Understanding the ability of internal- and external-infesting stored product insects to vector microbes is important for estimating the relative risk that insects pose to postharvest commodities as they move between habitat patches and in the landscape. Thus, the aim of the current study was to evaluate and compare the microbial growth in novel food patches at different dispersal periods by different populations of Sitophilus oryzae (e.g., internal-infesting) and Lasioderma serricorne (e.g., external-infesting). Adults of both species collected from laboratory colonies or field-captured populations were either placed immediately in a novel food patch, or given a dispersal period of 24 or 72 h in a sterilized environment before entering a surrogate food patch. Vectored microbes in new food patches were imaged after 3 or 5 days of foraging, and microbial growth was processed using ImageJ while fungal species were identified through sequencing the ITS4/5 ribosomal subunit. We found that increasing dispersal time resulted in multiple-fold reductions in microbial growth surrogate food patches by L. serricorne but not S. oryzae. This was likely attributable to higher mobility by S. oryzae than L. serricorne. A total of 20 morphospecies were identified from 13 genera among the 59 sequences, with a total of 23% and 16% classified as Aspergillus and Penicillium spp. Our data suggest that there is a persistent risk of microbial contamination by both species, which has important food safety implications at food facilities.

The Sitophilus zeamais (maize weevil) and Sitophilus oryzae (rice weevil) are two insect pests that have caused huge economic losses to stored grains worldwide. It is urgent to develop an environmentally friendly strategy for the control of these destructive pests. Here, the olfactory-mediated selection preference of the two weevil species to three stored grains was analyzed, which should help establish a pull-push system in managing them. Bioassays showed that maize weevil adults prefer to select maize, followed by paddy and wheat, while rice weevil adults mainly migrate towards wheat. Volatile analyses revealed that 2-ethylhexanol, piperitone, and (+)-Δ-cadiene are the major components in volatiles from both maize and wheat, but the abundance of these chemicals is much lower in maize than that in wheat. The volatile limonene was only detected in paddy. Y-tube bioassays suggest that 2-ethylhexanol, piperitone, and (+)-Δ-cadiene were all attractive to both weevils, whereas limonene was attractive only to rice weevils. Overall, maize weevil appeared more sensitive to the tested volatiles based on having much lower effective concentrations of these volatiles needed to attract them. The differences in volatile profiles among the grains and the sensitivity of the two species towards these volatiles may explain the behavioral differences between maize and rice weevils in selecting host grains. The differences in sensitivity of maize and rice weevils towards host volatile components with abundance differences are likely determinants driving the two insect species to migrate towards different host grains.

Interactions between animals and microbes are ubiquitous in nature and strongly impact animal physiology. These interactions are shaped by the host immune system, which responds to infections and contributes to tailor the associations with beneficial microorganisms. In many insects, beneficial symbiotic associations not only include gut commensals, but also intracellular bacteria, or endosymbionts. Endosymbionts are housed within specialized host cells, the bacteriocytes, and are transmitted vertically across host generations. Host-endosymbiont co-evolution shapes the endosymbiont genome and host immune system, which not only fights against microbial intruders, but also ensures the preservation of endosymbionts and the control of their load and location. The cereal weevil Sitophilus spp. is a remarkable model in which to study the evolutionary adaptation of the immune system to endosymbiosis owing to its binary association with a unique, relatively recently acquired nutritional endosymbiont, Sodalis pierantonius. This Gram-negative bacterium has not experienced the genome size shrinkage observed in long-term endosymbioses and has retained immunogenicity. We focus here on the sixteen antimicrobial peptides (AMPs) identified in the Sitophilus oryzae genome and their expression patterns in different tissues, along host development or upon immune challenges, to address their potential functions in the defensive response and endosymbiosis homeostasis along the insect life cycle. This article is part of the theme issue \'Sculpting the microbiome: how host factors determine and respond to microbial colonization\'.

The present study investigates the chitin properties of stored-product insect pests and their association with the fumigant toxicity of garlic essential oil. Chitin isolates of Callosobruchus maculatus, Sitophilus oryzae, and Tribolium castaneum adults were characterized using FT-IR, XRD, EA, SEM-EDS, and NMR techniques. Fumigant toxicity assay was performed under airtight condition in glass vial. The S. oryzae contains highest chitin content (19 %), followed by T. castaneum (10 %) and C. maculatus (8 %). The degree of crystallinity was lower in C. maculatus (67.13 %) than in S. oryzae (77.05 %) and T. castaneum (76.56 %). Morphologically, C. maculatus chitin displayed a flat lamellar surface with pores, while S. oryzae and T. castaneum exhibited densely arranged microfibrils based surfaces. Fumigant toxicity assays revealed varied susceptibility levels, C. maculatus exhibited higher susceptibility (0.27 μL/L air of LC50) compared to S. oryzae and T. castaneum (14.35 and 3.74 μL/L air of LC50, respectively) to garlic essential oil. The higher chitin content, greater crystallinity, and densely arranged structures in S. oryzae might contribute to its tolerance towards fumigant. Additionally, physico-chemical properties and penetration potentiality of the bioactive constituents might be linked to the toxicity in insects. Understanding these relations can enrich knowledge of chitin\'s role in fumigant toxicity mechanism.

Rice grains are often infected by Sitophilus oryzae due to improper storage, resulting in quality and quantity losses. The efficacy of terahertz time-domain spectroscopy (THz-TDS) technology in detecting Sitophilus oryzae at different stages of infestation in stored rice was employed in the current research. Terahertz (THz) spectra for rice grains infested by Sitophilus oryzae at different growth stages were acquired. Then, the convolutional denoising autoencoder (CDAE) was used to reconstruct THz spectra to reduce the noise-to-signal ratio. Finally, a random forest classification (RFC) model was developed to identify the infestation levels. Results showed that the RFC model based on the reconstructed second-order derivative spectrum with an accuracy of 84.78%, a specificity of 86.75%, a sensitivity of 86.36% and an F1-score of 85.87% performed better than the original first-order derivative THz spectrum with an accuracy of 89.13%, a specificity of 91.38%, a sensitivity of 88.18% and an F1-score of 89.16%. In addition, the convolutional layers inside the CDAE were visualized using feature maps to explain the improvement in results, illustrating that the CDAE can eliminate noise in the spectral data. Overall, THz spectra reconstructed with the CDAE provided a novel method for effective THz detection of infected grains.

The main insect pest of stored paddy is Sitophilus oryzae (rice weevil). Huge amounts of rice are produced by peasant farmers each year, but the bulk of it is wasted due to insufficient storage facilities and insect pest attacks brought on by careless handling. In this study, the insecticidal effects of biochar on S. oryzae were assessed in femurs from Sus scrofa (pig), Gallus gallus (chicken), and Bos taurus (cattle). Adult mortality, adult emergence, weight loss, seed damage, and weevil perforation index are among the indicators evaluated. To apply the biochar, different dosages were used: 0.2, 0.4, 0.6, 0.8, and 1.0 g/20 g of paddy rice. In this work, the population of adult S. oryzae on paddy rice was dramatically reduced by all animal bones biochar tested for insecticidal activity (p < 0.05). The animal bone biochar became more effective with increasing dosage. After 24 h of treatment, pig biochar induced a 36.67 % mortality rate of adult S. oryzae, followed by cow biochar\'s 20 % mortality rate of rice weevils. The fatal dose of cattle, pig, and chicken biochar at which 50 % (LD50) of the population of adult S. oryzae responded after 24 h of treatment were 0.83g, 0.43g, and 0.90g, respectively. It should be encouraged to utilize biochar made from animal bones to combat the S. oryzae in stored paddy. They could be utilized as a green control measure to lessen the risk brought on by the usage of synthetic chemical insecticides in the environment.

The excessive use of synthetic pesticides has detrimental impacts on humans, non-target organisms, and the environment. Insect pest management strategies are shifting toward biopesticides, which can provide a feasible and environmentally friendly green solution to the pest problem. The key objective of the present research work was the preparation of Mentha piperita-based nanobiopesticides with enhanced stability, solubility, and pesticidal potential. Nanobiopesticides based on the Mentha piperita extract were prepared using the antisolvent precipitation method. The central composite design of response surface methodology (RSM) was utilized to optimize different process parameters, e.g., the amounts of the stabilizer and plant extract. The nanosuspension of Mentha piperita prepared with the stabilizer SLS showed a particle size of 259 nm and a polydispersity index of 0.61. The formulated biopesticides in the form of nanosuspensions showed good antibacterial activities as compared to the Mentha piperita extract against two phytopathogenic bacterial strains, Clavibacter michiganensis and Pseudomonas syringae. The M. piperita nanosuspension had higher antifungal efficacy against A. niger and F. oxysporum than the Mentha piperita extract. The M. piperita extract and its nanosuspensions were tested for pesticidal activity against the stored-grain insects Tribolium castaneum and Sitophilus oryzae. Mentha piperita-based nanobiopesticides demonstrated significantly high (p  <  0.05) average mortality of 84.4% and 77.7% against Tribolium castaneum and Sitophilus oryzae, respectively. Mentha piperita-based nanobiopesticides showed enhanced pesticidal potential and could be used as a good alternative to synthetic chemical pesticides.

Blumea balsamifera (L.) DC. (Asteraceae), also known as sambong, is a perennial herb used in China for medicinal purposes. The essential oil (EO) of B. balsamifera was extracted by hydrodistillation. Thirty chemical components of the EO were analyzed by gas chromatography-mass spectrometry (GC-MS) and GC, accounting for 88.0% (w/w) of the total oil. The EO of B. balsamifera was mainly composed of monoterpenes and sesquiterpenes, in which borneol (23.3%), β-caryophyllene (20.9%) and camphor (11.8%) were the major components. The insecticidal activities of the EO and its three main compounds against Tribolium castaneum, Lasioderma serricorne and Sitophilus oryzae were evaluated. The results of bioassays displayed that the EO of B. balsamifera did not have fumigant toxicity to the three target insects, but exhibited significant contact activity against L. serricorne (LD50 = 12.4 μg/adult) and S. oryzae (LD50 = 44.4 μg/adult). Meanwhile, the EO showed a notable repellent effect on T. castaneum at all testing concentrations and a general repellent effect on S. oryzae at high concentrations (78.63 nL/cm2). β-Caryophyllene showed the best performance in the contact toxicity bioassays against the three insects. The results indicated that B. balsamifera has the potential to be used as a source of botanical insecticides for the control of stored-product insects.

Naturally derived essential oils (EOs) from Ocimum basilicum (OB) and Ocimum gratissimum (OG) were incorporated in polylactic acid (PLA) matrix with concentration of 2.5 % and 5 % respectively by solvent casting method, with an aim to develop insecticidal polymer pouches (insect proof polymer pouches). The major components following GC-MS analysis revealed the presence of EOs as estragole (69.998 %) in OB and thymol (29.843 %) in OG. The developed films with EOs showed remarkable insecticidal activity with 100 % and 80 % mortality rate for OB and OG respectively at 2.5 % concentration against rice weevil (Sitophilus oryzae). While, both OB and OG EOs observed 100 % mortality against pulse beetle (Callosobruchus chinensis) after 96 h exposure in presence of grain conditions and the insecticidal efficacy was equivalent to the commercial hermetic bags (CSB). The physical property of film showed increase in the film thickness in EO-PLA films whereas the mechanical properties of EO-PLA films matrix have increased the polymer flexibility with decreasing tensile strength (TS) and Youngs modulus (EM) as TS OB 5 %, OG 5 % - 15.64 MPa, 17.66 MPa respectively. While, water vapour transmission rate (WVTR) was reduced to 0.015 g/m2.hr, optical characteristics showed slight significant change in colour and FTIR spectra exhibited a change in -OH stretching compared to blank PLA matrix. The surface morphology of the blank and EO embedded PLA films visualized by SEM depicted a complete homogenization of essential oils in the PLA matrix.

Clove (Syzygium aromaticum) being a most valuable spice, produce stems and leaves as by-products during processing. This study aimed to valorize these by-products as potential grain protectants against rice weevils since it is a novel approach to reducing the post-harvest loss of rice and minimizing synthetic insecticide usage. The composition of clove stem and leaf essential oils was analyzed using gas chromatography-mass spectrometry. Accordingly, the contact repellent activity and fumigation mortality of essential oils were tested while computing the mortality percentage and LD50 values. The yield of stem essential oil (5.52%) was significantly higher than leaf essential oil (3.92%). Further, stem essential oil with a 100 µL dose showed the highest repellency (100.00 ± 0.00%) and mortality (96.67 ± 3.33%) while 50 and 75 µL doses caused similar mortality (83.30 ± 3.33%) after 5 days. The lowest LD50 (28.06 µL/L) was observed on day 5, indicating the higher toxicity of stem essential oil. Eugenol (73.73 and 82.56%), β-caryophyllene (24.84 and 16.67%), α.-humulene (0.82 and 0.33%), and 1S, CIS-calamenene (0.14 and 0.03%) were detected as the major components responsible for the insecticidal activity of stem and leaf essential oils. Hence, the valorization of clove by-products was successful as potential grain protectants, and clove stem essential oil could be the most effective alternative for rice weevil management.