Enhancing wheat-flour safety by detecting and controlling red flour beetle Tribolium castaneum Herbst (Coleoptera: Tenebrionidae)

A functional study of the trehalase genes in Tribolium castaneum and their application in the construction of RNAi engineering bacteria

Tribolium castaneum, belonging to the order Coleoptera, family Tenebrionidae, is a global grain storage pest. The enzyme trehalase can catalyze trehalose decomposition and participate in chitin synthesis, which is of great significance in insect physiology and may be a key target for T. castaneum pest prevention and control. This study focused on T. castaneum and explored the function of its trehalase (TcTre) in test insects' growth and development process. We analyzed the roles of TcTre in different growth stages and tissues of T. castaneum by measuring its spatio and temporal expression patterns. The silencing of TcTre by RNAi technology reduced the transcription level of the target gene, affected the enzyme activity of trehalase, disturbed the sugar balance, blocked the pathway of chitin synthesis, and caused abnormal molting and wing development of the tested insects. Key genes about pest control such as TcTre1-1, TcTre1-3, and TcTre2 were screened, which caused the accumulated mortality of 53.33 %, 56.67 %, and 50.00 % respectively. Subsequently, an engineered bacterium, Tre-L4440-HT115 (DE3), was developed to efficiently express dsRNA and mediate insecticidal activity. The dsRNA produced by the bacterial solution, targeting TcTre1-1, TcTre1-3, and TcTre2 fragments for silencing, could cause the death of 44.44 %, 48.89 %, and 46.67 % of the test insects cumulatively. This advancement was aimed at reducing the production costs of dsRNA and laying a scientific foundation for the industrial development of nucleic acid pesticides for T. castaneum.

RNA interference-mediated silencing of GNBP2 reduces the immunity of stored pest Tribolium castaneum against bacteria

Gram-negative bacteria binding proteins (GNBPs) are involved in regulating the immune response of insects. The information on functions and mechanisms of insect GNBPs in innate immunity will contribute to biological control of pests. Tribolium castaneum is a serious, world-wide pest damaging stored food and feed products. However, the study on roles of GNBPs in T. castaneum innate immunity is relatively scarce. In this research, we identified TcGNBP2, a GNBP2 found in the cDNA library of T. castaneum. Spatiotemporal examination indicated that TcGNBP2 exhibited significant transcription in early pupae stages, and mainly distributed in two immune-related tissues, hemolymph and fatbody. After Escherichia coli or Staphylococcus aureus challenge, TcGNBP2 transcription levels increased significantly from 6 to 72 h. The binding ability of TcGNBP2 to lipopolysaccharide, peptidoglycan, and β-1,3-glucan was predicted by molecular docking analysis and confirmed by ELISA. The subsequent investigation revealed that TcGNBP2 exhibited binding affinity towards five distinct bacterial strains and demonstrated agglutination activity against four of them. Silencing of TcGNBP2 with RNA interference (RNAi) results in the inhibition of antimicrobial peptide gene expression and the prophenoloxidase cascade in beetles upon bacterial challenge, thereby attenuating the immune response of T. castaneum. The survival tests revealed that the knockdown of TcGNBP2 significantly compromised T. castaneum's resistance to bacterial infection. Our findings provide valuable insights into the regulatory mechanism of TcGNBP2 in the innate immunity of T. castaneum and offer a promising molecular target for RNAi-based management of insect pest.

Detection Limits of Insect Fragments in Spiked Whole Wheat Flour Using Multiplex Polymerase Chain Reaction (PCR)

The need for a sensitive molecular method to detect specific species of insect contaminants in food products remains a significant challenge in the food industry. This study evaluated the detection limit of a multiplex end-point PCR assay for detecting insects in food. The assay amplifies two fragments of the cytochrome oxidase subunit I gene (COI-Fa and COI-Fb) and one fragment of the protein-coding wingless (wg) gene found in insects. Five insect species, comprising three vectors of foodborne pathogens (the housefly, Musca domestica, the American cockroach, Periplaneta americana, and the pharaoh ant, Monomorium pharaonis) and two storage insect pests (the red flour beetle, Tribolium castaneum and the Indian meal moth, Plodia interpunctella), were spiked separately and in combination at levels of 1, 0.1, 0.01, and 0.001% in whole wheat flour. At spike levels greater than 0.01%, amplicon bands of expected sizes were seen in 100% of samples containing fragments from distinct insect species. At least 25% of spiked samples at the lowest spike level had amplicon bands, except for samples spiked with M. domestica. Results showed an 18.9% probability (with 11.3% and 30% lower and upper confidence limits, respectively) of detecting insect fragments at the lowest spike level (0.001%, corresponding to 3-22 fragments), which is far below the FDA's regulatory level of less than 75 fragments per 50 g of wheat flour. The intensity of amplicon bands in the gel images was higher at higher spike levels. However, this method is not quantitative enough to extrapolate the intensity of the amplicon bands to the number of insect fragments present in a sample. This multiplex assay was also evaluated in a variety of market food samples derived from plants and animals, showing its potential use in various food types. Overall, the sensitivity and specificity of this molecular approach suggest that it could be used in the future as a screening tool for detecting insect contaminants in food.

Insecticidal and Repellent Activity of Essential Oils from Seven Different Plant Species against Tribolium castaneum (Coleoptera: Tenebrionidae)

Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) is the most destructive pest of stored grain commodities. To control the attack of this insect pest, it is important to develop non-hazardous alternatives to replace fumigants. This study examined the fumigant toxicity and repellent activity of seven essential oils (Chinopodium ambrosiodes, Pinus roxburghii, Zanthoxylum armatum, Lepidium sativum, Azadirachta indica, Baccharis teindalensis, and Origanum majorana) against adult T. castaneum under controlled laboratory conditions. The fumigant toxicity and repellent activities of essential oils were tested using five different doses (62.5, 125, 250, 500, and 1000 µg) in vapour-phase fumigation and four-arm olfactometer bioassays, respectively. In vapor-phase fumigation bioassays, mortality data were recorded after 24, 48, and 72 h. The results showed that C. ambrosiodes and P. roxburghii essential oils are potential fumigants against adult T. castaneum. In repellency bioassays, a one-week-old adult population of T. castaneum was used to test the repellency potential of the essential oils. The results indicated that C. ambrosiodes and P. roxburghii had significant repellency potential against T. castaneum. Overall, we conclude that these essential oils have strong repellent and fumigant properties and can be used as potential repellent compounds to deter the insects.

Dielectric heating for controlling field and storage insect pests in host plants and food products with varying moisture content

At the intersection of insect control and sustainability goals, dielectric heating emerges as a promising solution. In agriculture, where insect pests can reduce agricultural yields and the nutritional quality of crops under field and storage conditions. Chemical pesticides are often used to manage pests but owing to their deleterious consequences on humans and the environment, chemical-free treatments have become the preferred option. Among the existing options, applying radio frequency (RF) and microwave energy for the purpose of dielectric heating has proven to be a successful alternative to chemical pesticides for controlling some major insect pests. This review offers an overview of dielectric heating for pest control in both storage settings and field environments, which addresses pests that impact materials with varying moisture contents (MC). The review highlights the limitation of this technology in controlling insect pests within bulk materials, leading to non-uniform heating. Additionally, it discusses the application of this technology in managing pests affecting materials with high MC, which can result in the degradation of the host material's quality. The review suggests the combination of different techniques proven effective in enhancing heating uniformity, as well as leveraging the non-thermal effects of this technology to maintain the quality of the host material. This is the first review providing an overview of the challenges associated with employing this technology against high moisture content (MC) materials, making it more advantageous for controlling storage pests. Overall, the review indicates that research should particularly emphasize the utilization of this sustainable technology against insect pests that inflict damage on high (MC) substances.

Comprehensive metabolomic variations of hawthorn before and after insect infestation based on the combination analysis of 1H NMR and UPLC-MS

Hawthorn, the sliced and dried ripe fruits of Crataegus pinnatifida Bge. Var. Major N. E. Br. (Rosaceae), is an edible and medicinal substance with a variety of health-promoting benefits. Hawthorn needs to be stored in warehouses after harvesting to meet people's perennial demand. However, it is easily infested by insects of Plodia interpunctella and Tribolium castaneum during storage, which inevitably leads to poor quality and causes adverse effects on people's health. So far, there has been no report on insect-infested hawthorn. In this study, we analyzed the changes of metabolites in hawthorn before and after insect infestation and screened out potential biomarkers to effectively and quickly detect the occurrence of insect infestation. A combination analysis of 1H nuclear magnetic resonance (NMR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) was used to identify the primary and secondary metabolites. By the comparison of hawthorn and insect-infested hawthorn samples, it was found that the differences were mainly manifested in the content of metabolites. The metabolites of 32 and 1463 were identified by 1H NMR and UPLC-MS analysis, respectively. According to the parameters of VIP >1 and P < 0.05, 10 differential metabolites were screened from 1H NMR analysis. Based on the parameters of VIP >1.0, P < 0.05, and (FC) > 1 or < 1, 47 differential metabolites were screened from UPLC-MS analysis. Therefore, a total of 57 differential metabolites were considered as differential biomarkers. The heat map analysis showed that the content of some differential biomarkers with significant pharmacological activities decreased after insect infestation. Through receiver operating characteristic (ROC) curve assessment, 52 differential biomarkers (6 of 1H NMR analysis and 46 of UPLC-MS analysis) were screened to distinguish whether insect infestation occurred in hawthorn. This is the first report on the changes of metabolites between hawthorn and insect-infested hawthorn and on the screening of differential biomarkers for monitoring insects. These results contributed to evaluate quality of hawthorn and ensure food safety for consumers. It also laid a foundation for further research on the infestation mechanism and safe storage monitoring in hawthorn.

Effect of Sitophilus zeamais (Coleoptera: Curculionidae) Infestation on the Protein Physicochemical and Structural Properties of Wheat Grain

Boring pests such as Sitophilus zeamais (S. zeamais) are major threats in grain storage. However, how these pests affect the proteins of stored grains remains largely unknown. Here we aimed to investigate the effect of S. zeamais infestation on wheat protein during postharvest storage. In this study, wheat grain infested by S. zeamais was sampled at egg (4 d), larval (20 d), pupal (35 d), and adult stages (45 d), respectively. The protein's physicochemical and structural properties and the edible quality of whole wheat noodle were analyzed. The results showed that S. zeamais infestation significantly decreased the quality of wheat protein by altering its constitution and structure properties. Especially, compared with the control, the content of wet and dry gluten, gluten index, sodium dodecyl sulfate sedimentation volume, sulfhydryl groups, and disulfide bonds in insect-infested wheat decreased by 19.40, 5.42, 18.40, 8.12, 29.13, and 14.30%, respectively, during the storage period of one life cycle of S. zeamais. Additionally, the proportions of wheat protein fractions (albumin [1.16-fold], globulin [0.96-fold], gliadin [1.16-fold], and glutenin [0.95-fold]) and secondary structures (α-helix [0.91-fold], β-fold [0.96-fold], β-turn [1.06-fold], and random coil [1.05-fold]) of protein changed significantly, and the gluten network structure was broken in S. zeamais-infested wheat. Furthermore, the color of whole wheat noodle became darker, cooking loss rate increased, and textural properties (hardness, adhesiveness, springiness, cohesiveness, chewiness, and resilience) decreased as well. The results in the present study provided new insights for analyzing the quality deterioration mechanism and further quality improvement of boring pests-infested wheat grain.

Cytotoxicity and Genotoxicity Evaluation of Some Stored Grain Insects and Their Infested Flour Using the BHK-21 Cell Line in an In Vitro Experimental Model

Globally, stored grain is vulnerable to pest infestation, resulting in significant economic losses for some crops. Wheat is one of the most important crops in the world. Many sucking, piercing insects infect wheat in the form of grains or flour and may produce toxic residues that are harmful to human health. The current study aimed to estimate the safe use of four stored grain insects by evaluating the potential genotoxic effects and cytotoxicity of crushed insects (T. granarium, S. oryzae, R. dominica, and T. castaneum) and their flour residues. MTT and comet assays were conducted to assess the effects of six concentrations of insect flour residues (0, 6.5, 12.5, 25, 50, and 100%) on the baby hamster kidney cell line (BHK-21). The lowest BHK-21 cell viability was noted against T. granarium (LC50% 36.42 μg/ml) followed by T. castaneum flour (LC50% 46.73 μg/ml) compared to the control (LC50% 808.2 μg/ml). Significantly high DNA comet (%) was observed in the treatments of T. castaneum flour (18.8%), S. oryzae wheat (15.6%), T. granarium (15.4%), T. castaneum (13.6%), and T. granarium wheat (13.1%). FTIR spectra of stored grain insects and their flour residues identified various functional metabolite groups, including alkynes and phenols, which could enhance cell apoptosis and genotoxicity. T. granarium, T. castaneum, and their flour residues had the highest cytotoxic and genotoxic effects on the BHK-21 cell line. The current study concludes that insect residues in flour may have cytotoxic and genotoxic effects on living cells, potentially affecting public health, particularly after consuming T. granarium and T. castaneum-infested flour. Therefore, good storage of stored grains and their products is recommended.