the fat body, Malpighian tubules, and testis of 5-day-old adults. TmIKKε expression was significantly induced by Escherichia coli , Staphylococcus aureus , and Candida albicans challenge in whole larvae and tissues, such as hemocytes, gut, and fat body. The knockdown of the TmIKKε messenger RNA (mRNA) expression significantly reduced the survival of the larvae against microbial challenges. Further, we investigated the induction patterns of 14 T. molitor antimicrobial peptides (AMPs) genes in TmIKKε gene-silencing model after microbial challenges. While in hemocytes, the transcriptional regulation of most AMPs was negatively regulated in the gut and fat body tissue of T. molitor , AMPs, such as TmTenecin 1 , TmTenecin 4 , TmDefensin , TmColeoptericin A , TmColeoptericin B , TmAttacin 1a , and TmAttacin 2 , were positively regulated in TmIKKε -silenced individuals after microbial challenge. Collectively, the results implicate TmIKKε as an important factor in antimicrobial innate immune responses in T. molitor. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) are considered to be candidate effectors for eliciting humoral immune responses against infectious pathogens in the host. Cecropins are α‐helical peptides of 30–40 amino acids, which are known to permeabilize bacterial membranes, and play authoritative roles in the innate immune system of insects. In the present study, we identified the full‐length open reading frame (ORF) encoding the Tenebrio molitor cecropin‐2 (TmCec2) gene using the Tribolium castaneum cecropin‐2 (TcCec2) gene to query a T. molitor Rnaseq database. Phylogenetic analysis revealed close identity of TmCec2 with TcCec2. TmCec2 was ubiquitously expressed in the insect during all developmental stages, with the highest expression observed in the adult. Tissue‐specific TmCec2 expression was highest in larval hemocytes and in the adult integument and hemocytes. Microbial challenge experiments revealed that TmCec2 was highly induced in response to gram‐positive and gram‐negative bacteria, and fungi. These data provide credible evidence for a putative role of TmCec2 in insect innate immunity against a plethora of pathogens. [ABSTRACT FROM AUTHOR]

Defensins are a major family of antimicrobial peptides that serve as the innate immune defense of both vertebrates and invertebrates. Due to their antimicrobial, chemotactic, and regulatory activities, Defensins have been exploited for their therapeutic potential. Insect Defensins are cysteine‐rich and contain an N‐terminal loop, α‐helix, and antiparallel β‐sheet, forming a "cysteine‐stabilized alpha beta (CSαβ)" or "loop–helix‐sheet" structure. In this study, we identified the full‐length open reading frame (ORF) sequences of Defensin (TmDef) and Defensin‐like (TmDef‐like) genes from the mealworm beetle Tenebrio molitor using in silico methods. TmDef and TmDef‐like genes encode the peptides of 72 and 71 amino acid residues, respectively. TmDefensin is comprised of a Defensin domain and the TmDefensin‐like is comprised of a signal peptide of 21 amino acid residues. Phylogenetic analysis revealed close similarities of TmDefensin with the Defensin of Acalolepta luxuriosa of the longhorn beetle family. The expression of TmDef mRNA was found to be greater than that of TmDef‐like mRNA and was mostly expressed in the pupal and adult stages. Tissue distribution showed high expression of TmDef‐like mRNA in larval hemocytes, gut, integument, and fat body, while in adults, the expression was high in gut and hemocytes. Following bacterial and fungal stimulation in vivo, TmDef was upregulated at 24 h post‐infection in whole body, fat body, and hemocytes of the larvae. Even TmDef‐like mRNA was upregulated in the gut and hemocytes at 12 and 9 h post‐infection respectively. These results suggest that TmDef and TmDef‐like genes play important roles in protecting T. molitor from microbial contact. [ABSTRACT FROM AUTHOR]

Antimicrobial peptides (AMPs) are effector candidates that elicit humoral immunity in invertebrates. AMPs facilitate bacterial clearance by either physically disrupting the microbial membranes or the intracellular targets. In the Coleopteran pest, Tenebrio molitor, transcriptional regulation of AMPs has been studied in the context of innate immune signaling cascades and antimicrobial immunity. Here, we report the transcriptional response of three AMP genes, Coleoptericin A, B, and C (TmCole A, B and C) in T. molitor in response to bacterial (Escherichia coli, Staphylococcus aureus), and fungal (Candida albicans) challenges. These genes were expressed essentially in the gut and hemocytes followed by the integument tissue of the T. molitor larva. Further, these genes were highly expressed in the late‐larval, pupal, and early adult stages. Furthermore, while all of these transcripts were highly upregulated in the fat body and Malpighian tubules after bacterial challenge, TmCole B and TmCole C were induced in the gut after E. coli challenge. Fungal stimulation was not required for the upregulation of the transcription of Coleoptericin genes in T. molitor. [ABSTRACT FROM AUTHOR]

The Riptortus-Burkholderia symbiotic system represents a promising experimental model to study the molecular mechanisms involved in insect-bacterium symbiosis due to the availability of genetically manipulated Burkholderia symbiont. Using transposon mutagenesis screening, we found a symbiosis-deficient mutant that was able to colonize the host insect but failed to induce normal development of host's symbiotic organ. The disrupted gene was identified as purL involved in purine biosynthesis. In vitro growth impairment of the purL mutant and its growth dependency on adenine and adenosine confirmed the functional disruption of the purine synthesis gene. The purL mutant also showed defects in biofilm formation, and this defect was not rescued by supplementation of purine derivatives. When inoculated to host insects, the purL mutant was initially able to colonize the symbiotic organ but failed to attain a normal infection density. The low level of infection density of the purL mutant attenuated the development of the host's symbiotic organ at early instar stages and reduced the host's fitness throughout the nymphal stages. Another symbiont mutant-deficient in a purine biosynthesis gene, purM, showed phenotypes similar to those of the purL mutant both in vitro and in vivo, confirming that the purL phenotypes are due to disrupted purine biosynthesis. These results demonstrate that the purine biosynthesis genes of the Burkholderia symbiont are critical for the successful accommodation of symbiont within the host, thereby facilitating the development of the host's symbiotic organ and enhancing the host's fitness values. [ABSTRACT FROM AUTHOR]

The cystine knot protein Spätzle is a Toll receptor ligand that modulates the intracellular signaling cascade involved in the nuclear factor kappa B (NF-κB)-mediated regulation of antimicrobial peptide (AMP)-encoding genes. Spätzle-mediated activation of the Toll pathway is critical for the innate immune responses of insects against Gram-positive bacteria and fungi. In this study, the open reading frame (ORF) sequence of Spätzle-like from T. molitor (TmSpz-like) identified from the RNA sequencing dataset was cloned and sequenced. The 885-bp TmSpz-like ORF encoded a polypeptide of 294 amino acid residues. TmSpz-like comprised a cystine knot domain with six conserved cysteine residues that formed three disulfide bonds. Additionally, TmSpz-like exhibited the highest amino acid sequence similarity with T. castaneum Spätzle (TcSpz). In the phylogenetic tree, TmSpz-like and TcSpz were located within a single cluster. The expression of TmSpz-like was upregulated in the Malpighian tubules and gut tissues of T. molitor. Additionally, the expression of TmSpz-like in the whole body and gut of the larvae was upregulated at 24 h post-E. coli infection. The results of RNA interference experiments revealed that TmSpz-like is critical for the viability of E. coli-infected T. molitor larvae. Eleven AMP-encoding genes were downregulated in the E. coli-infected TmSpz-like knockdown larvae, which suggested that TmSpz-like positively regulated these genes. Additionally, the NF-κB-encoding genes (TmDorX1, TmDorX2, and TmRelish) were downregulated in the E. coli-infected TmSpz-like knockdown larvae. Thus, TmSpz-like plays a critical role in the regulation of AMP production in T. molitor in response to E. coli infection. [ABSTRACT FROM AUTHOR]